Scanning tunneling spectroscopy of the surface states of Dirac fermions in thermoelectrics based on bismuth telluride

Abstract

Morphology of the interlayer van der Waals surface and differential tunneling conductance in p-Bi2-xSbxTe3-ySey solid solutions were studied by scanning tunneling microscopy and spectroscopy in dependence on compositions. Topological characteristics of the Dirac fermion surface states were determined. It is shown that the thermoelectric power factor and the material parameter enhance with the shift of the Dirac point to the top of the valence band with increasing of atomic substitution in these thermoelectrics. Correlation between topological characteristics, power factor and material parameter was found. A growth contribution of the surface states is determined by an increase of the Fermi velocity for large atomic substitutions of Bi at x>1.5 and small substitutions in the Te sublattice (y=0.06). In compositions with smaller substitutions at x = (1-1.3) and y=(0.06-0.09), similar effect of the surface states is determined by raise of the surface concentration of charge carriers.