Quantum Phases and Phase Transitions in Designer Spin Models
by Dr. Nisheeta Desai (University of Kentucky)
Thursday, November 26, 2020 from to (Asia/Kolkata)
We introduce a procedure to write down lattice models with spin-rotation invariant Hamiltonians for arbitrary spin-S, which can be simulated efficiently without a sign problem in Quantum Monte Carlo studies. As the first application of our approach, we design a square lattice S = 1 model that realizes a novel “Haldane nematic” phase. This phase breaks lattice rotational symmetry by the spontaneous formation of Haldane chains, while preserving spin rotations, time reversal and lattice translations. By supplementing our model with a two-spin Heisenberg interaction, we present a study of the transition between N\'eel and Haldane nematic phases, which we find to be of first order. As another application of our procedure, we study the N\'eel to four-fold columnar valence bond solid (cVBS) quantum phase transition in a sign free S=1 square lattice model. Extensive numerical simulations of the square lattice S=1/2 N\'eel-VBS transition have found consistency with the DCP scenario with no direct evidence for first order behavior. In contrast to the S=1/2 case, in our quantum Monte Carlo simulations for the S=1 model, we present unambiguous evidence for a direct conventional first-order quantum phase transition.