Temperature-driven band inversion in Pb$_{0.77}$Sn$_{0.23}$Se: Optical   and Hall-effect studies
  Optical and Hall-effect measurements have been performed on single crystals of Pb$_{0.77}$Sn$_{0.23}$Se, a IV-VI mixed chalcogenide. The temperature dependent (10--300 K) reflectance was measured over 40--7000 cm$^{-1}$ (5--870 meV) with an extension to 15,500 cm$^{-1}$ (1.92 eV) at room temperature. The reflectance was fit to the Drude-Lorentz model using a single Drude component and several Lorentz oscillators. The optical properties at the measured temperatures were estimated via Kramers-Kronig analysis as well as by the Drude-Lorentz fit. The carriers were p-type with the carrier density determined by Hall measurements. A signature of valence intraband transition is found in the low-energy optical spectra. It is found that the valence-conduction band transition energy as well as the free carrier effective mass reach minimum values at 100 K, suggesting temperature-driven band inversion in the material. Density function theory calculation for the electronic band structure also make similar predictions. 
Naween Anand (1), Zhiguo Chen (2), Sanal Buvaev (1), Kamal Choudhary   (3), C. Martin (5), Genda Gu (4), S. B. Sinnott (3), ...
cond-mat.str-el cond-mat.mes-hall