Virtual Quantum Cafe: Leon Balents

Quantum Café is CCQ’s ongoing seminar series: open to all bona fide members of the greater NYC scientific community and held every second week, Quantum Café presents a series of informal, highly interactive talks, typically by external speakers, which present the most interesting recent developments and open questions in our field.

Topic: Spectral Signatures of Quasiparticle Interactions in Spin Liquids and Heisenberg Chains

Abstract: Many body ground states are often characterized by their quasiparticle excitations. In insulating spin systems with conventional ordered or dimerized states, these are typically bosonic magnons or triplons, which interact weakly. Some more exotic quantum phases such as 2d quantum spin liquids or one-dimensional chains may have quasiparticles with fractional quantum numbers and often fermionic statistics. The commonly used slave particle approach for 2d spin liquids treats these quasiparticles as weakly interacting fermions, but as I will discuss, this can be qualitatively incorrect in many cases. I will argue theoretically that fermion-fermion interactions completely modify the small wavevector part of the dynamical spin correlations in the archetypal spin on Fermi surface spin liquid in a small applied magnetic field. Moreover, very similar effects of fermion-fermion interactions occur in 1d Heisenberg chains, for which a systematic comparison of theory and numerical simulation is possible. In the latter case, we also expose signatures of interactions of *bosonic* quasiparticles in high magnetic fields. This work is a collaboration with Oleg Starykh (U. Utah) and Anna Keselman (KITP).