Breathing kagome XY quantum magnet with four-site ring exchange

TL;DR

This paper investigates how trimerization affects the phase diagram and excitations of a kagome XY quantum magnet with ring exchange, revealing a continuous quantum critical line and signatures of spinon continua.

Contribution

It provides the first quantum Monte Carlo study of the breathing kagome XY model with ring exchange, extending understanding of its quantum phase diagram and excitations.

Findings

Trimerization extends the quantum critical point into a line in parameter space.

Elementary excitations are well-described by spin wave theory in ordered phases.

Spin liquid phase shows signatures of spinon continua.

Abstract

We study the impact of trimerization (breathing) of the nearest-neighbor (NN) exchange on the planar XY spin-1/2 ferromagnet on the kagome lattice, including additional four-site ring exchange. For uniform NN exchange, this model has previously been shown to transit from a long-range ordered ferromagnet into a Z2 quantum spin liquid by virtue of the ring exchange. Using quantum Monte-Carlo calculations, based on the stochastic series expansion, we present results for the spin stiffness, the quantum phase diagram, the longitudinal static, as well as the transverse dynamic structure factor. Our results corroborate 3D XY universality also at finite trimerization and suggest a simple continuation of the quantum critical point of the uniform case into a line in terms of rescaled exchange parameters. Moreover, at any trimerization and in the ordered phase the elementary excitations can be understood very well in terms of linear spin wave theory, while beyond the critical line, in the spin liquid phase we find signatures of spinon continua.