Critical fields, thermally-activated transport and critical current density of beta-FeSe single crystals

TL;DR

This study investigates the critical magnetic fields, flux flow behavior, and current-carrying capacity of beta-FeSe single crystals, revealing their type-II superconductivity characteristics and vortex pinning mechanisms.

Contribution

It provides detailed measurements of critical fields, flux flow, and critical current density in beta-FeSe, highlighting its nearly isotropic upper critical fields and vortex pinning behavior.

Findings

Beta-FeSe is a type-II superconductor with a high Ginzburg-Landau parameter (~72.3).

Upper critical fields are nearly isotropic and likely limited by Pauli paramagnetism.

Critical current density is significantly lower than in other iron-based superconductors.

Abstract

We present critical fields, thermally-activated flux flow (TAFF) and critical current density of tetragonal phase beta-FeSe single crystals. The upper critical fields Hc2(T) for H||(101) and H\bot(101) are nearly isotropic and are likely governed by Pauli limiting process. The obtained large Ginzburg-Landau parameter k \sim 72.3(2) indicates that beta-FeSe is a type-II superconductor with smaller penetration depth than in Fe(Te,Se). The resistivity below Tc follows Arrhenius TAFF behavior. For both field directions below 30 kOe single vortex pinning is dominant whereas collective creep becomes important above 30 kOe. The critical current density Jc from M-H loops for H||(101) is about five times larger than for H\bot(101), yet much smaller than in other iron-based superconductors.