Anomalous thermoelectric power and polaronic transport in the vicinity of topological phase transition of Pb1-xSnxTe

Abstract Pb 1− x Sn x Te compounds exhibits the topological phase transition from trivial semiconductor (PbTe) to topological crystalline insulator (SnTe). In the vicinity of topological phase transition in the region of Pb 1− x Sn x Te ( x = 0.2, 0.3, and 0.4), the band touching of conduction L 6 − and valence L 6 + bands gives rise to topological Dirac semimetal. Here we investigated thermoelectric properties in the region of topological Dirac semimetal in Pb 1− x Sn x Te compounds. From the temperature-dependent Hall R H ( T ) and Seebeck coefficients S ( T ) , we found the abnormal sign difference between Hall (positive R H ) and Seebeck (negative S ) coefficients in the compounds of x = 0.3 and x = 0.4 at intermediate temperature range. We analyzed the abnormal sign difference between the Hall and Seebeck coefficients in terms of the Aharanov-Bohm effect of non-adiabatic 3-site polaron hopping. The polaronic hopping in the compounds can be justified by strong electron-phonon coupling. The temperature-dependent behavior of Hall mobility μ H ( T ) and carrier density n H ( T ) indicates the strong electron-phonon scattering. From the temperature-dependent thermal conductivity κ ( T ) measurement, the broad peaks at low temperature, driven by freezing-out of Umklapp scattering, are systematically suppressed by increasing Sn concentration, which consistent with the strong electron-phonon interaction in the system.