Observation of a Tunable Isolated Dirac Point in $Ge(Bi_{x}Sb_{1-x})_{2}Te_{4}$

Novel topological devices require the isolation of topological surface states from trivial bulk states for electronic transport. In this study, we examine a tunable topological system, $Ge(Bi_{x}Sb_{1-x})_{2}Te_{4}$, for a range of x values, using a combination of Fourier Transform Scanning Tunneling Spectroscopy (FT-STS) and Angle-Resolved Photoemission Spectroscopy (ARPES). We track the evolution of the bulk and surface state band structure for different values of x from 1 to 0.4. Our results show that the system remains topologically non-trivial down to x = 0.4, extending the range predicted by previous computational studies. Importantly, we find that the Dirac point crosses the Fermi energy near x = 0.65. Our observation of a tunable Dirac point which crosses into the topological transport regime can be important for topological spintronics applications.