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

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.

slightly extended published version; 6 pages, 5 figures