Spin-orbital groundstates of Superconducting doped topological insulators (A Majorana Platform)

TL;DR

This study investigates the spin-orbital groundstates of superconducting doped topological insulators, revealing persistent topological surface states and their potential to host Majorana fermions, with implications for topological quantum computing.

Contribution

It provides detailed experimental analysis of the spin-orbital states in doped topological insulators and explores their superconducting and topological properties, highlighting the potential for Majorana modes.

Findings

Topological surface states remain well-defined in superconducting doped Bi2Se3.

Majorana zero modes are expected at superconducting vortices on the surface.

Surface electronic modes show renormalization and charge correlation instabilities.

Abstract

The Bi$_2$Se$_3$ class of topological insulators has recently been shown to undergo a superconducting transition upon hole or electron doping (Cu$_x$-Bi$_2$Se$_3$ with T$_C$=3.8$^o$K and Pd$_x$-Bi$_2$Te$_3$ with T$_C$=5$^o$K), raising the possibilities that these are the first known "topological superconductors" or realizes a superconducting state that can be potentially used as Majorana platforms (L.A. Wray \textit{et.al.}, Nature Phys. \textbf{6}, 855-859 (2010)). We use angle resolved photoemission spectroscopy to examine the full details of the spin-orbital groundstates of these materials including Bi$_2$Te$_3$, observing that the spin-momentum locked topological surface states remain well defined and non-degenerate with respect to bulk electronic states at the Fermi level in the optimally doped superconductor and obtaining their experimental Fermi energies. The implications of this unconventional surface (that undergoes superconducting at lower temperatures) topology are discussed, and we also explore the possibility of realizing the same topology in superconducting variants of Bi$_2$Te$_3$ (with T$_C$ $\sim$ 5$^o$K). Characteristics of the experimentally measured three dimensional bulk states are examined in detail for these materials with respect to the superconducting state and topological properties, showing that a single Majorana fermion zero mode is expected to be bound at each superconducting vortex on the surface. Systematic measurements also reveal intriguing renormalization and charge correlation instabilities of the surface-localized electronic modes.