Induced unconventional superconductivity on the surface states of Bi$_2$Te$_3$ topological insulator

TL;DR

This study demonstrates that superconductivity induced on Bi₂Te₃ topological insulator surface states is unconventional, exhibiting a sign-changing order parameter consistent with chiral p-wave symmetry, revealed through phase-sensitive quantum interference measurements.

Contribution

The paper provides the first phase-sensitive evidence of unconventional, sign-changing superconductivity on topological insulator surface states using nanoscale Josephson junctions.

Findings

Superconductivity on Bi₂Te₃ surface states is unconventional with a chiral p-wave component.

Magnetic field patterns show signatures of 0 and π coupling, indicating a non-trivial order parameter phase.

Thermal strain and nano-texture are key factors enabling the unconventional order parameter.

Abstract

Topological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral $p_x$ + i$p_y$ wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using Bi$_2$Te$_3$ topological insulator. We demonstrate that the induced superconductivity is unconventional and consistent with a sign-changing order parameter, such as a chiral $p_x$ + i$p_y$ component. The magnetic field pattern of the junctions shows a dip at zero externally applied magnetic field, which is an incontrovertible signature of the simultaneous existence of 0 and $\pi$ coupling within the junction, inherent to a non trivial order parameter phase. The nano-textured morphology of the Bi$_2$Te$_3$ flakes, and the dramatic role played by thermal strain are the surprising key factors for the display of an unconventional induced order parameter.