Valence Bond Glass and Glassy Spin Liquid in Disordered Frustrated Magnets

TL;DR

This paper demonstrates that disordered frustrated magnets can exhibit valence-bond glass and glassy spin liquid states, with characteristic thermodynamic signatures explained by a semiclassical Monte Carlo approach.

Contribution

It introduces a new interpretation of disordered spin-liquid behavior as valence-bond glass and glassy spin liquid states using a semiclassical Monte Carlo method.

Findings

Valence-bond glass melts into a glassy spin liquid at finite temperatures.

Low-temperature specific heat anomaly is due to collective singlet excitations.

The thermodynamic signatures are insensitive to external magnetic fields.

Abstract

The absence of conventional magnetic order together with anomalous low-temperature magnetic heat capacity is often interpreted as evidence for quantum spin liquid ground states in frustrated magnets. Using a recently developed semiclassical Monte Carlo approach, we show that similar thermodynamic signatures arise in the highly frustrated regime of the disordered spin-1/2 J1-J2 Heisenberg model on the square lattice. By analyzing the freezing parameters, the distribution of spin-spin correlations, and the specific heat, we identify the ground state as a valence-bond glass that melts into a glassy spin liquid at finite temperatures. We show that the low-temperature specific-heat anomaly originates from collective singlet excitations, and consequently it is insensitive to external magnetic fields. This leads to a robust experimental signature of the valence bond glass phase and a completely new interpretation of the thermodynamic data on disordered spin-liquid candidate materials.