Colloquium

Upcoming Colloquium

Unravelling the hidden state of a kagome magnet
Dr. Yona Soh, Paul Scherrer Institute, Villigen, Switzerland

September 14, 2026
11:00am-12:00pm in HSCI-102

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Abstract

Kagome lattices have been a subject of intense studies due to the geometric frustration that can give rise to exotic phases of matter such as quantum spin liquid and emergent phases that arise from flat bands. Shandite Co₃Sn₂S₂ has Co forming a kagome lattice and it has been considered a ferromagnet with c-axis as its easy axis. However, there are many controversial reports regarding its magnetism including the presence of spin glass, antiferromagnetism coexisting with ferromagnetism, and a magnetic Hamiltonian where the nearest neighbour interaction is negligible. In order to unravel the magnetism of Co₃Sn₂S₂, we have used a variety of experimental techniques, including magnetic imaging, spatially resolved Angular Resolved Photoemission Spectroscopy (ARPES), and neutron scattering. We have comprehensively solved the magnetic Hamiltonian, which is dominated by one in-plane nearest-neighbor interaction J, containing a Heisenberg component and a giant antisymmetric Dzyaloshinskii-Moriya Interaction (DMI), which is roughly 1/3 of J, and a small interplanar coupling. This giant DMI value is the largest reported in any system and causes the spins to cant and form an umbrella structure. This umbrella structure holds the key for the unusual magnetic behavior in the system and explains the giant anomalous Hall effect and chiral phonons in Co₃Sn₂S₂.