Majorana chiral spin liquid in Mott insulating cuprates

TL;DR

This paper predicts a Majorana chiral spin liquid state in Mott insulating cuprates, explaining the large thermal Hall effect as arising from proximity to a topological quantum spin liquid phase induced by magnetic fields.

Contribution

It introduces a theoretical model for a Majorana chiral spin liquid in cuprates, highlighting conditions under which it becomes the ground state or an excited state.

Findings

Majorana chiral spin liquid has Chern number ±4.

Orbital magnetic field can stabilize the phase as ground state.

Large thermal Hall conductivity linked to proximity to this phase.

Abstract

The large thermal Hall conductivity recently detected in Mott insulating cuprates has been attributed to chiral neutral spin excitations. A quantum spin liquid with Majorana excitations, Chern number +/-4 and large thermal Hall conductivity is found to be an excited state of a frustrated Heisenberg model on the square lattice. Using a Majorana mean-field theory and exact diagonalizations, we explore two possible routes to achieve this chiral quantum spin liquid, an orbital effect of an applied magnetic field and spin orbit couplings as present in cuprates. In particular, we show how only the orbital magnetic field allows this topological phase to be the ground state, while it remains an excited state of the Majorana mean field under the Dzyaloshinskii-Moriya terms. We interpret the large thermal Hall effect observed in Mott cuprates from their close proximity to a transition to a Majorana chiral quantum spin liquid which can be induced by an external magnetic field.