Large linear magnetoresistance and evidence of degeneracy lifting of valence bands in rhombohedral phase of topological crystalline insulator SnTe
We report a comprehensive magneto-transport study on single crystalline p-type topological crystalline insulator (TCI) SnTe, across the cubic-to-rhombohedral (R3m) transition which occurs as a function of temperature. The electrical resistivity of a well-characterized SnTe crystal shows evidence for the cubic-to-rhombohedral structural transition at T$_s$ $\sim$64,K and a carrier density of $\sim$1.8$\times$10$^{20}$ at 77,K. As a function of applied magnetic field perpendicular to the (100) plane, SnTe exhibits a large unsaturated linear magnetoresistance (LMR) reaching a value of 42% at 5K and 8T. LMR is found to have a direct dependence on the mobility and a detailed analysis shows that it follows the classical Parish-Littlewood model of conductivity fluctuations arising from macroscopic inhomogeneity of tellurium interstitial atoms. We also observe SdH oscillations in the rhombohedral (R3m) phase with a Berry phase of $\pi$ and significantly lower carrier density $\sim$5.32$\times$10$^{11}$cm$^{-2}$ at 2K, which provides direct evidence of protected topological surface states in the (R3m) phase. The Hall conductivity shows a transformation from one band to two-band behavior across the structural transition, thus providing experimental evidence for the degeneracy lifting of bulk valence bands below the cubic symmetry breaking point which is consistent with recent band structure calculations. The overall results indicate that magneto-transport studies can distinctly probe the surface and bulk sensitive properties of SnTe, and can also track the band-splitting of degenerate bands at the Fermi level across the cubic-to-rhombohedral (R3m) transition.