Evolution of surface states in Bi1-xSbx alloys across the topological phase transition.

We performed a systematic, high-resolution, angle-resolved photoemission spectroscopy of Bi1-xSbx alloys to study the evolution of electronic states as a function of Sb concentration x. We revealed that the number of Fermi-level crossings is different between the topologically trivial (x= 0.023) and nontrivial (x= 0.17) phases: four and five times for the former and latter cases, respectively. We also found a systematic expansion of the bandwidth of spin-split surface bands at the Γ point upon substituting Bi with Sb, which is indicative of the monotonous reduction of the spin-orbit coupling strength. [ABSTRACT FROM AUTHOR]