Pressure-induced superconductivity in Bi4(I1−x Br x )4 crystals grown by chemical vapor transport and flux methods

Abstract

Achieving superconductivity in topological materials is thought as a promising route for realizing topological superconductivity, which may provide potential applications to quantum computation. Previously, rich superconducting phases have been reported in the pressurized Bi4I4 and Bi4Br4 crystals which belong to an interesting quasi-one-dimensional topological system. In this work, we have performed a high-pressure study on some Bi4(I1−x Br x )4 crystals grown by two different methods. Remarkably, crystals grown by the chemical vapor transport (CVT) method and the self-flux method show clearly different pressure effects. In the CVT-grown crystals, only one superconducting transition is observed, while three superconducting transitions can be detected in crystals grown by the flux method. Through comparisons of the pressure-dependent phase diagrams and the upper critical field behaviors in the two kinds of crystals, the higher superconducting transition (>6 K) in the flux-grown crystals is suggested to come from the residual Bi. High-pressure Raman spectroscopy measurements on both kinds of crystals have confirmed the occurrence of a similar structural transition around 10 GPa in Br-doped samples. Overall, our data could be helpful for identifying the intrinsic pressure-induced superconductivity in various Bi-based materials.