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New! 2025. 12. 4

By developing a high-sensitive ultrafast time-resolved magneto-optical microscope, we succeeded in the observation of current-pulse induced magnetization switching in a topological antiferromagnet Mn₃Sn in a 100-ps time scale. We revealed that the switching mechanism changes from a non-thermal to a thermal process depending on the magnitude of the applied current density.The result provides the proof of principle towards ultrafast magnetization switching in an antiferromagnet.
This work has been published in Nature Materials.
[Nature Materials, DOI:10.1038/s41563-025-02402-8]
A press release on the same content has also been issued.

• Press Releases, School of Science

2025. 11. 4

Project Assist. Prof. Fumiya Sekiguchi received Young Scientist Award of the Physical Society of Japan.

2025. 09. 09

Paper: "On-Chip Terahertz Pump–Probe Spectroscopy Revealing Ultrafast Current-Induced Breakdown Dynamics in a Superconducting Nb Microstrip" has been published in Nano Letters.
[Nano Letters 25, 13764 (2025).]

2025. 08. 18

Paper: "Distinct terahertz nonlinear and Raman responses in cuprate superconductors Bi₂Sr₂CaCu₂O_8+x has been published in npj Quantum Materials.
[npj Quantum Materials 10, 91 (2025).]

2025. 06. 02

We have experimentally demonstrated anomalous Hall conductivity arising from the Floquet state in the three-dimensional Dirac semimetal Co₃Sn₂S₂. Upon illumination with circularly polarized light that breaks time-reversal symmetry, we observed an instantaneous anomalous Hall response. The dependence of the anomalous Hall conductivity on electric field strength and driving frequency was found to be consistent with theoretical calculations based on Floquet theory, which attribute the response to band structure modification and induced Berry curvature. The estimated band splitting reached approximately 60% of the Dirac gap, highlighting the potential of this approach as a new route to create a Weyl semimetal state using light.
This work was published in Physical Review B and selected as an Editors’ Suggestion.
[Phys. Rev. B 111, 245104 (2025).]

2025. 03. 10

Daichi Yoshioka received "The School of Science Encouragement Award AY2024".

2025. 02. 17

Kotaro Tanaka and Naotaka Yoshikawa received Best Poster Award at The 16th Research Forum of Cryogenic Research Center.

2024. 12. 19

Paper: "Emergence of light-induced superconducting-like state from the charge density wave state in high-𝑇_c cuprate superconductors has been published in Physical Review B.
[Phys. Rev. B 110, 224515 (2024).]
The paper is selected as Editors' suggestion and also featured by SYNOPSIS in Physics Magazine.
See also, [Physics Magazine, SYNOPSIS "Making Waves in the Debate over Light-Induced Superconductivity"]

2024. 07. 19

Picosecond trajectory of two-dimensional motion of quantized vortices in an iron-based superconductor is visualized by observing the second-harmonic generation in the terahertz frequency range. The vortex’s effective mass becomes as light as bare electron mass under such an ultrafast motion, which suggests that the vortex core moves independently from quasiparticles at such a high frequency and large velocity ≈300  km/s.
[Phys. Rev. Lett. 133, 036004(2024).]
The paper is selected as Editors' suggestion and also featured by FOCUS in Physics Magazine.
See also, [Physics Magazine, FOCUS "Viewing Fast Vortex Motion in a Superconductor"]

2024. 03. 18

Yoshua Hirai received "The School of Science Encouragement Award AY2023".

2024. 02. 16

Yoshua Hirai received Best Poster Award at The 15th Research Forum of Cryogenic Research Center.

2024. 02. 09

We theoretically demonstrated that Floquet-Weyl states, possessing a topological charge of ±2, emerge universally at one-photon resonances in three-dimensional Dirac electrons when resonantly driven by circularly polarized light.
[Phys. Rev. Research 6, L012027 (2024).]

2023. 09. 01

We developed a time-resolved magneto-optical microscope and succeeded in visualizing domain wall motion induced by current pulses in ferrimagnetic materials in sub-ns time scale.
[Phys. Rev. Research 5, 033151 (2023).]

2023. 06. 08

We investigated the light-induced nonequilibrium state in an underdoped YBa₂Cu₃O_y sample with T_C of 61 K using the nonlinear THz optical response originating from the superconducting collective excitation of the ac-driven Josephson current.
[Phys. Rev. B 107, 214506 (2023).]

2023. 05. 26

Paper: "Light-induced coherent interlayer transport in stripe-ordered La_1.6−xNd_0.4Sr_xCuO₄" has been published in Physical Review B.
[Phys. Rev. B 107, 174523 (2023).]

2023. 03. 23

Kazuma Ogawa received "The School of Science Encouragement Award AY2022".

2023. 02. 16

Haruki Matsumoto and Ushio Narusaka received Best Poster Award at The 14th Research Forum of Cryogenic Research Center.

2022. 12. 20

Paper: "Non-volatile chirality switching by all-optical magnetization reversal in ferromagnetic Weyl semimetal Co₃Sn₂S₂" has been published in Communications Physics. By irradiating mid-infrared circularly polarized light, the chirality of the Weyl nodes in Co₃Sn₂S₂ is reversed via all-optical magnetization switching due to the intimate coupling between the chirality and magnetization in the magnetic Weyl semimetal.
[Commun. Phys. 5, 328 (2022).]

2022. 10. 26

Assist. Prof. Naotaka Yoshikawa received Young Scientist Award of the Physical Society of Japan.

2022. 04. 05

Paper: "Optical response of the Leggett mode in multiband superconductors in the linear response regime" has been published in Physical Review B.
[Phys. Rev. B 105, 094520 (2022).]

2022. 01. 14

Paper: "Terahertz pulse-driven collective mode in the nematic superconducting state of Ba_1−xK_xFe₂As₂" has been published in npj Quantum Materials.
[npj Quantum Materials 7, Article number: 4 (2022).]

2021. 07. 14

Paper: "Light-induced enhancement of superconductivity in iron-based superconductor FeSe_0.5Te_0.5" has been published in Communications Physics. The enhancement of the superconducting order parameter upon the light pulse illumination is revealed through the optical conductivity and third harmonic generation measurement in the terahertz frequency range. This result suggests the potential tunability of the pairing interaction by light in the ultrafast timescale.
[Commun. Phys. 4, 160 (2021).]

2021. 07. 14

The paper reporting the ultrafast transition from a metallic to insulating-like state when a two-dimensional material is irradiated by terahertz pulses was introduced in Phys.Org.

2021. 06. 29

Paper: “Ultrafast switching to an insulating-like metastable state by amplitudon excitation of a charge density wave” has been published in Nature Physics. We discovered that a hidden ordered insulating-like state is induced from a preexisting metallic charge density wave phase in 3R-TaSe₂ upon the resonant excitation of amplitude mode of the charge density wave by terahertz pulse.
[Nature Physics 17, 909 (2021).] [News & Views]

2021. 04. 16

Paper: “Switchable generation of azimuthally- and radially-polarized terahertz beams from a spintronic terahertz emitter” has been published in Optics Express. We succeeded in demonstrating a method for switchable generation of THz radial and azimuthal beam, where a topological vortex nature appears in its polarization state, using a spintronic emitter.
[Optics Express 29, 13331 (2021).]
The paper was also selected as an Editors' Pick.

2020. 12. 04

Paper: “Terahertz Emission from Bismuth Thin Films Induced by Excitation with Circularly Polarized Light” has been published in Physical Review Applied. We discovered that terahertz radiation is efficiently emitted from thin films of the semimetal Bi, a Dirac electron system, by irradiating it with circularly polarized light pulses. It is interpreted that the terahertz radiation is caused by the combination of spin polarization generation at the sample's surface by circularly polarized light, spin current generation by diffusion, and its conversion into a current pulse by the inverse spin Hall effect. Our findings open a new route to simple and compact methods for generating terahertz wave pulses and also for the ultrafast control of spin current.
[Phys. Rev. Appl. 14, 064015 (2020).]
The paper was also selected as an Editors' suggestion.

2020. 08. 29

Paper: "Nonreciprocal Terahertz Second-Harmonic Generation in Superconducting NbN under Supercurrent Injection" has been published in Physical Review Letters. The paper demonstrates a giant nonreciprocal second-harmonic generation in the terahertz (THz) frequency range in a thin film of an s-wave superconductor NbN, where the time-reversal ($\mathscr{T}$) and space-inversion ($\mathscr{P}$) symmetries are simultaneously broken by supercurrent injection. The microscopic origin of the observed THz nonlinear response is ascribed to the vortex motion driven by the THz electric field in an anharmonic pinning potential.
[Phys. Rev. Lett. 125, 097004 (2020).]

2020. 08. 14

Paper: "Superconducting fluctuations probed by the Higgs mode in Bi₂Sr₂CaCu₂O_8+x thin films" has been published in Physical Review B. We have revealed two onset temperatures of the THz nonlinear response in cuprate superconductors, Bi₂Sr₂CaCu₂O_8+x. The first one (T₁^ons) is located 10–30 K above the superconducting critical temperature (T_c) and interpreted as an onset temperature of the superconducting phase coherence. The second one (T₂^ons) is identified at substantially higher than T_c whose origin is discussed in terms of preformed Cooper pairs.
[Phys. Rev. B 102, 054510 (2020).]

2020. 04. 15

Paper: "Phase-resolved Higgs response in superconducting cuprates" has been published in Nature Communications.
[Nature Communications 11, 1793 (2020).]

2020. 03. 23

Yuta Murotani received Research Incentive Award (Doctor Course), Graduate School of Science, The University of Tokyo.

2019. 12. 16

Assist. Prof. Naotaka Yoshikawa received Inoue Research Award for Young Scientists.

2019. 11. 08

Paper: "Light-driven electron-hole Bardeen-Cooper-Schrieffer-like state in bulk GaAs" has been published in Physical Review Letters.
[Phys. Rev. Lett. 123, 197401 (2019).]
The paper was also selected as an Editors' Suggestion.

2019. 10. 07

Review article: "Higgs mode in Superconductors" has been posted online in Annual Review of Condensed Matter Physics (advanced online version).
[Annual Review of Condensed Matter Physics Volume 11, 2020 (in Advance first posted online).]

2019. 09. 05

Paper: "Light-induced nonequilibrium response of the superconducting cuprate La_2−xSr_xCuO₄" has been published in Physical Review B.
[Phys. Rev. B 100, 104507 (2019).]
The paper was also selected as an Editors' Suggestion.

2019. 07. 13

Paper: "Charge carrier dynamics of FeSe thin film investigated by terahertz magneto-optical spectroscopy" has been published in Physical Review B.
[Phys. Rev. B 100, 035110 (2019).]

2019. 06. 26

Paper: "Infrared Activation of the Higgs Mode by Supercurrent Injection in Superconducting NbN" has been published in Physical Review Letters.
[Phys. Rev. Lett. 122, 257001 (2019).]

2019. 06. 21

Kota Katsumi received Young Researchers Award at Spectroscopies in Novel Superconductors 2019.

2019. 06. 17

Paper: "Nonlinear optical response of collective modes in multiband superconductors assisted by nonmagnetic impurities" has been published in Physical Review B.
[Phys. Rev. B 99, 224510 (2019).]

2018. 03. 22

Kota Katsumi received Research Incentive Award (Master Course), Graduate School of Science, The University of Tokyo.

2018. 03. 14

Paper: "Higgs mode in the d-wave superconductor Bi₂Sr₂CaCu₂O_8+x driven by an intense terahertz pulse" has been published in Physical Review Letters.
[Phys. Rev. Lett. 120, 117001 (2018).]
The paper was also selected as an Editors' Suggestion.

2018. 03. 09

Paper: "Ultrafast terahertz nonlinear optics of Landau level transitions in monolayer graphene" has been published in Physical Review Letters.
[Phys. Rev. Lett. 120, 107401 (2018).]

2018. 02. 21

Masayuki Takayama received Best Poster Award at The 9th Research Forum of Cryogenic Research Center.

2018. 02. 21

Paper: "Terahertz field-induced ionization and perturbed free induction decay of excitons in bulk GaAs" has been published in Journal of Physics D: Applied Physics.
[J. Phys. D: Appl. Phys. 51, 114001 (2018).]

2018. 01. 01

Dr. Naotaka Yoshikawa joined in our laboratory as Assistant Professor.

2017. 09. 20

Paper: "Rate Equation Analysis of the Dynamics of First-order Exciton Mott Transition" has been published in Journal of the Physical Society of Japan.
[J. Phys. Soc. Jpn. 86, 103702 (2017).]

2017. 07. 21

Paper: "Polarization-resolved terahertz third-harmonic generation in a single-crystal superconductor NbN: Dominance of the Higgs mode beyond the BCS approximation" has been published in Physical Review B Rapid Communications.
[Phys. Rev. B 96, 020505(R) (2017).]

2017. 07. 01

Assist. Prof. Ryusuke Matsunaga was promoted to Associate Professor at Institute of Solid State Physics, The University of Tokyo.

2017. 02. 07

Paper: "Anomalous metal phase emergent on the verge of an exciton Mott transition" has been published in Physical Review Letters.
[Phys. Rev. Lett. 118, 067401 (2017).]

2017. 01. 01

Dr. Fumiya Sekiguchi moved to the University of Cologne, Germany, as a postdoctoral researcher.

2016. 06. 03

Kaito Tomari received Best Poster Award at International Conference on Low-Energy Electrodynamics in Solids 2016.

2016. 03. 24

Fumiya Sekiguchi received Research Incentive Award (Doctor Course), Graduate School of Science, The University of Tokyo.

2016. 02. 04

Prof. Shimano received Inoue Prize for Science.

2015. 04. 06

Paper: "Excitonic correlation in the Mott crossover regime in Ge" has been published in Physical Review B.
[Phys. Rev. B 91, 155202 (2015).]

2014. 09. 05

Paper: "Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor" has been published in Science.
[Science 345, 1145 (2014).]

2014. 07. 11

Paper: "Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor" has been published online in Science Express.
[Science (2014) DOI: 10.1126/science.1254697.]

2013. 07. 29

Paper: "Higgs Amplitude Mode in the BCS Superconductors Nb_1-xTi_xN induced by Terahertz Pulse Excitation" has been published in Physical Review Letters.
[Phys. Rev. Lett. 111, 057002 (2013).]

2013. 05. 14

Paper: "Quantum Faraday and Kerr rotations in graphene" has been published in Nature Communications.
[Nature Communications 4, 1841 (2013).]

2012. 10. 31

Paper: "Nonequilibrium BCS state dynamics induced by intense terahertz pulses in a superconducting NbN film" has been published in Physical Review Letters.
[Phys. Rev. Lett. 109, 187002 (2012).]

2012. 07. 26

Paper: "Exciton Mott transition in Si revealed by terahertz spectroscopy" has been published in Physical Review Letters.
[Phys. Rev. Lett. 109, 046402 (2012).]

2012. 04. 20

Our paper [EPL 95, 17002 (2011)] was selected for the EPL Best of 2011 collection.

2011. 12. 16

Assist. Prof. Ryusuke Matsunaga received Inoue Research Award for Young Scientists.

2011. 12. 04

Paper: "Magnetoelectric resonance with electromagnons in a perovskite helimagnet" has been published in Nature Physics.
[Nature Physics 8, 121 (2012).]

2011. 11. 01

Ex-Assist. Prof. Shinichi Watanabe (Assoc. Prof. in Keio University in present) received Young Scientist Award of the Physical Society of Japan.

2011. 06. 14

Paper: "Terahertz Faraday rotation induced by an anomalous Hall effect in the itinerant ferromagnet SrRuO3 " has been published in EPL.
[EPL 95, 17002 (2011).]

2011. 04. 01

Dr. Ryusuke Matsunaga joined in our laboratory as Assistant Professor.

2011. 04. 01

Assist. Prof. Shinichi Watanabe was promoted to Associate Professor at Department of Physics, Faculty of Science and Technology, Keio University.

2011. 03. 04

Paper: "Cooling dynamics of photoexcited carriers in Si studied using optical pump and terahertz probe spectroscopy " has been published in Physical Review B.
[Phys. Rev. B 83, 085207 (2011).]

2011. 01. 14

Paper: "Intense terahertz pulse induced exciton generation in carbon nanotubes" has been published in Optics Express.
[Optics Express 19, 1528 (2011).]

2010. 07. 27

Paper: "Room temperature terahertz electro-optic modulation by excitons in carbon nanotubes" has been published in Applied Physics Letters.
[Appl. Phys. Lett. 97, 041111 (2010).]

2010. 06. 23

Paper : "Optical Hall Effect in the Integer Quantum Hall Regime" has been published in Physical Review Letters.
[Phys. Rev. Lett. 104, 256802 (2010).]

2010. 03. 24

Takeshi Suzuki received Research Incentive Award (Master Course), Graduate School of Science, The University of Tokyo.