Quantum phases of SrCu₂(BO₃)₂ from high-pressure thermodynamics
Guo, Jing; Sun, Guangyu; Zhao, Bowen; Wang, Ling; Hong, Wenshan; Sidorov, Vladimir A.; Ma, Nvsen; Wu, Qi; Li, Shiliang; Meng, Zi Yang; Sandvik, Anders W.; Sun, Liling
We report heat capacity measurements of SrCu₂(BO₃)₂ under high pressure along with simulations of relevant quantum spin models and map out the (P,T) phase diagram of the material. We find a first-order quantum phase transition between the low-pressure quantum dimer paramagnet and a phase with signatures of a plaquette-singlet state below T=2 K. At higher pressures, we observe a transition into a previously unknown antiferromagnetic state below 4 K. Our findings can be explained within the two-dimensional Shastry-Sutherland quantum spin model supplemented by weak interlayer couplings. The possibility to tune SrCu₂(BO₃)₂ between the plaquette-singlet and antiferromagnetic states opens opportunities for experimental tests of quantum field theories and lattice models involving fractionalized excitations, emergent symmetries, and gauge fluctuations.
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