APhMS Special Seminar

**Refreshments outside Noyes at 9:15am

Abstract:

Frustrated magnets, characterized by competing interactions that suppress conventional magnetic order, can host unconventional spin textures with emergent electromagnetic responses. Magnetic skyrmions, topologically nontrivial spin solitons, are often found in noncentrosymmetric materials or interfacial symmetry-broken heterostructures. However, theories predict that magnetic frustration can also stabilize skyrmions. We have experimentally demonstrated and established a design principle for centrosymmetric skyrmion-hosting materials [1]. In addition, we explore rare-earth-based layered semimetals with spin moiré superlattices, where multiple incommensurate spin modulations are superimposed to generate a periodic exchange potential, as in the crystallographic moiré superlattices due to twist or lattice mismatch. We observed the field-induced transitions to multiple-q spin moiré states accompanied by significant resistivity changes and giant Hall response in EuAg4Sb2 [2]. Electronic structure studies using ARPES, quantum oscillations, and DFT calculations reveal a quasi two-dimensional Fermi surface nested to a magnetic Brillouin zone of the spin moiré superlattice. The long mean free path of the conduction electrons, exceeding the period of the spin modulation, enables the realization of the reconstructed Fermi surfaces and the anomalous transport behavior.

Time permitting, I will talk about the recent exploration of new rare earth intermetallics that exhibit unconventional magnetic structures and anomalous magnetotransport properties [3,4].

References:

[1] T. Kurumaji, T. Nakajima, M. Hirschberger, A. Kikkawa, Y. Yamasaki, H. Sagayama, H. Nakao, Y. Taguchi, T.-h. Arima, and Y. Tokura, Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet, Science 365, 914 (2019).

[2] T. Kurumaji, N. Paul, S. Fang, P. M. Neves, M. Kang, J. S. White, T. Nakajima, D. Graf, L. Ye, M. K. Chan, T. Suzuki, J. Denlinger, C. Jozwiak, A. Bostwick, E. Rotenberg, Y. Zhao, J. W. Lynn, E. Kaxiras, Riccardo Comin, L. Fu, and J. G. Checkelsky, Electronic commensuration of a spin moiré superlattice in a layered magnetic semimetal, Science Advances 11, eadu6686 (2025).

[3] T. Kurumaji, S. Fang, L. Ye, S. Kitou, and J. G. Checkelsky, Metamagnetic multiband Hall effect in Ising antiferromagnetic ErGa2, PNAS 121, e2318411121 (2024).

[4] T. Kurumaji, M. Gen, S. Kitou, H. Sagayama, H. Nakao, and T.-h. Arima, Canted antiferromagnetism in a spin-orbit coupled Seff = 3/2 triangular-lattice magnet DyAuGe, arXiv:2401.16622 (2024), accepted at Nat. Commun. (2025).

More about the Speaker:

Dr. Takashi Kurumaji graduated with a B.S. in applied physics from the University of Tokyo (Japan) in 2010. He received his M.S. from the University of Tokyo, where he also received his Ph.D in 2014. From 2014 to 2017, Dr Kurumaji was a postdoctoral researcher at RIKEN Center for Emergent Matter Science in Japan, working with Dr. Yoshinori Tokura. From 2017 to 2020, he was working as a postdoctoral researcher with Dr. Joseph G. Checkelsky at MIT, and from 2020 to 2023 he was a research associate at University of Tokyo working with Dr. Takahisa Arima. Since September 2023, he has become a Research Professor of PMA at Caltech. Dr. Kurumaji's research is centered on the synthesis, discovery, and characterization of novel magnetic materials by using neutron and synchrotron x-ray diffraction. He has made key contribution to establishing design principle of magnetic skyrmions and multiferroics. In 2022, he was awarded the Japan Physics Society Young Scientist Award in the field of strongly correlated electron systems.