Abstract
We study a possible deconfined quantum phase transition in a realistic model of a two-dimensional Shastry-Sutherland quantum magnet, using both numerical and field theoretic techniques. Using the infinite density matrix renormalization group (iDMRG) method, we verify the existence of an intermediate plaquette valence bond solid (pVBS) order, with two fold degeneracy, between the dimer and N\'eel ordered phases. We argue that the quantum phase transition between the N\'eel and pVBS orders may be described by a deconfined quantum critical point (DQCP) with an emergent O(4) symmetry. By analyzing the correlation length spectrum obtained from iDMRG, we provide evidence for the DQCP and emergent O(4) symmetry in the lattice model. Such a phase transition has been reported in the recent pressure tuned experiments in the Shastry-Sutherland lattice material $\mathrm{SrCu_2 (BO_3)_2}$. The non-symmorphic lattice structure of the Shastry-Sutherland compound leads to extinction points in the scattering, where we predict sharp signatures of a DQCP in both the phonon and magnon spectra associated with the spinon continuum. The effect of weak interlayer couplings present in the three dimensional material is also discussed. Our results should help guide the experimental study of DQCP in quantum magnets.
Highlights
Quantum magnets can host some of the most exotic phenomena in condensed matter physics, due to the strong quantum fluctuations of the microscopic spin degrees of freedom (d.o.f.)
Such behavior can exist either in a quantum spin liquid, which is a stable phase of matter with topological order [1,2,3], or by tuning a single parameter to a critical point known as the deconfined quantum critical point (DQCP) [4,5]
The goal of this work is to investigate the plaquette valence bond solid (PVBS)-Neel transition in the Shastry-Sutherland model Eq (1) in more detail using both the field theory and the density matrix renormalization group (DMRG) approach and to identify the unique signatures of a DQCP that can be probed by inelastic neutron scattering (INS) or resonant inelastic x-ray scattering (RIXS) experiments
Summary
Quantum magnets can host some of the most exotic phenomena in condensed matter physics, due to the strong quantum fluctuations of the microscopic spin degrees of freedom (d.o.f.). Since the PVBS and Neel phases separately break two distinct symmetries, the lattice and the spin-rotation symmetry, a direct second-order transition between them would necessarily go beyond the Landau-Ginzburg paradigm and point to the possibility of the DQCP. The goal of this work is to investigate the PVBS-Neel transition in the Shastry-Sutherland model Eq (1) in more detail using both the field theory and the density matrix renormalization group (DMRG) approach and to identify the unique signatures of a DQCP that can be probed by inelastic neutron scattering (INS) or resonant inelastic x-ray scattering (RIXS) experiments.
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