ac strain based thermodynamic criterion for vortex lattice in type-II superconductors

TL;DR

This paper introduces a novel ac strain susceptibility method to identify vortex lattice phases in type-II superconductors, revealing a magnetoelastic property and providing a thermodynamic criterion for phase detection.

Contribution

The study discovers a dynamic magnetostrictive effect that serves as a new thermodynamic criterion for identifying vortex lattice phases in type-II superconductors.

Findings

Signal amplitude correlates linearly with vortex density.

Signal decays near the upper critical field Hc2.

Out-of-phase component indicates increased dissipation in vortex liquid phase.

Abstract

In type-I superconductors, zero electrical resistivity and perfect diamagnetism define two fundamental criteria for superconducting behavior. In contrast, type-II superconductors exhibit more complex mixed state physics, where magnetic flux penetrates the material above the lower critical field Hc1 in the form of quantized vortices, each carrying a single flux quantum. These vortices form a two dimensional lattice which persists up to another irreversible field (Hirr) and then melts into a dissipative liquid phase. The vortex lattice is fundamental to the magnetic and electrical properties of type II superconductors, ac strain susceptibility-a thermodynamic criterion-for identifying this phase has remained elusive. Here, we report the discovery of a dynamic magnetostrictive effect, wherein the geometry of the superconductor oscillates only under an applied alternating magnetic field due to the disturbance of the vortex lattice. This effect is detected by a thin piezoelectric transducer, which converts the excited geometric deformation into an in-phase ac voltage. Notably, we find a direct and nearly linear relationship between the signal amplitude and the vortex density in lattice across several representative type-II superconductors. In the vortex liquid phase above Hirr, the signal amplitude rapidly decays to zero near the upper critical field (Hc2), accompanied by a pronounced out-of-phase component due to enhanced dissipation. This dynamic magnetostrictive effect not only reveals an unexplored magnetoelastic property of the vortex lattice but also establishes a fundamental criterion for identifying the type-II superconductors.