Probing superconducting anisotropy of single crystal KCa2Fe4As4F2 by magnetic torque measurements

Abstract

Anisotropy is the key to understanding iron-based superconductors, which usually have quasi-two dimensional layered structures. By using torque measurements (a sensitive tool to detect the magnetic anisotropy), we investigate the superconducting anisotropy of the KCa2Fe4As4F2 (12442, T-c = 33 K) single crystal. In the normal state, the torque data display a paramagnetic behavior H-2 sin 2 theta in different applied magnetic fields H aligned at an angle theta to the c axis of the crystal, while in the mixed state vortex torque dominates the torque signal. The anisotropy parameter. and London penetration depth. were obtained from vortex torque analyzed using Kogan's formula. It was found that gamma is 16.2 at T = 25 K (approximate to 0.76 T-c), close to gamma approximate to 15 at T approximate to 0.76 T-c for CaFe0.88Co0.12AsF, but much larger than the result of 11 and 122 families, where gamma is around 3. In addition, the obtained perpetration depth from the torque measurements is consistent with the results of mu SR measurements of KCa2Fe4As4F2. Our results suggest that the two-dimensionality plays a vital role in the superconductivity of the 12442-type iron-based superconductor.