Two distinct superconducting states controlled by orientation of local wrinkles in LiFeAs

TL;DR

This study reveals that local surface wrinkles in LiFeAs can induce two distinct superconducting states, with their orientation controlling whether the superconducting gap is enhanced or suppressed, highlighting strain's role in superconductivity.

Contribution

We demonstrate that local wrinkle orientation in LiFeAs controls superconducting properties, revealing strain-induced switching between two superconducting states.

Findings

Type-I wrinkles enlarge superconducting gaps and increase transition temperature.

Type-II wrinkles suppress superconducting gaps.

Superconductivity switches discontinuously at wrinkle borders.

Abstract

We observe two types of superconducting states controlled by orientations of local wrinkles on the surface of LiFeAs. Using scanning tunneling microscopy/spectroscopy, we find type-I wrinkles enlarge the superconducting gaps and enhance the transition temperature, whereas type-II wrinkles significantly suppress the superconducting gaps. The vortices on wrinkles show a C2 symmetry, indicating the strain effects on the wrinkles. A discontinuous switch of superconductivity occurs at the border between two different wrinkles. Our results demonstrate that the local strain effect could affect superconducting order parameter of LiFeAs with a possible Lifshitz transition, by alternating crystal structure in different directions.