Fermi-Level Pinning, Charge Transfer, and Relaxation of Spin-Momentum Locking at Metal Contacts to Topological Insulators

TL;DR

This study uses large-scale ab initio calculations to analyze how different metal contacts affect charge transfer, band bending, and spin-momentum locking in topological insulators, revealing the importance of contact metal selection.

Contribution

It provides detailed insights into the electronic interactions at metal-topological insulator interfaces, highlighting the effects of various metals on charge injection and spin properties.

Findings

Fermi level is in the conduction band for all metals studied.

No Schottky barrier exists for charge injection in the first quintuplets.

Au and graphene preserve spin-momentum locking, while Ni, Pd, and Pt relax it.

Abstract

Topological insulators are of interest for many applications in electronics and optoelectronics, but harnessing their unique properties requires detailed understanding and control of charge injection at electrical contacts. Here we present large-scale ab initio calculations of the electronic properties of Au, Ni, Pt, Pd, and graphene contacts to Bi2Se3. We show that regardless of the metal, the Fermi level is located in the conduction band, leading to n-type Ohmic contact to the first quintuplet. Furthermore, we find strong charge transfer and band-bending in the first few quintuplets, with no Schottky barrier for charge injection even when the topoplogical insulator is undoped. Our calculations indicate that Au and graphene leave the spin-momentum locking mostly unaltered, but on the other hand, Ni, Pd, and Pt strongly hybridize with Bi2Se3 and relax spin-momentum locking. Our results indicate that judicious choice of the contact metal is essential to reveal the unique surface features of topological insulators.