Modulated Piezoreflectance in Bismuth

Piezoreflectance has been measured in single crystals of bismuth with light polarized in the basal plane of the crystal for photon energies in the range 0.6 to 4.5 eV. The stress modulation of the optical reflectance was achieved by cementing a nearly circular disk of bismuth onto a lead-zirconate-titanate disk set into radial oscillations at 22 kcps. Using the Kramers-Kronig analysis, the induced changes in the imaginary part of the basal component of the dielectric tensor ${\epsilon }_{\mathrm{i}j}$ have been computed from the piezoreflectance data. The energy dependence of the piezoreflectance ${(\frac{\Delta R}{R)}}_{11}$, as well as the computed changes in the dielectric constant $\Delta {\epsilon }_{11}^{\prime \prime }$, show an enhancement of the structure observed earlier by Cardona and Greenaway in the reflectivity spectrum. An assignment of the optical structure to direct interband transitions has been possible with the help of a comparison of the data with Golin's band-structure calculations.