Quantum Phase Transition between Plaquette and Neel Phases in a Quantum Magnet on the Shastry-Sutherland Lattice

A recent experiment [1] on a Shastry-Sutherland (SS) material under pressure provides us with the first evidence of a phase transition between an antiferromagnet and a 2-fold degenerate 4-spin plaquette singlet state in a material. It is also potentially the first experimental realization of the deconfined quantum critical point. However, due to the frustrated couplings in the original SS model, it is challenging to study this model using unbiased numerical approaches, especially because of sign problems in quantum Monte Carlo simulations. Therefore, the nature of the phase transition has not yet been studied in detail. Here we propose a "designer Hamiltonian" describing the same physics as that in the experimental material but without traditional frustration. We instead construct a suitable J-Q model, a Heisenberg model extended by a particular 4-spin interaction on the SS lattice. Sign-free quantum Monte Carlo calculation shows that this model indeed hosts a quantum phase transition from the Neel ground state into a plaquette singlet phases. We will discuss the nature of the transition and a possible emergent higher symmetry.
[1] M. E. Zayed et al., Nat. Phys. 108, 1069 (2017).