Quantum spin liquid phase in the Shastry-Sutherland model detected by an improved level spectroscopic method

TL;DR

This paper introduces an improved level spectroscopic method to accurately identify quantum critical points in the Shastry-Sutherland model, revealing a spin liquid phase between known magnetic states with high precision.

Contribution

The authors develop a novel spectroscopic technique using composite energy gaps that reduces finite-size effects, enabling precise detection of phase boundaries in quantum spin models.

Findings

Identification of a spin liquid phase between plaquette-singlet and antiferromagnetic states.

High-precision determination of phase boundaries consistent with recent DMRG results.

Method shows potential for broad application in quantum critical phenomena studies.

Abstract

We study the spin-$1/2$ two-dimensional Shastry-Sutherland spin model by exact diagonalization of clusters with periodic boundary conditions. We develop an improved level spectroscopic technique using energy gaps between states with different quantum numbers. The crossing points of some of the relative (composite) gaps have much weaker finite-size drifts than the normally used gaps defined only with respect to the ground state, thus allowing precise determination of quantum critical points even with small clusters. Our results support the picture of a spin liquid phase intervening between the well known plaquette-singlet and antiferromagnetic ground states, with phase boundaries in almost perfect agreement with a recent density matrix renormalization group study, where much larger cylindrical lattices were used [J. Yang et al., Phys. Rev. B {\bf 105}, L060409 (2022)]. The method of using composite low-energy gaps to reduce scaling corrections has potentially broad applications in numerical studies of quantum critical phenomena.