[Seminar] Dr. Ryutaro Okuma. "Itinerant frustration in van der Waals coupled iodides"


Tuesday, August 2, 2022 - 16:30 to 17:30





Dr. Ryutaro Okuma / University of Oxford
I had been working on synthesis of novel frustrated magnets during my PhD in Prof. Zenji Hiroi’s group in the University of Tokyo. As a postdoc, I joined in Prof. Yoshinori Okada’s group in OIST. Currently I work with Prof. Radu Coldea in the University of Oxford and study spin-orbital-entangled magnets by means of neutron scattering.


Itinerant frustration in van der Waals coupled iodides


I will introduce reduced rare earth iodides as a novel type of van der Waals (vdW) coupled materials that displays nontrivial magnetism due to itinerant frustration.
(1) CeSiI consists of conductive honeycomb net of Si2- with a bilayer triangular lattice of Ce3+ and a vdW stacking of I-. By neutron diffraction, we have found a cycloidal magnetic order coexisting with Fermi surface that a magnetic field can transform to a nontrivial magnetic structure [1].
(2) GdGaI is isostructural to CeSiI but a semiconductor with an indirect band gap of 0.1 eV at ambient temperature. Our angle-resolved photoemission spectroscopy measurements revealed a band folding with q = (1/2, 0) at low temperatures. Appearance of a tiny ferromagnet moment indicates formation of the smallest Skyrmion crystal by triplet exciton condensation.
[1] R. Okuma, C. Ritter, G. J. Nilsen, & Y. Okada Phys. Rev. Mater. 5, L121401(2021).


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