# Signatures of a Deconfined Phase Transition on the Shastry-Sutherland Lattice: Applications to Quantum Critical SrCu$_2$(BO$_3$)$_2$

## TL;DR

This paper investigates a deconfined quantum phase transition in a Shastry-Sutherland lattice model, providing numerical and theoretical evidence for an emergent O(4) symmetry and predicting experimental signatures in SrCu$_2$(BO$_3$)$_2$.

## Contribution

It demonstrates the existence of a deconfined quantum critical point with emergent O(4) symmetry in a realistic lattice model, supported by iDMRG analysis and correlation spectrum analysis.

## Key findings

- Evidence for a deconfined quantum critical point (DQCP) between N{\'e}el and pVBS phases.
- Identification of emergent O(4) symmetry at the transition.
- Predicted sharp signatures of DQCP in phonon and magnon spectra.

## 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.