Hybrid Symmetry Epitaxy of the Superconducting Fe(Te,Se) Film on a Topological Insulator

Abstract

It is challenging to grow an epitaxial 4-fold compound superconductor (SC) on a 6-fold topological insulator (TI) platform due to the stringent lattice-matching requirement. Here, we demonstrate that Fe(Te,Se) can grow epitaxially on a TI (Bi₂Te₃) layer due to accidental, uniaxial lattice match, which is dubbed as "hybrid symmetry epitaxy". This new growth mode is critical to stabilizing robust superconductivity with <i>T</i>_<i>C</i> as high as 13 K. Furthermore, the superconductivity in this FeTe_1-<i>x</i>Se_<i>x</i>/Bi₂Te₃ system survives in the Te-rich phase with Se content as low as <i>x</i> = 0.03 but vanishes at Se content above <i>x</i> = 0.56, exhibiting a phase diagram that is quite different from that of the conventional Fe(Te,Se) systems. This unique heterostructure platform that can be formed in both TI-on-SC and SC-on-TI sequences opens a route to unprecedented topological heterostructures.