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

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.

5 pages, 5 figures, supplemental material, published in Phys. Rev. B