Theory of the Raman spectra of the Shastry-Sutherland antiferromagnet SrCu$_2$(BO$_3$)$_2$ doped with nonmagnetic impurities

TL;DR

This paper develops a theoretical framework for understanding the Raman spectra of SrCu$_2$(BO$_3$)$_2$ doped with nonmagnetic impurities, revealing bound-states below the spin gap and proposing Raman spectroscopy as a key probe.

Contribution

It introduces a new effective model and exact diagonalization approach to analyze impurity-induced bound-states and their Raman signatures in the Shastry-Sutherland antiferromagnet.

Findings

Bound-states below the spin gap are identified.

Raman spectroscopy can uniquely probe these bound-states.

Quantitative Raman spectra are numerically predicted.

Abstract

Controlled doping of SrCu$_2$(BO$_3$)$_2$, a faithful realization of the Heisenberg spin-1/2 antiferromagnet on the Shastry-Sutherland lattice, with non-magnetic impurities generates bound-states below the spin gap. These bound-states and their symmetry properties are investigated by exact diagonalisation of small clusters and within a simple effective model describing a spinon submitted to an attractive extended potential. It is shown that Raman spectroscopy is a unique technique to probe these bound-states. Quantitative theoretical Raman spectra are numerically obtained.