The Coexistence of Superconductivity and Topological Order in the Bi ₂ Se ₃ Thin Films

TLDR

Three‑dimensional topological insulators possess nontrivial surface states with spin–momentum locking protected by time‑reversal symmetry, and their topologically ordered phase does not break symmetry, making their interplay with symmetry‑breaking phenomena such as superconductivity a fertile ground for novel quantum effects. The study aims to explore the coexistence of superconductivity and topological order in Bi₂Se₃ thin films. We fabricated a superconducting TI/superconductor heterostructure by growing Bi₂Se₃ thin films on a niobium diselenide substrate, and used scanning tunneling microscopy and angle‑resolved photoemission spectroscopy to observe a superconducting gap at the Bi₂Se₃ surface in thickness regimes where topological surface states form. The observation of a superconducting gap on the Bi₂Se₃ surface in the topological regime provides a platform for realizing Majorana fermions in condensed matter.

Abstract

Three-dimensional topological insulators (TIs) are characterized by their nontrivial surface states, in which electrons have their spin locked at a right angle to their momentum under the protection of time-reversal symmetry. The topologically ordered phase in TIs does not break any symmetry. The interplay between topological order and symmetry breaking, such as that observed in superconductivity, can lead to new quantum phenomena and devices. We fabricated a superconducting TI/superconductor heterostructure by growing dibismuth triselenide (Bi(2)Se(3)) thin films on superconductor niobium diselenide substrate. Using scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we observed the superconducting gap at the Bi(2)Se(3) surface in the regime of Bi(2)Se(3) film thickness where topological surface states form. This observation lays the groundwork for experimentally realizing Majorana fermions in condensed matter physics.