Plaquette Singlet Transition, Magnetic Barocaloric Effect, and Spin Supersolidity in the Shastry-Sutherland Model

Abstract

Inspired by recent experimental measurements on frustrated quantum magnet SrCu\(_2\)(BO\(_3\))\(_2\) under combined pressure and magnetic fields, we study the related spin-1/2 Shastry-Sutherland (SS) model using state-of-the-art tensor network methods. We find amazingly that, in zero magnetic field, there appears not only a line of first-order plaquette-singlet (PS)/plaquette liquid to dimer-singlet phase transition and its critical point, but also a second-order line with its critical endpoint terminating on this first-order line. By calculating thermodynamics, correlations and susceptibilities, we draw the finite-temperature phase diagram for the SS model, that well explains two recent experiments [Guo \(\textit{et al}\)., Phys. Rev. Lett. \(\textbf{124}\), 206602 (2020); Jim\'enez \(\textit{et al}\)., Nature \(\textbf{592}\), 370 (2021)]. Beyond the critical point, we uncover prominent magnetic barocaloric responses, a novel type of quantum correlation induced cooling effect in the strongly fluctuating supercritical regime. Under finite fields, we identify a quantum phase transition from the PS phase to the spin supersolid phase that breaks simultaneously lattice translational and spin rotational symmetries. The present findings on the SS model are accessible in current experiments and would shed new light on exotic critical and supercritical phenomena in the archetypal frustrated quantum magnets such as SrCu\(_2\)(BO\(_3\))\(_2\).