Hysteretic superconducting resistive transition in Ba0.07K0.93Fe2As2

TL;DR

This study reports hysteresis in the resistive transition of Ba0.07K0.93Fe2As2 below 1 K under in-plane magnetic fields, indicating a possible first-order transition driven by paramagnetic effects.

Contribution

It provides experimental evidence of hysteresis and first-order transition behavior in this iron-based superconductor related to paramagnetic effects.

Findings

Hysteresis observed below 1 K for in-plane fields

Hysteresis disappears when field is tilted more than 20° from the ab plane

Strong paramagnetic effects influence the superconducting transition

Abstract

We have observed hysteresis in superconducting resistive transition curves of Ba$_{0.07}$K$_{0.93}$Fe$_2$As$_2$ ($T_c\sim$8 K) below about 1 K for in-plane fields. The hysteresis is not observed as the field is tilted away from the $ab$ plane by 20$^{\circ}$ or more. The temperature and angle dependences of the upper critical field indicate a strong paramagnetic effect for in-plane fields. We suggest that the hysteresis can be attributed to a first-order superconducting transition due to the paramagnetic effect. Magnetic torque data are also shown.