Non-perturbative approach to quantum liquid ground states on geometrically frustrated Heisenberg antiferromagnets

TL;DR

This paper extends topological theorems to frustrated quantum spin systems, predicting gapped quantum liquid ground states and fractional magnetization plateaux in kagome and triangular lattices.

Contribution

It introduces a twist operator approach tailored for frustrated lattices, providing new criteria for ground state degeneracy and fractionalized excitations.

Findings

Predicts a two-fold degenerate ground state with a gap in kagome antiferromagnets.

Identifies fractional magnetization plateaux at specific values.

Broad agreement with numerical and experimental results.

Abstract

We have formulated a twist operator argument for the geometrically frustrated quantum spin systems on the kagome and triangular lattices, thereby extending the application of the Lieb-Schultz-Mattis (LSM) and Oshikawa-Yamanaka-Affleck (OYA) theorems to these systems. The equivalent large gauge transformation for the geometrically frustrated lattice differs from that for non-frustrated systems due to the existence of multiple sublattices in the unit cell and non-orthogonal basis vectors. Our study for the $S=1/2$ kagome Heisenberg antiferromagnet at zero external magnetic field gives a criterion for the existence of a two-fold degenerate ground state with a finite excitation gap and fractionalized excitations. At finite field, we predict various plateaux at fractional magnetisation, in analogy with integer and fractional quantum Hall states of the primary sequence. These plateaux correspond to gapped quantum liquid ground states with a fixed number of singlets and spinons in the unit cell. A similar analysis for the triangular lattice predicts a single fractional magnetization plateau at $1/3$. Our results are in broad agreement with numerical and experimental studies.