"Gauge theories of the Heisenberg antiferromagnet on kagome" Seminar by Oleg Tchernyshyov (Johns Hopkins Universit

Theory of Quantum Matter Unit would like to invite you to a seminar by Prof. Oleg Tchernyshyov (Johns Hopkins University).

• Speaker: Oleg Tchernyshyov, Associate Professor at  Department of Physics and Astronomy, The Johns Hopkins University
• Title: "Gauge theories of the Heisenberg antiferromagnet on kagome"
• Date / Time: 27th Nov (Thu) / 13:30-14:30
• Venue: C015, Lab1

Gauge theories of the Heisenberg antiferromagnet on kagome

Oleg Tchernyshyov (Johns Hopkins University)

For 25 years, the Heisenberg antiferromagnet on kagome has been a promising theoretical model of a quantum spin liquid beyon one spatial dimension. Introduced by Veit Elser in 1989 in the context of helium-3 on a graphite substrate, it has recently been realized in a distorted spinel compound herbertsmithite, where copper spins form well separated kagome layers. This compound has exchange interactions of strength J = 200 K but no long-range magnetic order even at temperatures as low as 50 mK. Inelastic neutron scattering provides strong evidence for unconventional spin excitations in the form of solitons with fractional spin 1/2. I will review our attempts to build a theory of this spin liquid. Starting with the Heisenberg model at the high-energy scale (J), we derived an effective theory valid at medium energies (a fraction of J) that has "matter" particles with spin 1/2 and Fermi statistics interacting with a compact U(1) gauge field. A phenomenology based on a Z_2 gauge field, applicable below the spin gap (roughly J/20), explains many puzzling features found in recent numerical DMRG calculations on long kagome cylinders.