Inducing a Lifshitz Transition by Extrinsic Doping of Surface Bands in the Topological Crystalline Insulator Pb1-xSnxSe

The narrow gap semiconductor Pb1-xSnxSe was investigated for topologically protected surface states in its rocksalt structural phase for x = 0.45, 0.23, 0.15, and 0. Angle-resolved photoelectron spectroscopy of intrinsically p-doped samples showed a clear indication of two Dirac cones, eccentric about the time-reversal invariant point (X) over bar of the surface Brillouin zone for all but the x = 0 sample. Adsorption of alkalies gradually filled the surface bands with electrons, driving the x > 0 topological crystalline insulator systems through Lifshitz transitions, and from a holelike to electronlike Fermi surface. The electron-doped bands in x > 0 samples exhibited the full configuration of the Dirac cones, also confirming electron-hole symmetry of the surface bands.