We investigated the negative photoconductivity (NPC) effect that was observed in a p-type Pb1-xSnxTe film for temperatures varying from 300 K down to 85 K. We found that this effect is a consequence of defect states located in the bandgap which act as trapping levels, changing the relation between generation and recombination rates. Theoretical calculations predict contributions to the NPC from both conduction and valence bands, which are in accordance with the experimental observations.
We report on high-field (up to 30 T) magnetotransport experiments in topological crystalline insulator (111) SnTe epitaxial films. The longitudinal magnetoresistance R xx exhibits pronounced Shubnikov-de Haas (SdH) oscillation at 4.2 K that persists up to 80 K. The second derivative (−d 2 R xx /dB 2 ) versus 1/B curve shows a clear beating pattern and the fast Fourier-transform analysis reveals that the SdH oscillations are composed of two close frequencies. As SnTe has elongated bulk Fermi ellipsoids, the 1/ cos θ dependence obtained in the angular evolution of both SdH frequencies is not sufficient to assure conduction via surface states. The Lifshitz-Kosevich fitting of the R xx oscillatory component confirms the two frequencies and enables us to extract the Berry phase of the charge carriers. The most likely scenario obtained from our analysis is that the beating pattern of these quantum oscillations originates from the Rashba splitting of the bulk longitudinal ellipsoid in SnTe.
The spin-orbit coupling is studied experimentally in two PbTe quantum wells by means of weak antilocalization effect. Using the Hikami-Larkin-Nagaoka model through a computational global optimization procedure, we extracted the spin-orbit and inelastic scattering times and estimated the strength of the zero field spin-splitting energy Δso. The values of Δso are linearly dependent on the Fermi wave vector (kF) confirming theoretical predictions of the existence of large spin-orbit coupling in IV-VI quantum wells originated from pure Rashba effect.
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