Evidence for a $\mathbb{Z}_{2}$ Dirac spin liquid in the generalized Shastry-Sutherland model

TL;DR

This paper provides comprehensive evidence for a $ ext{Z}_2$ Dirac spin liquid phase in the Shastry-Sutherland model, combining multiple computational methods and theoretical classifications to identify its properties and experimental signatures.

Contribution

It identifies a $ ext{Z}_2$ Dirac spin liquid in the Shastry-Sutherland model, linking it to known phases on the square lattice and providing detailed computational and theoretical analysis.

Findings

Identification of a $ ext{Z}_2$ Dirac spin liquid phase.

Agreement between variational Monte Carlo, neural quantum states, and DMRG results.

Spectral features consistent with Dirac cones in excitation spectrum.

Abstract

We present a multimethod investigation into the nature of the recently reported quantum spin liquid (QSL) phase in the spin-$1/2$ Heisenberg antiferromagnet on the Shastry-Sutherland lattice. A comprehensive projective symmetry group classification of fermionic mean-field Ans\"atze on this lattice yields 46 U(1) and 80 $\mathbb{Z}_2$ states. Using density-matrix renormalization group (DMRG) and exact diagonalization calculations, we find that the Shastry-Sutherland model and the square-lattice $J_1$-$J_2$ Heisenberg antiferromagnet share the same QSL phase. Motivated by this observation, we establish an explicit mapping of our Ans\"atze to those on the square lattice, and identify the counterpart of the square-lattice $\mathbb{Z}_2$ Dirac QSL (Z2A$zz$13) in the Shastry-Sutherland system. Employing state-of-the-art variational Monte Carlo calculations with Gutzwiller-projected wavefunctions, further improved by L\'anczos steps, we demonstrate excellent agreement in both energies and correlation functions between a gapless (Dirac) $\mathbb{Z}_2$ spin liquid-characterized by only a few variational parameters-and results obtained from neural quantum states and DMRG. Finally, we apply the recently developed Keldysh formulation of the pseudo-fermion functional renormalization group to compute the dynamical spin structure factor. The resulting spectra exhibit features consistent with Dirac cones in the excitation spectrum, providing strong independent evidence for a Dirac QSL ground state. Our identification of a $d$-wave pairing $\mathbb{Z}_2$ Dirac QSL is consistent with recently observed signatures of QSL behavior in Pr$_2$Ga$_2$BeO$_7$ and outlines predictions for future experiments.