Colloquium

Upcoming Colloquium

Nontrivial band-topology in dimerized quantum magnets
Dr. Judit Romhanyi, UC Irvine

February 24, 2025
11:00am in HSCI-105

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Understanding and distinguishing different phases of matter has been a central topic of condensed matter physics. The Landau theory of phase transitions provides a systematic route to achieve this goal based on symmetry-breaking local order parameters. However, exotic disordered phases that break no symmetries fall outside the Landau paradigm. Topologically distinct phases are characterized by non-local topological indices, and they do not require symmetry breaking but are rather enabled by the preservation of a symmetry. Quantum magnets offer an excellent playground for exploring topological phases. Besides the ground state properties, topology can bring new insights into the nature of excitations of quantum magnets. Magnetic excitations form bands similar to electrons, and the spin-orbit interaction, which is naturally present in magnetic compounds, can render these bands topologically nontrivial. As a result, magnets with trivial symmetry-breaking ground states can have nontrivial dynamical and Hall transport properties. In this talk, we consider spin-gap systems in which the ground state is a (trivial) valence bond singlet state and the triplet excitations form bands with nontrivial topology. We will discuss the triplet Chern bands formed in SrCu2(BO3)2 and the triplet nodal lines and Weyl points in XCuCl3 (X=K, Tl) detailing the role of magnetic anisotropies and external magnetic fields. Furthermore, we will investigate the realization of a triplet analog for Z2 band topology using a bilayer kagome lattice.

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