Easily Accessible Topologically Protected Charge Carriers in Pure and Robust alpha-Sn Films

Abstract

Experimental evidence of topological Dirac fermion charge carriers in pure and robust alpha-Sn thin films grown on InSb substrates is reported. This evidence is acquired using standard macroscopic four-point contact resistance measurements, conducted on uncapped films with a significantly reduced bulk mobility. The electrical characteristics of the constituting components of the alpha-Sn/InSb sample are analyzed and compared and a three-band drift velocity model is proposed accordingly. A surface band, with low carrier density and high mobility, is identified as the origin of the observed Shubnikov - de Haas (SdH) oscillations. The analysis of these quantum oscillations results in a nontrivial value of the phase shift gamma(0), characteristic of topologically protected Dirac fermions. The momentum relaxation time tau approximate to 300 fs in pure, undoped alpha-Sn thin films is estimated.