Interfacially Enhanced Superconductivity in Fe(Te,Se)/Bi₄Te₃ Heterostructures.

Abstract

Realizing topological superconductivity by integrating high-transition-temperature (T_C) superconductors with topological insulators can open new paths for quantum computing applications. Here, a new approach is reported for increasing the superconducting transition temperature <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mo>(</mo> <msubsup><mi>T</mi> <mi>C</mi> <mi>onset</mi></msubsup> <mo>)</mo></mrow> <annotation>$( {T_{\mathrm{C}}^{{\mathrm{onset}}}} )$</annotation></semantics> </math> by interfacing the unconventional superconductor Fe(Te,Se) with the topological insulator Bi-Te system in the low-Se doping regime, near where superconductivity vanishes in the bulk. The critical finding is that the <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msubsup><mi>T</mi> <mi>C</mi> <mi>onset</mi></msubsup> <annotation>$T_{\mathrm{C}}^{{\mathrm{onset}}}$</annotation></semantics> </math> of Fe(Te,Se) increases from nominally non-superconducting to as high as 12.5 K when Bi₂Te₃ is replaced with the topological phase Bi₄Te₃. Interfacing Fe(Te,Se) with Bi₄Te₃ is also found to be critical for stabilizing superconductivity in monolayer films where <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msubsup><mi>T</mi> <mi>C</mi> <mi>onset</mi></msubsup> <annotation>$T_{\mathrm{C}}^{{\mathrm{onset}}}$</annotation></semantics> </math> can be as high as 6 K. Measurements of the electronic and crystalline structure of the Bi₄Te₃ layer reveal that a large electron transfer, epitaxial strain, and novel chemical reduction processes are critical factors for the enhancement of superconductivity. This novel route for enhancing T_C in an important epitaxial system provides new insight on the nature of interfacial superconductivity and a platform to identify and utilize new electronic phases.