Far infrared conductivity and dielectric response of semiconducting SmS

Abstract

Far infrared reflectivity (30–700 cm −1) of high quality SmS single crystal was measured as a function of temperature (300–50 K). The reflectivity was evaluated by means of Kramers-Kronig analysis as well as fitted to the Drude-Lorentz model. With the same sample, also dc conductivity and Hall effect was measured and perfect agreement between dc and IR conductivity at 300 K was found. The fit at 300 K yields relaxation time τ = (5.3±0.5)10 −15s, effective mass m∗ = (0.20±0.02) m e and mean free path 1 = (14±2) A°. The low value of the effective mass prefers the s-electron rather than the d-electron nature of the conduction band. The electron plasma is heavily damped and the loss function Im ε(ν) −1 demonstrates a strong coupling between LO phonon and plasmon mode. Additional fine absorption structure is seen especially at low temperatures both below and above the TO phonon frequency of 180 cm −1.