2025.04.04
Masahito Mochizuki (Prof.) gave an invited talk in the joint workshop of ISSP Supercomputer Center and CCMS (Institute of Solid State Physics, The University of Tokyo, 2025.04.03-04).
Title: Spin-charge excitation dynamics of topological magnetism in Kondo-lattice magnets (in Japanese)
Speakers: Masahito Mochizuki


2025.03.18-21
The following oral presentations were given by our group members in The Physical Society of Japan (JPS) 2025 Spring meeting (Online via Zoom)

Numb.: 18pC1-8
Title: Theory of the microscopic mechanism of photoinduced magnetic phase transitions in the cubic Kondo-lattice model (in Japanese)
Speakers: Hamano Ryo, Masahito Mochizuki

Numb.: 19aC1-1
Title: Theoretical study on the current-induced magnetization switching in antiferromagnetic NiO (in Japanese)
Speakers: Tatsuya Iguchi, Masahito Mochizuki

Numb.: 19aL1-7
Title: Detailed analysis of mathematical model of amoeba-inspired combinatorial optimization machine (in Japanese)
Speakers: Yusuke Miyajima, Masahito Mochizuki

Numb.: 20aC1-1
Title: Current driven antiskyrmion motion on the track
Speakers: Yao Guang, Xichao Zhang, Yizhou Liu, Licong Peng, Yasin sami Fehmi, Kosuke Karube, Naoto Nagaosa, Yasujiro Taguchi, Masahito Mochizuki, Yoshinori Tokura, Xiuzhen Yu

Numb.: 21aE1-5
Title: Photocurrent and high-harmonic generation in B20-type chiral semimetals (in Japanese)
Speakers: Yuya Ominato, Masahito Mochizuki

2025.03.17
The following oral presentation will be given in the 72st Spring Meeting of the Japan Society of Applied Physics (JSAP)（Tokyo University of Science, Noda campus + Online）.

Numb.: 17a-K306-1
Title: Detailed analysis of mathematical model of amoeba-inspired combinatorial optimization machine (in Japanese)
Speakers: Yusuke Miyajima, Masahito Mochizuki

2025.03.16-21
The following oral presentations were given by our group members in APS March Meeting 2025 (Anaheim, CA, USA).
Numb.: MAR-C52-7 (4:36 PM-4:48 PM, March 17 (Mon.), 2025, Anaheim Convention Center, 259B)
Title: Theory of transformations among skyrmion, antiskyrmion and non-topological bubble with in-plane magnetic field in noncentrosymmetric dipolar magnets
Speakers: Tatsuki Muto, Masahito Mochizuki

Numb.: MAR-F48-1 (8:00 AM-8:12 AM, March 18 (Tue.), 2025, Anaheim Convention Center, 262A)
Title: Predicted multiple Walker breakdowns for current-driven domain-wall motion in antiferromagnets
Speakers: Mu-Kun Li, Masahito Mochizuki, Rubén M Otxoa

Numb.: MAR-N40-4 (4:00 PM-4:12 PM, March 19 (Wed.), 2025, Anaheim Convention Center, 264C)
Title: Resummed Topological Magnons in Honeycomb Ferromagnets
Speakers: Rintaro Eto, Masahito Mochizuki, Alexander Mook

Numb.: MAR-T50-7 (4:36 PM-4:48 PM, March 20 (Thu.), 2025, Anaheim Convention Center, 260B)
Title: Nonlinear Spin-Wave Theory in Altermagnets: Spontaneous Magnon Decays from Nonrelativistic Band Splitting
Speakers: Alexander Mook, Alexander L. Chernyshev, Rintaro Eto, Matthias Gohlke, Masahito Mochizuki

2025.03.04
Yusuke Miyajima (D3/Research associate) gave an oral talk and a poster presentation at the international conference, The 6th International Symposium on Neuromorphic AI Hardware ([web]) held in Hotal Crown Palais, Kitakyushu-shi, Japan (2025.03.03-04).

Numb.: P2-13
Title: Detailed analysis of mathematical model of amoeba-inspired combinatorial optimization machine
Speakers: Yusuke Miyajima, Masahito Mochizuki
2025.02.28
Grant-in-Aid for for Young Scientists (Rep: Xichao ZHANG) [FY2025-2027] has been accepted.

Research Subject: Research for device functions of topological magnetic textures at nanofunctional interfaces

2025.02.28
Grant-in-Aid for Scientific Research (A) (Rep: Masahito MOCHIZUKI) [FY2025-2028] has been accepted.

Research Subject: Explorations of material functions and physical phenomena of magnetic skyrmions and creations of skyrmionics"

2025.02.03
The graduation thesis presentations of the Department of Applied Physics and the Department of Physics were held. Three students from our group, Manaki Arihara, Hironosuke Kobayashi, and Aoba Yasuda, gave presentations.

【Bachelor Thesis Titles】
Manaki Arihara: Theoretical study on the photoinduced phase transitions in the Kagome Kondo-lattice model with spin-orbit interactions

Hironosuke Kobayashi: Theoretical study on the thermally assisted photoinduced magnetic topological phase transitions in the J1-J3 classical Heisenberg model on a triangular lattice

Aoba Yasuda: Theoretical study on the magnetic-field-induced ferroelectric polarization flop in multiferroic perovskite manganites

2025.02.03
Xichao ZHANG (張渓超) received the 2024 Waseda University Research Award (High-Impact Publication) [web]. The award ceremony and celebration reception were held at the Okuma Hall [Album].
[Movie]。

2024.12.19 The following invited paper about the machine-learning techniques for detection of the Berezinskii-Kosterlitz-Thouless transitions in spin models was published in Journal of the Physical Society of Japan as a Special Topics for the machine learning physics. Masahito Mochizuki, Yusuke Miyajima Journal of the Physical Society of Japan 94, 031003/1-13 (2024). Title: Machine-Learning Detection of the Berezinskii-Kosterlitz-Thouless Transitions

2024.12.18
Xichao Zhang has been selected as a recipient of the 2024 Waseda University Research Award (High-Impact Publication)[web]. The award ceremony will be held on 2025.02.03 (Mon) at the Okuma Kaikan, Waseda Campus.

2024.12.18
Dr. Yuta YAMANE (Frontier Research Institute for Interdisciplinary Sciences (FRIS), Tohoku University) stayed in our group for a week and gave a seminar talk[Album].
Title: Theoretical study on emergent electromagnetic indantance

2024.12.13 The following review paper about the skyrmion Hall effects was published in Applied Physics Review. Sheng Yang, Yuelei Zhao, Xichao Zhang, Xingxiang Jun, Xiaoguang Li, Masahito Mochizuki, Xiaohong Xu, Johan Åkerman, Yan Zhou Applied Physics Review 11, 041335/1-28 (2024). Title: The Fundamentals and Applications of the Skyrmion Hall Effect

2024.11.25
Rintaro Eto (D2) gave a poster presentation in ISSP Theory mini-Workshop ``Correlated Quantum Materials + beyond" CQM+b2024 (Institute for Solid State Physics, University of Tokyo, Kashiwa, Japan, 11/18-29)
Title: Resummed Topological Magnons in Honeycomb Ferromagnets


2024.11.13
Dr. Rintaro Eto (D2) has returned from Germany. He stayed in Alexander Mook's group at Johannes Gutenberg University Mainz for 6 months supported by the JSPS Young Researchers Overseas Challenge Program to conduct collaborative theoretical research on many-body correlation effects on magnetic excitations in ferromagnets and alternmagnets.

2024.10.21 The following paper was published in Journal of Physics: Condensed Matter as a topical review (invited). IIn this review article, fundamental and systematic theoretical descriptions based on Thiele equation for current-induced motion of magnetic skyrmions are discussed by particularly focusing on dependence of the direction and velocity of motion on several factors and conditions, e.g., the driving mechanism, the type of skyrmion, the system geometry, the direction of applied current, and the type of magnet. Yuto Ohki, Masahito Mochizuki Journal of Physics: Condensed Matter 37, 023003/1-30 (2024). Title: Fundamental theory of current-induced motion of magnetic skyrmions

2024.09.30 The following paper was published in Nonlinear Theory and Its Applications, IEICE. In this work, an improved mathematical model of the solution-seeking process of a single-celled amoeba solving a traveling salesman problem through shape-shifting dynamics has been published in Nonlinear Theory and Its Applications, IEICE (NOLTA). The proposed modified model reveals that the volume conservation law, which has been aively assumed and an obstacle to physical implementation, can be modified and the quality of the solution is significantly improved. Yusuke Miyajima, Masahito Mochizuki Nonlinear Theory and Its Applications, IEICE 153, 824-837 (2024). Title: Proposed modified computational model for the amoeba-inspired combinatorial optimization machine

2024.09.25
Masahito Mochizuki (Prof.) gave an oral talk in the area workshop for Grant-in-Aid for Transformative Research Areas (A)``Foundation of Machine Learning Physics" (Koshiba hall, Hongo campus, Univ. of Tokyo, Tokyo, 9/25-27)
Title: Development of versatile machine learning methods for detection of the topological phase transitions in spin models

2024.09.24 The following paper was published in Physical Review Letters. In this work, magnetic resonance dynamics of a polar magnet VOSe2O5, which hosts rich nontrivial magnetic phases including a Néel-type skyrmion crystal phase, was studied in collaboration with an experimental group. It is demonstrated that this material provides a unique platform for a comprehensive understanding of resonant spin dynamics in polar magnets. Tomonao Araki, Rina Takagi, Takashi Kurumaji, Yoshinori Tokura, Masahito Mochizuki, and Shinichiro Seki Physical Review Letters 133, 136702/1-6 (2024). Title: Exotic Spin Excitations in a Polar Magnet VOSe2O5

2024.09.16-19
The following oral presentations were given by our group members in The Physical Society of Japan (JPS) 2024 Annual meeting (Sapporo campus, Hokkaido University, Sapporo, Japan)

Numb.: 16aS101-7
Title: Theory of the photo-induced magnetic phase transitions in the cubic Kondo-lattice model (in Japanese)
Speakers: Hamano Ryo, Masahito Mochizuki

Numb.: 18aS101-7
Title: Mutual transformations among skyrmions, antiskyrmions, and topological bubbles in a system with competing magnetic dipole interactions and Dzyaloshinskii-Moriya interactions (in Japanese)
Speakers: Tatsuki Muto, Masahito Mochizuki

2024.09.13 The following invited paper about the theoretical modeling and the magnetoelectric phenomena of the multiferroic perovskite manganites was published in Journal of the Physical Society of Japan as a Special Topics for the 70th anniversary of publication of the Tanabe-Sugano diagram paper. Masahito Mochizuki Journal of the Physical Society of Japan 93, 121004/1-16 (2024). Title: Modeling and Physics of Multiferroic Perovskite Manganites

2024.09.10-12
The following presentations were given by our group members in International conference on 70 years of the Tanabe-Sugano diagrams (TSD70) held in September 10-12, 2024 at Waseda University, Nishi-Waseda Campus, Tokyo, Japan.

Invited Talk
Date&Time: 2024.09.11 (Wed) 15:00-15:20
Title: Modeling and physics of the multiferroic perovskite manganites
Speaker: Masahito Mochizuki

Poster Presentation
Numb.: P11
Title: Chiral Magnetic Skyrmions Interacting with Chiral Flower-Like Nanostructures
Presenter: Xichao Zhang（張渓超）

Numb.: PS12
Title: Dynamical Majorana Ising spin response in a topological superconductor-magnet hybrid by microwave irradiation
Presenter: Yuya Ominato（大湊友也）

Numb.: PS13
Title: Predicted Multiple Walker Breakdowns for Current-Driven Domain-Wall Motion in Antiferromagnets
Presenter: Mu-Kun Lee

Numb.: PS14
Title: Theory of topological spin-polarization textures induced by dipole interactions in the spin-lattice coupled systems
Presenter: Tatsuki Muto（武藤竜樹）

Numb.: PS15
Title: High-frequency magnetic response in antiferromagnetic NiO
Presenter: Tatsuya Iguchi（井口達哉）

Numb.: PS16
Title: Theoretical Study of the Photo-Induced Magnetic Transition in the Kondo-Lattice Model
Presenter: Ryo Hamano（濱野遼宇）

2024.09.09
Rintaro Eto (PhD candidate) stayed in Prof. Johannes Knolle's group in Technical University of Munich and gave a seminar talk.

Title: Resummed Topological Magnons

2024.09.04 The following paper was published in Nature Communications. In this work, we investigated the current-driven dynamics of antiskirmions confined in magnetic stripe domains in collaboration with an experimental group and demonstrated the racetrack memory function of antiskirmions. Yao Guang, Xichao Zhang, Yizhou Liu, Licong Peng, Fehmi Sami Yasin, Kosuke Karube, Daisuke Nakamura, Naoto Nagaosa, Yasujiro Taguchi, Masahito Mochizuki, Yoshinori Tokura, and Xiuzhen Yu Nature Communications 15, 7701/1-8 (2024). Title: Confined antiskyrmion motion driven by electric current excitations

Press release (in Japanese)（2024.09.04）

「レーストラックアンチスキルミオンの動作実証に成功－次世代の情報デバイス開拓に期待－」

・Waseda University

・RIKEN

・Univ. of Tokyo

2024.08.08 The following paper was published in Physical Review B. In this work, we investigated the effect of irradiation with circularly polarized light on the Dirac semimetallic state induced by ferrimagnetic order in the triangular Kondo-lattice model using Floquet theory. We discovered two Floquet-Chern insulater phases as photoinduced nonequilibrium steady states and revealed that these phases originate from higher-order terms in the Brillouin-Wigner expansion of the Floquet theory. Rintaro Eto, and Masahito Mochizuki Physical Review B 110, 085117/1-13 (2024). Title: Multiple Floquet Chern insulator phases in the spin-charge coupled triangular-lattice ferrimagnet: Crucial roles of higher-order terms in the high-frequency expansion

2024.08.06
Xichao Zhang (張渓超・Research Assistant Prof.) gave an invited talk at the International Conference on New Frontiers in Advanced Magnetism (NFAM2024) held in August 5-9, 2024 at Hokkaido University, Sapporo campus, Hokkaido, Japan.

Title: Dynamics of topological spin textures

2024.08.04
Prof. Mochizuki gave a seminar lecture in the 69th Condensed Matter Physics Summer School for young researchers [web] held in Hotal Tatsuki, Gamagori, Aichi.

Title: Theory of the current-induced dynamics of magnetic skyrmions (in Japanese)

2024.07.31-08.01
Prof. Mochizuki and Yusuke Miyajima (D3) gave the following oral talks in the 3rd condensed-matter group meeting for Grant-in-Aid for Transformative Research Areas (A)``Foundation of Machine Learning Physics" (Bldg 11, Room 311, Yotsuya campus, Sophia University, 7/31-8/1)

Date&Time: 2024.07.31(Wed) 16:10-16:40
Title: アメーバ模倣型組合せ最適化マシンの改良数理モデルの提案 (in Japanese)
Author: Yusuke Miyajima (宮島悠輔)

Date&Time: 2024.08.01(Thu) 10:40-11:10
Title: スキルミオンスピン波リザバーコンピューティング素子の理論設計 (in Japanese)
Author: Masahito Mochizuki (望月維人)

2024.07.31 The following paper was published in the Letter section of Physical Review B. In this work, we theoretically predicted possible multiple Walker breakdowns of the current-driven magnetic wall in layered antiferromagnets due to Lorentz contraction of the wall width. This achievement is expected to make an important contribution to the rapidly growing research field of antiferromagnetic spintronics. Mu-Kun Lee, Rubén M. Otxoa, and Masahito Mochizuki Physical Review B 110, L020408/1-6 (2024). Title: Predicted Multiple Walker Breakdowns for Current-Driven Domain-Wall Motion in Antiferromagnets

2024年7月24日 The following invited paper was published in Activity Report FY2023 for Supercomputer Center, Institute for Solid State Physics, The University of Tokyo. Masahito Mochizuki and Rintaro Eto Theoretical studies on the spin-charge dynamics in Kondo-lattice models Activity Report FY2023/ Supercomputer Center, Institute for Solid State Physics, The University of Tokyo pp. 23-36 (ISSN 2188-5001). A figure in this paper was selected as a cover figure.→

2024.07.18
Prof. Mochizuki gave an invited talk at the 14th International Conference on Metamaterials, Photonic Crystals and Plasmonics (META2024) held in July 16-19 at Toyama International Conference Center, Toyama, Japan.

Title: Thermally induced dynamics of magnetic skyrmions and their device functions

2024.07.17 The following paper was published in Applied Physics Letters. In this paper, we demonstrate that long and short current pulses applied to square-cell skyrmions on a square-lattice grid pattern can induce I-, L-, Z-type and even more complex polyomino-like structural changes without changing the topological charge number. Jing Xia, Xichao Zhang, Yan Zhou, Xiaoxi Liu, Guoping Zhao, and Masahito Mochizuki Applied Physics Letters 125, 032404/1-7 (2024). Title: Transformation of a cellular skyrmion to polyomino-like structures

2024.07.16 The following paper was published in Physical Review B. In this paper, we theoretically reveal effects of the chiral damping and the Dzyaloshinskii-Moriya interactions on the current-induced dynamics of magnetic domains in chiral ferromagnetic nanowires. Collins Ashu Akosa, Gen Tatara, Aurelien Manchon, and Masahito Mochizuki Physical Review B 110, 024420/1-8 (2024). Title: Decoupling the influences of chiral damping and Dzyaloshinskii-Moriya interaction in chiral magnetic domain walls

2024.07.15 An article (in Japanese) was published in Kotaibutsuri journal. Rintaro Eto and Masahito Mochizuki Kotaibutsuri Vol. 59, Issue 7 (2024.07. Topics) pp. 13(369)-24(380) Title: Theory of the spin-charge excitations of topological magnetism manifested in Kondo-lattice magnets Our figure was selected as a cover art.→

2024.07.08
Rintaro Eto (D2) gave a poster presentation at the 25th International Colloquium on Magnetic Films and Surfaces (ICMFS2024) (ICMFS2024) held in July 7-12, 2024 at Hotel Gio Conference Center, Perugia, Italy.

Title: Spin-wave modes and real-space topology in the quadruple-Q magnetic hedgehog lattices

Congratulations! He received the Best Poster Presentation Award (sponsored by J. Phys. Materials). [honorable certificate]。

2024.07.02 An invited article was published in News & Views in Nature Materials. Masahito Mochizuki Nature Materials 23, 872-873 (2024). Title: Writing a magnetic whirl on multiferroics

2024.05.31 The following paper was published in Physical Review Letters. In this work, we theoretical discovered and clarified collective excitation modes in quadruple-Q magnetic hedgehog lattices in three-dimensional Kondo lattice magnets. Two of the three oscillation modes in the subterahertz regime correspond to translational oscillations of two types of Dirac strings in the unit cell, which are vortex-like magnetization structures connecting magnetic hedgehog and antimagnetic hedgehog, and the modes disappear when the Dirac strings disappear due to hedgehog-antihedgehog pari annihilations under a magnetic field. These important finds will serve as a foundation for fundamental and applied research on the dynamical behaviors of magnetic (anti)hedgehogs that behave as emergent (anti)monopoles in magnetic materials. Rintaro Eto, Masahito Mochizuki Physical Review Letters 132, 226705/1-7 (2024). Title: Theory of collective excitations in the quadruple-Q magnetic hedgehog lattices

Press release（2024.06.13）

"Uncovering the nature of emergent magnetic monopoles"

・Waseda University

・EurekAlert!

・AlphaGalileo

・Phys.org/Physics News




2024.05.30
Prof. Mochizuki gave an oral talk in the kick-off meeting for Grant-in-Aid for Transformative Research Areas (A)``Chimera Quasi-particles"[web] held on Kuramae kaikan, Tokyo Institute of Technology, Tokyo.

Title: マルチフェロイクスやトポロジカル磁性体に現れるキメラ準粒子の理論 (in Japanese)

2024.05.24 The following paper was published in Aggregate. In this work, we demonstrated by micromagnetic simulations that topological magnetic textures called bimerons, which appear in chiral magnets, show proliferations, aggregations, and dynamical crystal-structure transformations when they are driven by electric currents with spin-transfer torques. Xichao Zhang, Yan Zhou, Xiuzhen Yu, Masahito Mochizuki Aggregate (2024), Early View. Title: Bimerons create bimerons: Proliferation and aggregation induced by currents and magnetic fields

2024.05.22 The following paper was published in Physical Review Research. In this work, we theoretically discovered that the skyrmion Hall effect, which appear in current-driven skyrmion motion as a crucial problem against their technical applications, can be suppressed by using synthetic ferrimagnetic systems with magnetization gradient. Lan Bo, Xichao Zhang, Masahito Mochizuki, Xuefeng Zhang Physical Review Research 6, 023199/1-9 (2024). Title: Suppression of the Skyrmion Hall Effect in Synthetic Ferrimagnets with Gradient Magnetization

2024.05.17
Rintaro Eto (D2) left for Germany. He will stay with Alexander Mook's group at Johannes Gutenberg University Mainz for 6 months to collaborate on magnetic excitations in ferromagnets and altermagnets, supported by the JSPS Young Researchers Overseas Challenge Program.

2024.05.06 The following paper was published in Physical Review Letters, which theoretically proposed a magnon-skyrmion hybrid quantum system. We contributed to this work with micromagnetic simulations of the skyrmion excitations. Xue-Feng Pan, Peng-Bo Li, Xin-Lei Hei, Xichao Zhang, Masahito Mochizuki, Franco Nori Physical Review Letters 132, 193601/1-10 (2024). Title: Magnon-Skyrmion Hybrid Quantum Systems: Tailoring Interactions via Magnons

2024.04.28
Prof. Mochizuki gave an invited talk at the 9th International Conference on Superconductivity and Magnetism (ICSM2024) held at Liberty Hotels Lykia in Ölüdeniz, Turkey (27th April - 4th May, 2024).

Title：Thermally Induced Dynamics of Magnetic Skyrmions and Their Device Functions

2024.04.10
Dr. Charles Reichhardt (Los Alamos National Laboratory, USA) gave a seminar talk[Abstract], [Album].
Date: 2024.04.10(Wed.) 10:45
Place: Bldg. 55N, 2F, Meeting Room, Nishi-Waseda campus, Waseda University
Title: Dynamics of Chiral Systems, Vortices, Skyrmions, and Active Matter
Speaker: Dr. Charles Reichhardt（Los Alamos National Laboratory, USA）
2024.04.08
Yusuke Miyajima (D3/Research associate) gave an oral talk and a poster presentation at the international conference on Materials Meet Robots 2024 (MMR2024) held in Kitakyushu-shi, Japan (7th May - 8th May, 2024).

Title: Proposed computational models of Amoeba-inspired combinatorial optimization machines towards the physical implementation

2024.04.01
Tatsuki Muto (D1) has been appointed as a research associate, and four new members have joined our group[Member]. The new members are as follows, Yusuke Kobayashi (M1), Manaki Arihara (B4), Hironosuke Kobayashi (B4), and Aoba Yasuda (B4).

2024.03.31
Prof. Masatoshi Imada（Visiting Research Prof.），Ryui Kaneko（Research Associate Prof.），Aya Kitano（Secretary of Imada group）left our group.

2024.03.26
Two students, Takaaki Iijima and Tatsuki Muto, have completed their master's degree in the Department of Physics and Applied Physics at Waseda University[Album].

2024.03.26
Three students, Yuki Akishige, Tatsuya Iguchi, and Ryo Hamano, graduated from the Department of Physics and the Department of Applied Physics at Waseda University[Album].

2024.3.22
A farewell party was held at a Chinese restaurant (皇家龍鳳) in Rihga Royal Hotel [Album].

2024.03.23
The following oral presentation will be given in the 71st Spring Meeting of the Japan Society of Applied Physics (JSAP)（Tokyo City University, Setagaya campus + Online）.

Numb.: 23p-22B-10
Title: Proposal of a mathematical model of amoeba-inspired combinatorial optimization machines: simplification towards physical implementations
Speakers: Yusuke Miyajima, Masahito Mochizuki

2024.03.18-20
The following oral presentations were given in 2024 Spring Meeting of the Physical Society of Japan (Online),

Numb.: 18pC1-5
Title: Theoretical study of photoinduced magnetic phase transition and photoinduced topological magnetism in the J1-J3 classical Heisenberg model on a triangular lattice
Speakers: Takaaki Iijima, Masahito Mochizuki

Numb.: 18pL2-13
Title: Improved mathematical model of amoeba-inspired combinatorial optimization machines
Speakers: Yusuke Miyajima, Masahito Mochizuki

Numb.: 20aC2-5
Title: Interaction engineering: Anharmonic effects on magnons in the sawtooth chain antiferromagnet Fe₂Se₂O₇
Speakers: Rintaro Eto, Masahito Mochizuki, Alexander Mook

2024.03.15
The following poster presentations were given in the 22nd Japan-Korea-Taiwan Symposium on Strongly Correlated Electron Systems (JKT22).

Numb.: PS-10
Title: Interaction engineering: Anharmonic effects on magnons in the sawtooth chain antiferromagnet Fe₂Se₂O₇
Presenter: Rintaro Eto

Numb.: PS-26
Title: Theory of chiral damping in ferromagnetic and antiferromagnetic textures
Presenter: Collins Akosa

Numb.: PS-36
Title: Theoretical study of the photoinduced magnetic transition in the Kondo lattice model
Presenter: Ryo Hamano

2024.03.07
Keisuke Kitayama (former graduate student) will give an oral talk in American Physical Society (APS) March meeting 2024 held at Minneapolis convention center in Minneapolis, MN, USA.

Numb.: S04.00003
Title: Predicted Novel Type of Photoinduced Topological Phase Transition Accompanied by Collision and Collapse of Dirac-cone Pair in Organic Salt α-(BEDT-TTF)₂I₃
Speakers: Keisuke Kitayama, Masao Ogata, Yasuhiro Tanaka, Masahito Mochizuki

2024.03.04 The following paper was published in Physical Review Research. In this paper, we theoretically discuss the stability against thermal fluctuations and thermally-induced annihilation dynamics of a topological magnetic texture called skyrmionium that emerges in chiral magnets. Anjie Jiang, Yan Zhou, Xichao Zhang, Masahito Mochizuki Physical Review Research 6, 013229/1-16 (2024). Title: Micromagnetic theory of a type of thermal annihilation of magnetic skyrmionium

2024.03.02
Yusuke Miyajima（D2) gave a poster presentation in the 5th International Symposium on Neuromorphic AI Hardware[web] held at Rihga Royal Hotel Kokura in Kitakyushu, Fukuoka in 3/1-2.

Title: Proposal of computational models of Amoeba-inspired combinatorial optimization machines
Presenters: : Yusuke Miyajima, Masahito Mochizuki

2024.2.29
The KAKENHI project "Chimera Particles" (led by Shuichi Murakami, Tokyo Institute of Technology), in which Mochizuki participates as a member of the project team, has been accepted.

2024.02.13 The following paper was published in Journal of Applied Physics. In this work, we focused on topological magnetic structures called skyrmion bags, in which multiple small skyrmions exist inside a large skyrmion. Using micromagnetic simulations, we discovered a phenomenon that microwave excitation induces global rotation of the inner skyrmions and elucidated its physical mechanism. Lan Bo, Rongzhi Zhao, Xichao Zhang, Masahito Mochizuki, Xuefeng Zhang Journal of Applied Physics 135, 063905/1-6 (2024). Title: Global rotation of skyrmion bags under vertical microwave fields

2024.02.03
The graduation thesis presentations of the Department of Applied Physics and the Department of Physics were held. Three students from our group, Yuki Akishige, Tatsuya Iguchi, and Ryo Hamano, gave presentations.

【Bachelor Thesis Titles】
Yuki Akishige ``Theory of Photoinduced Polarization Domain Dynamics in Proton-Transfer Ferroelectrics"
Tatsuya Iguchi ``Theoretical study of magnetic resonance excitations in antiferromagnetic NiO"
Ryo Hamano ``Theoretical study of photoinduced magnetic transitions in Kondo-lattice magnets"

2024.02.04
The master's thesis presentations of the Department of Physics and Applied Physics were held. Two students from our group, Takaaki Iijima and Tatsuki Muto, gave presentations.

【Mater's Thesis Titles】
Takaaki Iijima ``Theoretical study of photoinduced magnetic phase transitions and photoinduced topological magnetism in the J1-J3 classical Heisenberg model on a triangular lattice"
Tatsuki Muto ``Elucidation of stabilization mechanisms and exploration of physical properties of skyrmions in magnetic dipolar systems"

2023.12.18.
Rintaro Eto (Ph.D student) was selected for the JSPS 2024 Young Researcher Overseas Challenge Program [web].

2023.12.18
Lan Bo (visiting student) has left from our group after a one-year stay. We wish him all the best in his future endeavors.

2023.12.6 The following paper was published in Nano Letters. In this work, we discovered that when magnetic skyrmions are confined in an obstacle pattern called chiral flower, they exhibit one of the typical active-matter behaviors called chiral swimmer due to the Brownian motion with broken rightward and leftward symmetry in numerical simulations and uncovered a physical mechanism behind it. The discovery of active matter behavior, which is conventionally exhibited only by materialsof biological origin, in skyrmions is expected to lead to new development of the research for active matters. Xichao Zhang, Jing Xia, Oleg A. Tretiakov, Motohiko Ezawa, Guoping Zhao, Yan Zhou, Xiaoxi Liu, Masahito Mochizuki Nano Letters 23, 11793-11801 (2023). Title: Chiral Skyrmions Interacting with Chiral Flowers

Press release（2024.2.13）

Scientists study the behaviors of chiral skyrmions in chiral flower-like obstacles

・Waseda University

・EurekAlert!

・Phys.org/Physics News


2023.11.28
A farewell party was held for two exchange Ph.D students, Lan Bo and Javier Vélez, at Shara (酒洛), Takadanobaba.
[Photo1], [Photo2]

2023.11.24
Yusuke Miyajima（D2) gave a poster presentation in a conference (第17回物性科学領域横断研究会)[web] held in November 24,25 at Nagoya Institute of Technology[photo].

Title: Machine learning detection of phase transitions in two-dimensional spin models: the second-order transitions and the Berezinskii-Kosterlitz-Thouless transitions
Speaker: Yusuke Miyajima

2023.11.23 The following paper was published in Advanced Materials. In this work, we achieved and demonstrated controlled creation of several kinds of topological magnetic structures in the chiral magnet Fe0.5Co0.5Ge, including meron-antimeron pairs and bimerons, transformation from skyrmions to bimerons, and current-induced splitting and aggregation of bimerons, in a joint experimental and theoretical study. This achievement adds an novel important insight to the study of manipulation of topological magnetism with external fields. Xiuzhen Yu, Naoya Kanazawa, Xichao Zhang, Yoshio Takahashi, Konstantin V. Iakoubovskii, Kiyomi Nakajima, Toshiaki Tanigaki, Masahito Mochizuki, Yoshinori Tokura Advanced Materials 36, 2306441/1-9 (2023). 題名: Spontaneous Vortex-Antivortex Pairs And Their Topological Transitions in A Chiral-Lattice Magnet

2023.11.21
Risako Kikuchi (Nagoya University) gave a seminar talk.
Date: 2023.11.21(Tue.) 13:30
Place: Bldg. 55N, Nishi-Waseda campus, Waseda university
Title: Quantum transport phenomena of spin-1 fermions
Speaker: Risako Kikuchi (Nagoya University, Ph.D student)
2023.11.15
Prof. Shinichiro Seki (University of Tokyo) gave a seminar talk.
Date: 2023.11.15 (Wed.) 15:30
Place: Bldg. 55N, Nishi-Waseda campus, Waseda university
Title: Emergent physical phenomena exhibited by topological magnetism
Speaker: Shinichiro Seki (University of Tokyo)
2023.11.14
Yusuke Miyajima（D2) gave a poster presentation in the international conference on MACHINE LEARNING PHYSICS[web] held in November 13-18 at Yukawa Institute for Theoretical Physics, Kyoto University.

Title: Machine-learning detection of the Berezinskii-Kosterlitz-Thouless transition and the second-order transition in two-dimensional spin models
Presenter: Yusuke Miyajima

2023.11.14
Prof. Naoya Kanazawa (University of Tokyo) gave a seminar talk.
Date: 2023.11.14 (Tue.) 15:30
Place: Bldg. 55N, Nishi-Waseda campus, Waseda university＋Zoom (hybrid)
Title: Topology of Electronic and Spin States in Chiral Crystals: Focusing on Emergent Monopoles in MnGe and Ferromagnetic Surface States in FeSi
Speaker: Naoya Kanazawa (University of Tokyo)
2023.11.14
Yusuke Miyajima（D3）will give a poster presentation in the international conference on MACHINE LEARNING PHYSICS [web]) held at Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, Japan.

Title：Machine-learning detection of the Berezinskii-Kosterlitz-Thouless transition and the second-order transition in two-dimensional spin models
Speaker：Yusuke Miyajima

2023.11.13
Javier Vélez will give the following seminar talk[abstract].
Date&Time：2023/11/13, 14:00-
Place：Bldg. 55N(North Tower), 2nd floor, Department meeting room, Nishi-Waseda campus, Waseda University
Title：Relativistic Dynamics of Antiferromagnetic Domain Walls: Route to Chaos
Speaker：Javier Vélez（Universidad Del Pais Vasco, Spain・PhD student）

2023.11.08 The following paper has been published in Scientific Reports. In this paper, by performing numerical simulations, we demonstrate that reservoir computing based on spin waves propagating in a skyrmion lattice confined in a thin-plate magnet possesses high capability of handwritten digit recognition. We obtain a high recognition rate of more than 88%, higher by about 10% than a baseline taken as the echo state network model. Mu-Kun Lee, Masahito Mochizuki Scientific Reports 13, 19423 (2023). Title：Handwritten digit recognition by spin waves in a Skyrmion reservoir

2023.11.02
A visiting Ph.D student from Universidad del Pais Vasco (Spain), Javier Antonio Velez Simanca, joined our group. He will stay for a month [Member].

2023.10.24 The following paper has been published in Physical Review B. In this paper, the fluid behaviors of flowing skyrmion particles driven by electric current in a pipe channel are investigated by micromagnetic simulations. We discovered sevela interesting aspects peculiar to the skyrmion flow such as laminar flow, transiently disordered dynamics, dynamical formation and transition of lattice structures, their compression toward the channel edge and so on. Xichao Zhang, Jing Xia, Oleg A. Tretiakov, Motohiko Ezawa, Guoping Zhao, Yan Zhou, Xiaoxi Liu, Masahito Mochizuki Phys. Rev. B 108, 144428/1-14 (2023). Title：Laminar and Quasi-Turbulent Dynamics of a Magnetic Skyrmion Pipe Flow

2023.09.28
Collins Akosa Ashu (Research associate) gave an invited talk at the 3rd African Conf of Fundamental and Applied Physics (ACP2023) held at Nelson Mandela University, Geroge Campus, Gerorge, South Africa (September 25-29, 2023).

Title：Introduction to spintronics: (c.f. Overcoming the skyrmion Hall effect)

2023.09.28
Xichao Zhang (張渓超, PD・Research assistant professor) received the MSJ Distinguished Paper Award from Magnetic Society of Japan.

Title: Current-Induced Helicity Switching of Frustrated Skyrmions on a Square-Grid Obstacle Pattern
Authors: X. Zhang, J. Xia, O. A. Tretiakov, H. T. Diep, G. Zhao, J. Yang, Y. Zhou, M. Ezawa, and X. Liu
Journal Info: J. Magn. Soc. Jpn., 47, pp.20-27 (2023).

2023.09.20
The following oral presentation was given by our group member in The 84th Japanese Society of Applied Physics (JSAP) Autumn meeting 2023 (Kumamoto-jo castle Hall, Kumamoto, Japan)

Numb.: 20a-A303-4
Title: Proposal of a mathematical model of amoeba-inspired combinatorial optimization machines for physical inplemantations (in Japanese)
Speakers: Yusuke Miyajima, Masahito Mochizuki

2023.09.15 The following paper has been published online in Advanced Materials. In this paper, by collaboration of experiment and theory, we demonstrated on-demand creations of multiple topological magnetic states such as pairs of meron and antimeron and bimerons (meron pairs), mutual transformation between skyrmions and bimerons, current-induced proliferation of bimerons. Xiuzhen Yu, Naoya Kanazawa, Xichao Zhang, Yoshio Takahashi, Konstantin V. Iakoubovskii, Kiyomi Nakajima, Toshiaki Tanigaki, Masahito Mochizuki, Yoshinori Tokura Advanced Materials adma.202306441 (2023). 題名：Spontaneous Vortex-Antivortex Pairs And Their Topological Transitions in A Chiral-Lattice Magnet

2023.09.16-19
The following oral presentations were given by our group members in The Physical Society of Japan (JPS) 2023 Annual meeting (Aobayama・Kawauchi Campuses, Tohoku University, Sendai, Japan)

Numb.: 17aB102-8
Title: Theoretical study of helical magnetic engineering in chiral magnetic materials (in Japanese)
Speakers: Masaki Tanabe, Masahito Mochizuki

Numb.: 18aC200-5
Title: Topological magnons in the quadruple-Q magnetic hedgehog lattices (in Japanese)
Speakers: Rintaro Eto, Masahito Mochizuki

Numb.: 16pB202-11
Title: Proposal of a computational model of amoeba-inspired combinatorial optimization machines:Towards physical implementations (in Japanese)
Speakers: Yusuke Miyajima, Masahito Mochizuki

2023.08.24
Prof. Cyrill B. Muratov (Universitá di Pisa, Italy) and Dr. Anne Bernand-Mantel（Université de Toulouse, France) visited us in Waseda University. Dr. Anne Bernand-Mantel gave a seminar lecture[Abstract], [Album].

Date：2023.08.24(Thu.) 10:15-
Title：Theory of magnetic field-stabilized compact skyrmions in thin film ferromagnets
Speaker：Dr. Anne Bernand-Mantel（Université de Toulouse, LPCNO, France）
2023.08.21-22
The following presentations were given by our group members in the workshop on the strongly correlated electron systems [web] held in August 21-22 at Sakata-Hirata Hall, Higashiyama campus, Nagoya University, Japan.

[Invited talk]
Title：Optical responses and photo-induced phase transitions in spin-charge coupled magnets (in Japanese)
Speaker: Masahito Mochizuki

[Poster presentation]
Title: Machine-Learning detection of the Berezinskii-Kosterlitz-Thouless transitions and second-order transitions in two-dimensional spin models (in Japanese)
Speaker: Yusuke Miyajima (D2)

Title： Weyl nodal magnons in magnetic 4Q hedgehog lattices (in Japanese)
Speaker: Rintaro Eto (D1)

2023.08.09 The following paper was published in Physical Review B. In this paper, we demonstrate using micromagnetics simulations that the configurations of magnetic domains in the notched ferromagnetic nanotrack can be switched between a head-to-head state and a tail-to-tail state in a reversible manner by application of magnetic-field pulses even without reversing the direction of the magnetic field. Xichao Zhang, Jing Xia, Oleg A. Tretiakov, Guoping Zhao, Yan Zhou, Masahito Mochizuki, Xiaoxi Liu, Motohiko Ezawa Phys. Rev. B 108, 064410/1-11 (2023). Title：Reversible magnetic domain reorientation induced by magnetic field pulses of fixed direction

2023.07.25
Rintaro Eto（D1）gave a poster presentation at the 11th International Symposium on Metallic Multilayers (MML2023) held in July 24-28 at Korea University in Seoul, Korea.

Title：Spin-charge Decoupling in the Low-energy Excitations of Skyrmion Crystals in Kondo-lattice Magnets
Authors：R. Eto, M. Mochizuki

2023.07.19
Prof. Mochizuki gave an invited talk at the 13th International Conference on Metamaterials, Photonic Crystals and Plasmonics (META2023) held in July 18-21 at Ecole Nationale Supérieure d'Arts et Métiers (ENSAM), Paris Campus in Paris, France.

Title：Creation, Manipulation and Switching of Topological Magnetisms in Spin-Charge Coupled Magnets

2023.07.13 The following paper was published in Journal of the Physical Society of Japan. In this paper, we theoretically propose and demonstrate a physical mechanism for the emergence of complex spin textures, including topological ones, with spatial structure of local polarizations in magnets with spatial inversion symmetry, through the spin-lattice coupling via the Dzyaloshinskii-Moriya interactions as well as electric and magnetic dipole interactions. Tatsuki Muto, Masahito Mochizuki Journal of the Physical Society of Japan 92, 084704/1-7 (2023). Title：Theory of Magnetic Vortex Crystals Induced by Electric Dipole Interactions

2023.07.07
Prof. Mochizuki gave an invited talk at the 4th International Symposium on Negative Thermal Expansion and Related Materials (ISNTE-4) held in July 5-7 at Giove Convention Centre of the Best Western Plus Hotel Galileo in Padova, Italy.

Title：Theory of magnetism-induced negative thermal expansion in inverse perovskite antiferromagnets

2023.06.28 The following paper was published in Physical Review B. In this paper, we theoretically propose a method to generate novel topological magnetic structures called skyrmion bags in a nanodisc of chiral magnet by magnetic-field application and local current injection. Lan Bo, Rongzhi Zhao, Chenglong Hu, Xichao Zhang, Xuefeng Zhang, Masahito Mochizuki Physical Review B 107, 224431/1-7 (2023). Title：Controllable creation of skyrmion bags in a ferromagnetic nanodisk

2023.06.19, 2023.06.20
Prof. Mochizuki and R. Eto (PhD student, D1) gave oral presentations at the 7th edition of the Sol-SkyMag International Conference (Sol-SkyMag2023) held in June 19-23 at Carlos Santamaría Library Conference Hall in San Sebastian (Gizpoka), Spain [Album].

2023.06.19
Title：Goldstone excitations with spin-charge separation in skyrmion crystals in Kondo-lattice systems
Speaker：Rintaro Eto

2023.06.20
Title：Thermoelectric effect of magnetic skyrmions
Speaker：Masahito Mochizuki


2023.06.12
Prof. Oleg Tretiakov（University of New South Wales (UNSW), Sydney) visited our group [Album].

2023.06.07
Prof. Mochizuki gave an invited talk at the 9th International Conference on Anntenas and Electromagnetic Systems (AES2023) held in June 4-8 at Palacio de Congresos in Torremolinos, Spain.

Title：Electromagnon Excitations and Microwave/Optical Device Functions in Multiferroic Materials

2023.05.31
Prof. Dr. Mathias Kläui (Johannes Gutenberg University Mainz, Germany) gave a seminar talk[Abstract], [Album].
Date：2023.05.31(Wed.) 15:15
Place：Bldg. 55N(North Tower), 1st floor, 2nd Conference Room, Nishi-Waseda campus, Waseda University
Title：Skyrmions in Spin-Orbitronics and Orbitronics – novel science and applications in memory & non-conventional computing
Speaker：Prof. Dr. Mathias Kläui（Johannes Gutenberg-Universität Mainz, Germany）
2023.05.31
A mini workshop was organized to coincide with Professor Dr. Mathias Kläui's visit. Prof. Dr. Mathias Kläui (Johannes Gutenberg University Mainz, Germany) gave a seminar talk (Special Lecture) [Program], [Album].
Date：2023.05.31(Wed.) 11:30-
Place：Bldg. 55N(North Tower), 1st floor, 2nd Conference Room, Nishi-Waseda campus, Waseda University

2023.05.23 The following book (in Japanese) was published from NTS publishers, Japan. Prof. Mochizuki provided a section contribution about the skyrmions [web],[pamphlet]。 Book title: Spintronics Handbook ―Fundamentals and Applications―(760 pages) ISBN 978-4-86043-842-5, e-Book ISBN 978-4-86043-843-2

2023.05.18
Mu-Kun Lee (Lecturer) gave an oral presentation at IEEE INTERMAG 2023 [web] held in May 15-19 at Sendai International Center in Sendai, Japan.
Title：Reservoir Computing with Spin Waves in a Skyrmion Crystal
Authors：Mu-Kun Lee, Masahito Mochizuki

2023.05.11
Le Zhao (Ph.D student, Tsinghua University, China) gave a seminar talk in our group.
Date: 2023.05.11 (Thur), 14:00
Speaker: Le Zhao（Tsinghua University, China)
Title: Skyrmion Research
Place：Bldg. 55N(North Tower), 1st floor, 2nd Conference Room, Nishi-Waseda campus, Waseda University


2023.05.06
Prof. Mochizuki gave an invited talk at the 8th International Conference on Superconductivity and Magnetism (ICSM2023) held in May 4-11 at Liberty Hotels Lykia in Ölüdeniz, Turkey.

Title：Dynamical Switching, Creation and Manipulation of Topo Magnetism in Spin-Charge Coupled Magnets

2023.04.17 The following paper was published in Physical Review B. In this paper, we propose versatile and powerful machine learning methods for detecting the Berezinskii-Kosterlitz-Thouless transition and the second-order transition in the XXZ model and demonstrate their efficiencies. The XXZ model has three-dimensional spin vectors, which makes it much more difficult to detect phase transitions than the XY and clock models with two-dimensional spin vectors. The proposed methods, called ``temperature identification method" and ``phase classification method", can detect phase transitions in the XXZ model with minimal prior knowledge of the model and prior processing of the data. Y. Miyajima and M. Mochizuki Physical Review B 107, 134420/1-16 (2023). Title：Machine-learning detection of the Berezinskii-Kosterlitz-Thouless transition and the second-order phase transition in XXZ models

2023.04.01
Ryui KANEKO (Research Associate Professor) and Yuya OMINATO（Lecturer at WIAS）joined our group. Tatsuya IGUCHI and Ryo HAMANO also joined as batchelor students. Mu-Kun LI has been promoted to a lecturer.[Member]

2023.03.31
Jean-Baptiste MORÉE (Research Lecturer) and Michael Thobias SCHMID (Research Lecturer) have moved from our group.

2023.03.26
Two students, Yuto Uwabo and Rintaro Eto, have completed their master's degree in the Department of Physics and Applied Physics at Waseda University[Album].

2023.03.26
Two students, Masaki Tanabe and Hirotaka Yano, graduated from the Department of Physics and the Department of Applied Physics, respectively, at Waseda University[Album].

2023.03.26
Rintaro Eto (M2) was selected as a winner of the Koizumi Prize for master's thesis in the Department of Physics and Applied Physics.
[Photo1], [Photo2]

2023.03.26
Rintaro Eto (M2) received the 64th Azusa Ono Memorial Prize for Academic Achievement[Album].

The Azusa Ono Memorial Prize is a student prize established by Waseda University, and is the most prestigious prize among the prizes awarded to students. It was established in 1958 to commemorate the achievements of Azusa Ono, who was a political scientist and worked with Shigenobu Okuma to establish the Tokyo Senmon Gakko, the predecessor of Waseda University.

【Achievement eligible for the award】
R. Eto, R. Pohle, and M. Mochizuki, Phys. Rev. Lett. 129, 017201/1-7 (2022).
Low-Energy Excitations of Skyrmion Crystals in a Centrosymmetric Kondo-Lattice Magnet: Decoupled Spin-Charge Excitations and Nonreciprocity

2023.03.22-25
The following oral presentations were given by our group members in The Physical Society of Japan (JPS) 2023 Spring meeting (Online)
Numb.: 22aC1-3
Title: Machine-Learning Detection of the phase transitions:The second-order transition and the Berezinskii-Kosterlitz-Thouless transition in the two-dimensional classical XXZ models (in Japanese)
Speakers: Yusuke Miyajima, Masahito Mochizuki

Numb.: 23aC2-10
Title: Reservoir Computing with Spin Waves in a Skyrmion Crystal (in English)
Speakers: Mu-Kun Lee, Masahito Mochizuki

Numb.: 23aC2-11
Title: Thiele analysis of the current-induced skyrmion creation and dynamics with the spin-orbit torques (in Japanese)
Speakers: Yuto Uwabo, Masahito Mochizuki

Numb.: 23pE2-5
Title: Theoretical study on photoinduced topological phases in a ferrimagnetism-induced Dirac half-metallic state: Analysis of the periodic Anderson model (in Japanese)
Speakers: Rintaro Eto, Masahito Mochizuki

Numb.: 24pE1-3
Title: Theoretical studies on the photoinduced half-valley metallic phase in α-type organic salt (in Japanese)
Speakers: Keisuke Kitayama, Masao Ogata, Yasuhiro Tanaka, Masahito Mochizuki

2023.03.17
A farewell party was held at Rihga Royal Hotel, Kanshi-so[Album].


2023.03.15-18
The following oral presentation were given by our group members in The 70th JSAP (The Japan Society of Applied Physics) Spring Meeting 2023 (Yotsuya Campus, Sophia University + Online)
Numb.: 16a-D419-9
Title: Theoretical study on controlled creations and dynamics of magnetic skyrmions with the spin-orbit torques (in Japanese)
Speakers: Yuto Uwabo, Masahito Mochizuki

2023.03.13 The following paper was published in a Letter section of Physical Review B. In this paper, we theoretically predicted and demonstrated that by irradiating a skyrmion crystal confined in a circular disk with light or electron beams, we can generate a DC electromotive force in the radial direction from a steady rotational motion in the presence of temperature gradient introduced by the irradiation. This is the world's first proposal of the thermoelectric function of magnetic skyrmions. J. Matsuki and M. Mochizuki Physical Review B 107, L100408 (2023). Title：Thermoelectric effect of a skyrmion crystal confined in a magnetic disk

2023.03.05-10
The following oral presentations were given by our group members in APS March Meeting 2023 (Las Vegas, Nevada, USA).
Numb.: M44.00005 (9:36 AM–9:48 AM, March 8 (Wed), 2023, Room 316)
Title: Dynamical switching of magentic topology in microwave-driven itinerant magnet
Speakers: Rintaro Eto, Masahito Mochizuki

Numb.: W54.00006 (4:24 PM–4:36 PM, March 9 (Thu), 2023, Room 306)
Title: Reservoir Computing with Spin Waves in a Skyrmion Crystal
Speakers: Mu-Kun Li, Masahito Mochizuki

2023.02.19 The following paper was published in npj Quantum Materials. In this paper, we studied the electromagnon excitations in a multiferroic material CuO in collaboration with an experimental group in France. This material exhibits a multiferroic phase near the room temperature. We constructed its microscopic spin model that can quantitatively reproduce the observed multi-step magnetoelectric phase transitions. Using this model, we succeeded in fully reproducing the experimental far-infrared spectra of electromagnon excitations in the multiferroic phase at finite temperatures. M. Verseils, P. Hemme, D. Bounoua, R. Cervasio, J-B. Brubach, S. Houver, Y. Gallais, A. Sacuto, D. Colson, T. Iijima, M. Mochizuki, P. Roy and M. Cazayous npj Quantum Materials　8, 11 (2023). Title：Stabilizing electromagnons in CuO under pressure

2023.02.03
The graduation thesis presentations of the Department of Applied Physics and the Department of Physics were held. Two students from our group, Masaki Tanabe and Hirotaka Yano, gave presentations.

【Bachelor Thesis Titles】
Masaki Tanabe ``Theory of helimagnetism engineering in chiral magnets"
Hirotaka Yano ``Theoretical study on the magnetic phases in a skyrmionic material with a polar tetragonal crystal structure"

2023.02.04
The master's thesis presentations of the Department of Physics and Applied Physics were held. Two students from our group, Yuto Uwabo and Rintaro Eto, gave presentations.

【Mater's Thesis Titles】
Yuto Uwabo ``Theoretical study on the creation and motion of skyrmions driven by the spin-orbit torque"
Rintaro Eto ``Theory of low-energy excitations and photocontrol of topological spin textures in spin-charge coupled magnets"

2023.01.27
Prof. Mochizuki gave an invited talk at the workshop held on January 27 at Tokyo Satellite Campus of Nagaoka University of Technology.

Title：Reservoir-type information processing device utilizing spin-wave propagation in a skyrmion crystal (in Japanese)

2023.01.17
Yusuke Miyajima (PhD student) gave an oral presentation at 2023 Annual Meeting of the Physical Society of Taiwan (TPS2023) held in Taiwan (Jan. 16-18, 2023).

Title: Proposal of a machine learning method for detection of the Berezinskii-Kosterlitz-Thouless transitions in the q-state clock models

2023.01.11
Xichao ZHANG has joined our lab. as a postdoc/research lecturer [Members]. He will work on the JST, CREST research project Creation of a new topological magnetic science for Beyond Skyrmion".

2022.12.24
Prof. Mochizuki gave an invited talk at a workshop about new trends in the chiral materials science held in ISSP, the University of Tokyo (Dec.22-24, 2022).

Title: Chiralities and dynamics in the multiferroics (in Japanese)

2022.12.22
Keisuke Kitayama (Former student member) gave an oral presentation at a winter school for young researchers on organic materials [web] held at Okazaki Conference Center in National Institutes of Natural Sciences (NINS), Okazaki, Aichi, Japan (December 22-23, 2022).

Title: Theoretical studies of photoinduced topological phase transitions in organic salt α-(BEDT-TTF)₂I₃ (in Japanese)

2022.12.19
BO Lan has joined our lab. as a research student [Members]. He is a third-year Ph.D student in the Northeastern university in China. He will stay in our lab for a year as a postgraduate student funded by China Scholarship Council.

2022.12.07
Li Mu-Kun (Postdoc・Research Lecturer) gave an oral presentation at an international workshop ``The Workshop on Innovative Nanoscale Devices and Systems (WINDS2022)" held on the Island of Kaua'i, Hawaii (December 4-9, 2022).

Title: Microwave-Driven Phenomena of Magnetic Skyrmions

2022.11.15
Keisuke Kitayama (Former student member) gave a poster presentation at the YIPQS long-term and Nishinomiya-Yukawa memorial workshop ``Novel Quantum States in Condensed Matter 2022" (NQS2022) held at Yukawa Institute for Theoretical Physics (YITP), Kyoto university, Kyoto, Japan (Oct. 31-Dec. 2, 2022).

Title: Theoretical studies of photoinduced topological phase transitions in organic salt α-(BEDT-TTF)₂I₃

2022.11.02
Prof. Mochizuki gave an oral presentation at an international workshop ``The 67th Annual Conference on Magnetism and Magnetic Materials (MMM2022)" held in Hyatt Regency Minneapolis, MN, USA (Oct.31-Nov.4, 2022).

Title: Microwave-Driven Phenomena of Magnetic Skyrmions

2022.09.29
Keisuke Kitayama (Former student member) gave an oral presentation at an international workshop The 14th International Symposium on Crystalline Organic Metals, Superconductors and Magnets (ISCOM2022)" held in Le Pouliguen, France (September 25-30, 2022).

Title: Theoretical studies of photoinduced topological phase transitions in organic salt α-(BEDT-TTF)₂I₃

2021.09.28
Rintaro Eto (second-year master's student) has been selected as a JSPS Research Fellow DC1 for the coming year.

2021.09.26 The following paper has been published in Journal of the Physical Society of Japan. In this paper, we theoretically predicted possible occurrence of a new-type photoinduced topological phase transition in the organic salt α-(BEDT-TTF)2I3 irradiated by elliptically polarized laser light. We found that a nonequilibrium phase transition from the Floquet Chern-insulator phase to the Floquet normal-insulator phase takes place accompanied by collapse and vanishing of the Dirac points with the same topological magnetic charges when the angle that the elliptical polarization axis makes with the crystallographic axis is 45$^\circ$. K. Kitayama, M. Ogata, M. Mochizuki, and Y. Tanaka, J. Phys. Soc. Jpn. 91, 104704/1-8 (2021). 題名：Predicted novel type of photoinduced topological phase transition accompanied by collision and collapse of Dirac-cone pair in organic salt α-(BEDT-TTF)2I3

2022.09.12-15
The following presentations have been given by our group members in 2022 JPS Autumn meeting (Tokyo Institute of Technology, Ookayama Campus)

Numb.: 12aW241-1
Title: Theoretical study on the photoinduced topological phases in the ferrimagnetism-induced Dirac electron state
Speakers: Rintaro Eto, M. Mochizuki

Numb.: 13aW331-12
Title: Melting of charge order and topological phase transition in organic conductor α-(BEDT-TTF)₂I₃ irradiated with circularly polarized light
Speakers: Yasuhiro Tanaka, M. Mochizuki

Numb.: 13aW641-2
Title: Theoretical study of magnetic vortex crystals induced by electric dipole interactions
Speakers: Tatsuki Muto, M. Mochizuki

Numb.: 13aW641-5
Title: Theoretical study of magnetic phase transitions and electromagnon excitations in multiferroic CuO
Speakers: Takaaki Iijima, M. Mochizuki

Numb.: 13pW641-2
Title: Theoretical study on creations and manipulations of magnetic skyrmions with the spin-orbit torque
Speakers: Yuto Uwabo, M. Mochizuki

Numb.: 14pW541-6
Title: Theoretical study on the collective spin excitations of quadruple-Q magnetic hedgehog lattices
Speakers: Rintaro Eto, M. Mochizuki

Numb.: 14pW641-7
Title: Theoretical study on thermoelectric effect of magnetic skyrmion crystal confined in a disk-shaped system
Speakers: Junnosuke Matsuki, M. Mochizuki

2022.09.10
The following symposium talk has been given by Mochizuki in the Symposium on ``Spin quantum phenomena driven by light and terahertz" in 2022 JPS Autumn meeting (Tokyo Institute of Technology, Ookayama Campus)

Title: Theory of optical manipulations of magnetisms (10aS2-3)

2022.08.22
Keisuke Kitayama (Former student member) gave an oral presentation at an international workshop ``The 29th International Conference on Low Temperature Physics (LT29)" held at Sapporo Convention Center, Sapporo, Hokkaido, Japan (August 18-24, 2022).

Title: Theoretical studies of photoinduced topological phase transitions in organic salt α-(BEDT-TTF)₂I₃

2022.07.29 The following paper has been published in Physical Review Applied. In this paper, we theoretically demonstrated that spin-waves propagating in a magnetic skyrmion crystal confined in thin-plate magnets have high potential for application to reservoir-computing devices. We numerically examined several characteristics required for reservoir computings for the skyrmion spin-wave reservoir, i.e., the generalization ability, the short-term memory, and the nonlinearlity by imposing the duration estimate task, the short-term memory task, and the parity check task, respectively, and revealed that the skyrmion spin-wave reservoirs possess high figures of merits for these characteristics. This paper was selected as an Editors' Suggestion. M-K. Lee, and M. Mochizuki, Phys. Rev. Applied 18, 014074 (2022).Editors' Suggestion Title: Reservoir Computing with Spin Waves in a Skyrmion Crystal

2022.07.26
A visiting Ph.D student from Ibaraki University, Keisuke Masuda, joined our group. He will stay for a month [Member].

2022.07.21
An article (in Japanese) about our theoretical studies on the photoinduced phase transitions in α-(BEDT-TTF)₂I₃ was published in Kotaibutsuri journal.

M. Mochizuki, K. Kitayama, Y. Tanaka, M. Ogata
Kotaibutsuri Vol. 57, Issue 7 (2022.07.「Topics」) pp. 1(397)-13(409).

Title: Theoretical studies on the photoinduced topological phase transitions in an organic salt α-(BEDT-TTF)₂I₃

2022.07.21
The following invited talk has been given by Mochizuki in the 12th International Conference on Metamaterials, Photonic Crystals and Plasmonics (META2022, Spain, Torremolinos).

Title: Dynamical Magnetic Phase Transitions in Spin-Charge Coupled Systems

2022.07.18 The following paper has been published in Physical Review Letters. In this paper, we theoretically studied the photoinduced phase transitions in a typical strongly correlated Dirac electron system α-(BEDT-TTF)2I3 irradiated with circularly polarized light. By analyzing an extended Hubbard model with on-site and inter-site Coulomb repulsive interactions using a newly developed theoretical framework which combines real-time dynamics simulations and the Foquet theory, we revealed successive photoinduced phase transitions from the ground-state charge-ordered insulator via the Dirac semimetal to the Chern insulator and its microscopic mechanisms associated with dynamical variations of electronic structures. Y. Tanaka, and M. Mochizuki, Phys. Rev. Lett. 129, 047402/1-6 (2022). Title: Dynamical phase transitions in the photodriven charge-ordered Dirac-electron system

2022.07.13
The following invited talk has been given by Mochizuki in the 24th International Colloquium on Magnetic Films and Surfaces (ICMFS-2022, OIST, Okinawa, Japan).

Title: Dynamical Phenomena of Magnetic Skyrmions

2022.06.28 The following paper has been published in Physical Review Letters. In this paper, we numerically studied low-energy excitations of magnetic skyrmion crystals in the Kondo-lattice model on a triangular lattice with spatial inversion symmetry and discovered two Goldstone modes associated with charge and spin degrees of freedom and their perfect segregation. Our finding indicates that the charges and spins can be excited separately and selectively in the skyrmion crystals stabilized by interactions mediated by conduction electrons in centrosymmetric magnets. R. Eto, R. Pohle, and M. Mochizuki, Phys. Rev. Lett. 129, 017201/1-7 (2022). Title: Low-Energy Excitations of Skyrmion Crystals in a Centrosymmetric Kondo-Lattice Magnet: Decoupled Spin-Charge Excitations and Nonreciprocity

2021.09.17.
Condensed-Matter Theory Seminar (in-person).
Date&Time: 2022.06.17 (Fri.) 14:00
Speaker: Prof. Oleg Tretiakov（(University of New South Wales (UNSW), Sydney)
Title: Nucleation and dynamics of magnetic solitons in topological materials

2022.04.19 The following paper has been published in Physical Review B. In this paper, we theoretically predict a possible photoinduced magnetic phase transition from the ferromagnetism to the 120-degree spin order in the Kondo-lattice model on a triangular lattice. A pseudo half-filled electronic structure turns out to stabilize the 120-degree order, which is realized via electron excitations, dynamical localizations, gap opening, relaxations, and reconstruction of the electronic structure under irradiation with light. This work demonstrates that the light irradiation can induce a noncollinear magnetic state as a nonequilibrium steady phase via the general mechanism. T. Inoue, and M. Mochizuki, Phys. Rev. B 105, 144422 (2022). Photoinduced 120-degree spin order in the Kondo-lattice model on a triangular lattice

2022.03.18
The following symposium talk has been given by Mochizuki in a symbosium of the 77th JPS annual meeting.

Numb.: 18pS11-6
Title: Photoinduced topological phase transitions in the α-type organic salt (Theory)

2021.12.22-23
The following invited talk has been given by Mochizuki in the international conference on "Frustration, Topology and Spin Textures" (Kobe, Japan).

Title: Dynamical manipulations of topological magnetism with light and microwave electromagnetic fields

2021.12.22-23
The following poster presentations has been given by our group in the international workshop on "Frustration, Topology and Spin Textures" (Kobe, Japan).

Title: Theory of optical spin-polarization induction in Rashba spin-orbit electron systems
Presenters: Yasuhiro Tanaka, Takashi Inoue, Masahito Mochizuki

Title: Photoinduced 120-degree spin order and Z₂ vortices in the Kondo-lattice model on a triangular lattice
Presenters: Takashi Inoue, Masahito Mochizuki

Title: Machine learning detection of multiple phase transitions including BKT transition in the q-state clock models
Presenters: Yusuke Miyajima, Masahito Mochizuki

Title: Theoretical Exploration of Magnetism-Induced Negative Thermal Expansion in Honeycomb-Lattice Antiferromagnets
Presenters: Yuto Uwabo, Masahito Mochizuki

Title: Spin and Charge Excitations of Skyrmion Crystals in Itinerant Magnet
Presenters: Rintaro Eto, Rico Pohle, Masahito Mochizuki


2021.12.15
Mochizuki gave an invited talk in RIKEN Institute.

Title: Reservoir computing with spin waves in magnetic skyrmion crystal

2021.12.01-02
Our members, Y. Tanaka, M. Naka, and K. Kitayama, gave presentations in the ISSP workshop on novel materials and phenomena of orgaic compounds (Kashiwa, Japan).

2021.10.30
Rico Pohle has moved to Prof. Motome's group in Univ. of Tokyo.

2021.10.20
The following invited talk has been given by Mochizuki in the international conference on ``Condensed Matter Physics (CONMAT2021)" (online).

Title: Theory of Magnetism-Induced Negative Thermal Expansion in Inverse Perovskite Antiferromagnets

2021.09.27 The following paper has been published in Physical Review B. In this paper, we theoretically predict and reveal possible magnetic-topology switching among skyrmion crystals with different topological numbers and nontopological magnesitms by irradiating centrosymmetric Kondo-lattice magnets on a triangular lattice with circularly polarized microwave magnetic fields. In transient processes of these microwave-induced topology switchings, we observe several distinct behaviors of dynamical phase transitions as well as emergence of peculiar topological magnetisms called meron crystals charcterized by skyrmion numbers of half integers. R. Eto, and M. Mochizuki, Phys. Rev. B 90, 104425 (2021). Title: Dynamical switching of magnetic topology in microwave-driven itinerant magnet

2021.09.24 The following paper has been published in Journal of the Physical Society of Japan. In this paper, we theoretically propose possible realization of the negative thermal expansion in the honeycomb-lattice antiferromagnets composed of edge-sharing MX6 octahedra (M and X represent transition-metal ions and ligand ions, respectively). In contrast to normal materials, crystal volumes of these kinds of magnets are expected to expand upon cooling, which is triggered by the antiferromagnetic phase transition. Y. Uwabo, and M. Mochizuki, J. Phys. Soc. Jpn. 90, 104712 (2021). Title: Proposed Negative Thermal Expansion in Honeycomb-Lattice Antiferromagnets

2021.09.20-23
The following presentations have been given by our members in 2021 JPS Autumn meeting (online)

Numb.: 20aC1-4
Title: Theoreticalstudyonthedynamicsofmagnetictexturesinitineranthelicalmagnets
Speakers: R. Eto, Rico Pohle, M. Mochizuki

Numb.: 21pE1-7
Title: Topological state induced by circularly polarized light in organic conductor
Speakers: Y. Tanaka, M. Mochizuki

Numb.: 22aC1-5
Title: Theoretical Exploration of Negative Thermal Expansion in Honeycomb Lattice Transition Metal Compounds
Speakers: Y. Uwabo, M. Mochizuki

Numb.: 22pL4-3
Title: Detection of the Kosterlitz-Thouless transitions by machine learning
Speakers: Y. Miyajima, Y. Murata, Y. Tanaka, M. Mochizuki

Numb.: 23pH3-5
Title: Theoretical study of the Dirac-point pair annihilation and topological phase transitions in the α-type organic salt induced by elliptically polarized light
Speakers: K. Kitayama, Y. Tanaka, M. Ogata, M. Mochizuki

2021.09.17.
The 5th Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.09.17 (Thu.) 16:00
Speaker: Lan Bo (Northeastern University, P. R. China)
Title: Micromagnetic Behaviors of Magnetic Topological Solitons [Abstract]

2021.09.15 The following paper has been published in Journal of the Physical Society of Japan. In this paper, we reveal entire behaviors of photoinduced topological phase transitions in the organic salt α-(BEDT-TTF)2I3 with a pair of tilted Dirac-cone dispersions theoretically using the Floquet thoery. Irradiation by elliptically polarized light give rise to quite rich nonequilibrium phase diagrams containing photoinduced Chern insulator phases. (Selected as Editors' Choice) K. Kitayama, Y. Tanaka, M. Ogata, and M. Mochizuki J. Phys. Soc. Jpn. 90, 104705 (2021).Editors' Choice Title: Floquet theory of photoinduced topological phase transitions in the organic salt α-(BEDT-TTF)2I3 irradiated with elliptically polarized light

2021.08.16 The following paper has been published in Physical Review B. In this paper, we theoretically reveal that irradiation by linearly polarized light can induce a pair annihilation of emergent topological magnetic charges with opposite signs in the momentum space of an organic salt α-(BEDT-TTF)2I3, in which a pair of tilted Dirac-cone bands are slightly gapped due to weak charge dispropotionation. This is a theoretical prediction of monopole-antimonopole pair annihilation of 2D version can be realized by photoirradiation in the momentum space of crystalline materials. K. Kitayama, M. Mochizuki, Y. Tanaka, and M. Ogata Phys. Rev. B 104, 075127 (2021). Title: Predicted photoinduced pair annihilation of emergent magnetic charges in the organic salt α-(BEDT-TTF)2I3 irradiated by linearly polarized light

2021.08.13 The following paper has been published in Physical Review B. In this paper, we theoretically clarify the real-time dynamics of photoinduced topological phase transitions in an organic salt α-(BEDT-TTF)2I3 with tilted Dirac-cone band dispersions under irradiation with circularly polarized light. It is revealed that spatiotemporal dynamics characterized of different three time scales appear, which are, respectively, governed by the light frequency, the averaged magnitude of gaps at the Dirac points, and the difference of gap amplitudes between the two Dirac points under application of an electric field. Y. Tanaka and M. Mochizuki, Phys. Rev. B 104, 085123 (2021). Title: Real-time dynamics of the photoinduced topological state in organic conductor α-(BEDT-TTF)2I3 under continuous-wave and pulse excitations

2021.08.11 The following paper has been published in Physical Review B. In this paper, we demonstrate that a machnie learning is capable of detecting successive Berezinskii-Kosterlizt-Thouless transitions in the n-state clock models. Introducing a new correlation function to the heat-map anlyses, we quantitatively determine the BKT transition points. Y. Miyajima, Y. Murata, Y. Tanaka, and M. Mochizuki, Phys. Rev. B 104, 075114 (2021). Title: Machine learning detection of Berezinskii-Kosterlitz-Thouless transitions in q-state clock models

2021.07.22
The 4th Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.07.22 (Thu.) 15:00
Speaker: Rubén M. Otxoa (Hitachi Cambridge Laboratory)
Title: Topological energy release from collision of relativistic antiferromagnetic solitons[Abstract]


2021.07.20
Invited talk in the international conference ``The 11th International Conference on Metamaterials, Photonic Crystals and Plasmonics (META 2021)".

SpeakerM. Mochizuki
Title: Theory of Photoinduced Spin Polarization in Spin-Orbit-Coupled Systems

2021.07.01
Dr. Collins Ashu AKOSA joined our group as a postdoc researcher (project lecturer) of the JST-CREST project.

2021.05.31
Ms. Yoko Takahashi (Secretary) retired.

2021.06.01
The 3rd Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.06.01 (Thu.) 16:00
Speaker: Yuya Ominato (KITS, UCAS, P. R. China)
Title: Spin transport phenomena in atomic layer materials [Abstract]


2021.05.26
The 2nd Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.05.26 (Wed.) 16:30
Speaker: Atsushi Ono (Tohoku university)
Title: Photoinduced spin-scalar-chiral states in triangular-lattice itinerant magnets [Abstract]


2021.05.25
The 1st KIBAN-A meeting (online).
[Program]

2021.05.24
The 1st Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.05.24 (Mon.) 13:30
Speaker: Shunsuke Furuya (Ibaraki university)
Title: DC electric-field controls of superexchange and Dzyaloshinskii-Moriya interactions in Mott insulators [Abstract]


2021.05.18
Rintaro Eto gave a talk on an online seminar in Motome group, Department of Applied Physics, the University of Tokyo.

2021.06.01
The 3rd Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.06.01 (Thu.) 16:00
Speaker: Yuya Ominato (KITS, UCAS, P. R. China)
Title: Spin transport phenomena in atomic layer materials [Abstract]


2021.05.26
The 2nd Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.05.26 (Wed.) 16:30
Speaker: Atsushi Ono (Tohoku university)
Title: Photoinduced spin-scalar-chiral states in triangular-lattice itinerant magnets [Abstract]


2021.05.25
The 1st KIBAN-A meeting (online). [Program]

2021.05.24
The 1st Condensed-Matter Theory Seminar (online) in FY2021.

Date&Time: 2021.05.24 (Mon.) 13:30
Speaker: Shunsuke Furuya (Ibaraki university)
Title: DC electric-field controls of superexchange and Dzyaloshinskii-Moriya interactions in Mott insulators [Abstract]


2021.05.18
Rintaro Eto (M1 student) gave a talk on an online seminar in Motome group, Department of Applied Physics, the University of Tokyo.