Superconductivity in a misfit phase combining a topological crystalline insulator and a layered transition metal dichalcogenide

Abstract: We report the characterization of the misfit compound (Pb1-xSnxSe2)1.16(TiSe2)2, in which a [100] rocksalt bilayer of Pb1-xSnxSe, which is a topological crystalline insulator in bulk form, alternates with a double layer of the normally non-superconducting layered transition metal dichalcogenide TiSe2. The x dependence of Tc displays a weak dome-like shape with a maximum Tc of 4.5 K at x = 0.2; there is only a subtle change in Tc corresponding to the expected trivial to topological transition in the Pb1-xSnxSe bi-layer. We present a more detailed characterization of the superconductor at x = 0.4, for which the bulk Pb1-xSnxSe phase is in the topological crystalline insulator regime. For this material, the Sommerfeld parameter gamma =11.06 mJ mol-1 K-2, the Debye temperature delta D = 161 K, the normalized specific heat jump value delta C/ gamma Tc = 1.38 and the electron-phonon constant value lambda ep = 0.72, suggesting that (Pb0.6Sn0.4Se)1.16(TiSe2)2 is a BCS-type weak coupling superconductor. This material is of interest for probing the interaction of superconductivity with the surface states of a topological crystalline insulator.