Thermally populated versus field-induced triplon bound states in the Shastry-Sutherland lattice SrCu$_2$(BO$_3$)$_2$

TL;DR

This study uses high-field Raman spectroscopy to explore how magnetic field and temperature influence bound states of triplons in the Shastry-Sutherland lattice SrCu$_2$(BO$_3$)$_2$, revealing their similar and distinct effects on these quasiparticles.

Contribution

It provides new insights into the field and temperature dependence of triplon bound states and their correlated dynamics in a frustrated quantum magnet.

Findings

Magnetic field and temperature similarly melt singlet bound states.

Spectral shapes are affected differently by field and temperature.

Anti-crossing of singlet bound states observed in intermediate fields.

Abstract

The Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$ constituting orthogonally coupled dimers harbors a $S=0$ singlet ground state. The confluence of strong interdimer interaction and frustration engenders a spectrum of low-energy excitations including localized triplons as well as singlet and triplet bound states. Their dynamics are controlled by an external magnetic field and temperature. Here, we employ high-field Raman spectroscopy to map the field and temperature evolution of such bosonic composite quasiparticles on approaching the 1/8 magnetization plateau. Our study unveils that the magnetic field and thermal fluctuations show remarkably similar effects in melting the singlet bound states, but are disparate in their effects on the fine spectral shapes. This, together with the anti-crossing of two singlet bound states in the intermediate field $B=10-16$ T, is discussed in terms of the correlated dynamics of frustrated, interacting bosons.