Thermodynamic properties of the Shastry-Sutherland model from quantum Monte Carlo simulations

TL;DR

This paper demonstrates that quantum Monte Carlo simulations of the frustrated Shastry-Sutherland model can be significantly improved by exploiting a basis transformation, enabling accurate thermodynamic property calculations at low temperatures.

Contribution

The study introduces a basis formulation that reduces the sign problem in QMC for the Shastry-Sutherland model, allowing precise thermodynamic analysis across a range of couplings.

Findings

Sign problem becomes negligible at low temperatures for certain coupling ratios.

QMC results agree with tensor-network and exact diagonalization data.

Thermodynamic properties are accurately computed up to a coupling ratio of 0.526.

Abstract

We investigate the minus-sign problem that afflicts quantum Monte Carlo (QMC) simulations of frustrated quantum spin systems, focusing on spin S=1/2, two spatial dimensions, and the extended Shastry-Sutherland model. We show that formulating the Hamiltonian in the diagonal dimer basis leads to a sign problem that becomes negligible at low temperatures for small and intermediate values of the ratio of the inter- and intradimer couplings. This is a consequence of the fact that the product state of dimer singlets is the exact ground state both of the extended Shastry-Sutherland model and of a corresponding "sign-problem-free" model, obtained by changing the signs of all positive off-diagonal matrix elements in the dimer basis. By exploiting this insight, we map the sign problem throughout the extended parameter space from the Shastry-Sutherland to the fully frustrated bilayer model and compare it with the phase diagram computed by tensor-network methods. We use QMC to compute with high accuracy the temperature dependence of the magnetic specific heat and susceptibility of the Shastry-Sutherland model for large systems up to a coupling ratio of 0.526(1) and down to zero temperature. For larger coupling ratios, our QMC results assist us in benchmarking the evolution of the thermodynamic properties by systematic comparison with exact diagonalization calculations and interpolated high-temperature series expansions.