Strain-induced Berry phase in chiral superconductors

TL;DR

This paper investigates how in-plane strain in a chiral $p_x+ip_y$ superconductor induces a Berry phase in the order parameter, revealing topological effects observable in vortex behavior and critical fields.

Contribution

It demonstrates that strain can generate a Berry phase in the superconductor's order parameter, linking topological properties to measurable physical signatures.

Findings

Berry phase of π acquired under strain cycles

Topological signature in superfluid stiffness tensor

Observable effects on vortices and critical fields

Abstract

We study the topology of the order parameter in the intermediate phase between the superconducting and time-reversal symmetry breaking transitions of a $p_x+ip_y$ superconductor under strain. The application of in-plane strain reduces the underlying crystal symmetry and lifts the degeneracy of the critical temperature between the $p_x$ and $p_y$ orbitals, resulting in a Dirac cone structure in the thermodynamic phase diagram. When the strain is varied adiabatically along a closed path enclosing the Dirac cone, the order parameter acquires a Berry phase of $\pi$, which originates from a half rotation of the superconducting gap function. This half rotation leaves a topological signature in the superfluid stiffness tensor, making it directly observable through the geometry of vortices and the upper critical field.