Short-range magnetic interactions and optical band-edge physics inSrCu2(BO3)2

Abstract

Optical reflectivity spectra of ${\mathrm{SrCu}}_{2}$$({\mathrm{BO}}_{3})$${}_{2}$ revealed a feature at 1.5 eV assigned as the energy gap for the charge-transfer excitation. Changes in the optical reflectivity induced by temperature and applied magnetic field were compared to population statistics to establish a correlation between the optical changes and magnetic excitations on the dimers. A Curie-like analysis of the optical data demonstrated that the Weiss constant and spin-gap energy obtained from an analysis of the magnetic susceptibility could also be used to describe reflectivity changes at the band edge. Differences between the temperature- and magnetic field-induced changes to the optical data were also identified and interpreted as potentially indicative of a multitriplet or cooperative interaction between dimer spin excitations and band-edge charge carriers.