Spin waves and three-dimensionality in the high-pressure antiferromagnetic phase of SrCu$_2$(BO$_3$)$_2$

TL;DR

This study uses high-pressure inelastic neutron scattering to explore the spin wave behavior and three-dimensional magnetic interactions in SrCu$_2$(BO$_3$)$_2$, revealing pressure-induced changes in magnetic coupling and the importance of inter-layer interactions.

Contribution

It provides the first detailed characterization of spin waves in the high-pressure antiferromagnetic phase of SrCu$_2$(BO$_3$)$_2$ and demonstrates the significance of three-dimensional effects in its magnetic behavior.

Findings

Identification of spin waves in the high-pressure phase.

Determination of inter-layer interaction $J_c = 0.053(3)$ meV.

Observation of a sharp change in the ratio $J'/J$ at high pressure.

Abstract

Quantum magnetic materials can provide explicit realizations of paradigm models in quantum many-body physics. In this context, SrCu$_2$(BO$_3$)$_2$ is a faithful realization of the Shastry-Sutherland model (SSM) for ideally frustrated spin dimers, even displaying several of its quantum magnetic phases as a function of pressure. We perform inelastic neutron scattering (INS) measurements on SrCu$_2$(BO$_3$)$_2$ at 5.5 GPa and 4.5 K, observing spin waves that characterize the high-pressure antiferromagnetic phase. The experimental spectra are well described by linear spin-wave calculations on a SSM with an inter-layer interaction, which is determined accurately as $J_c = 0.053(3)$ meV. The presence of $J_c$ indicates the need to account for the three-dimensional nature of SrCu$_2$(BO$_3$)$_2$ in theoretical models, also at lower pressures. We find that the ratio between in-plane interactions, $J'/J = 1.8(2)$, undergoes a dramatic change compared to lower pressures that we deduce is driven by a sharp drop in the dimer coupling, $J$. Our results underline the wide horizons opened by high-pressure INS experiments on quantum magnetic materials.