Tunneling spectroscopy of chiral states in ultra-thin topological insulators

Abstract

The temperature, Fermi-level, and bias dependencies of the inter-surface tunneling current in thin-film topological insulators show unique, identifying signatures of the surface states and their opposite chiralities. The opposite chiralities of the surface states limit the tunneling to the band edges of the gapped Dirac cones. As a result, the tunneling conductance is sensitive to the temperature, the Fermi level, and the surface-surface potential difference. The temperature dependence of the tunneling conductance changes sign as the Fermi level scans through the Dirac point. The tunneling transmission is a minimum when the opposing surface Dirac cones are perfectly aligned in energy. This minimum state of the tunneling channel can result in negative differential resistance (NDR) in the presence of a built-in Rashba-like splitting. The unique thermal response of the tunneling conductance and the existence of NDR suggest a tunneling spectroscopy experiment to demonstrate the opposite chiralities of the opposing surface states.