Topological surface states of Dirac fermions in $n$-Bi$_{2}$Te$_{3-y}$Se$_{y}$ thermoelectrics

In $n$-Bi$_2$Te$_3$ and $n$-Bi$_{2}$Te$_{3-y}$Se$_{y}$ thermoelectrics, the surface states of Dirac fermions of the interlayer Van der Waals surface (0001) are studied by scanning tunneling microscopy and spectroscopy. The surface morphology and modulated line profiles of the tunneling microscopy images are determined by local distortions of the surface density of electronic states and depend on the composition. The Dirac point $E_{\mathrm{D}}$ in the studied compositions is localized in the band gap and shifts to the top of the valence band with increasing Se content in $n$-Bi$_{2}$Te$_{3-y}$Se$_{y}$ alloys. The dependence between the parameters of the surface states of Dirac fermions (Dirac-point position, Fermi velocity, surface fermion concentration) and thermoelectric properties (Seebeck coefficient and power parameter) in the thermoelectrics under study is determined.