Topological delocalization against Anderson localization observed in Bi-doped PbSb2Te4 disordered topological insulator

Abstract

We experimentally investigate the tendency of localization in the bulk and the topological surface states in topological insulators Pb(Bi1-xSbx)2Te4 (x=0.793-0.818) through detailed transport measurements. The bulk electronic states in the range 0.793<=x<0.818 are situated on the insulator side of the Anderson transition, as indicated by k_Fl values (where k_F is the Fermi wavenumber and l is the mean free path) falling below the Ioffe-Regel criterion (i.e., k_F l<1). In contrast, the topological surface states retain high mobility and even exhibit quantum oscillations, demonstrating their resilient nature against strong disorder. These findings highlight the delocalized nature of the topological surface states despite Anderson localization of the bulk electronic states.