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 Bi 4 I 4 and Bi 4 Br 4 crystals which belong to an interesting quasi-one-dimensional topological system. In this work, we have performed a high-pressure study on some Bi 4 (I 1− 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.