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

Inspired by recent experimental measurements [Guo et al., Phys. Rev. Lett. 124, 206602 (2020); Jim\'enez et al., Nature (London) 592, 370 (2021)] on frustrated quantum magnet ${\text{SrCu}}_{2}({\mathrm{BO}}_{3}{)}_{2}$ under combined pressure and magnetic fields, we study the related spin-$1/2$ Shastry-Sutherland model using state-of-the-art tensor network methods. By calculating thermodynamics, correlations, and susceptibilities, we find, in zero magnetic field, not only a line of first-order dimer-singlet to plaquette-singlet phase transition ending with a critical point, but also signatures of the ordered plaquette-singlet transition with its critical end point terminating on this first-order line. Moreover, 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 plaquette-singlet phase to the spin supersolid phase that breaks simultaneously lattice translational and spin rotational symmetries. The present findings on the Shastry-Sutherland model are accessible in current experiments and would shed new light on the critical and supercritical phenomena in the archetypal frustrated quantum magnet ${\text{SrCu}}_{2}({\mathrm{BO}}_{3}{)}_{2}$.