Piezoreflectance of TlCl and TlBr at Liquid Helium Temperature

Abstract

Piezo-modulated reflection spectra of the first exciton band of TlCl and TlBr are investigated at liquid helium temperature. Both the energy shift and the change in oscillator strength caused by [001] stress are observed for each component of the doublet structure in the first peak. Stress response is analysed in terms of intra- and intervalley interactions of excitons at inequivalent X points in the Brillouin zone. Diagonal term E₃−E₁ and off-diagonal term M_iv in the Hamiltonian of the intra- and intervalley interactions are estimated. Tetragonal deformation potential constant D₁³ is also obtained. Results are E₃−E₁=1.9±0.3 meV, M_iv=0.9±0.2 meV and D₁³=1.6±0.3 eV for TlCl and E₃−E₁=1.3±0.4 meV, M_iv=0.2±0.5 meV and D₁³=0.4±0.2 eV for TlBr.