Universal Lower Limit on Vortex Creep in Superconductors

TL;DR

This paper establishes a universal lower limit on vortex creep rates in superconductors, revealing a fundamental constraint that influences material design and understanding of vortex dynamics across different superconducting systems.

Contribution

It introduces the concept of a universal minimum vortex creep rate in superconductors, supported by experimental evidence from BaFe2(As0.67P0.33)2 films and other materials.

Findings

Very slow vortex creep observed in BaFe2(As0.67P0.33)2 films

Proposed existence of a universal minimum vortex creep rate

No material has been observed to violate this lower limit

Abstract

Superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals, and Bose-Einstein condensates. Vortex motion can be disruptive; it can cause phase transitions, glitches in pulsars, and losses in superconducting microwave circuits, and it limits the current carrying capacity of superconductors. Understanding vortex dynamics is therefore of fundamental and technological importance, and the competition between the effects of thermal energy and energy barriers defined by material disorder is not completely understood. In particular, early measurements of thermally-activated vortex motion (creep) in iron-based superconductors unveiled fast rates (S) comparable to measurements of YBa2Cu3O7 (YBCO). This was puzzling because S is thought to somehow positively correlate with the Ginzburg number (Gi), and Gi is orders of magnitude lower in most iron-based superconductors than in YBCO. Here, we report very slow creep in BaFe2(As0.67P0.33)2 films, and propose that there is a universal minimum realizable (where Tc is the superconducting transition temperature) that has been achieved in our films, few other materials, and violated by none. This limitation provides new clues on how to design materials with slow creep and helps elucidate open questions regarding the interplay between system-specific length scales and vortex dynamics.