Upper Critical Fields and Anisotropy of Ca1-xLaxFe2As2 Single Crystals

TL;DR

This study investigates the superconducting properties, critical fields, and anisotropy of Ca1-xLaxFe2As2 single crystals across various doping levels, revealing complex phase diagrams and large anisotropies potentially linked to interface effects.

Contribution

It provides detailed phase diagrams and anisotropy measurements for Ca1-xLaxFe2As2, highlighting the coexistence of two superconducting phases and their distinct magnetic responses.

Findings

Observation of double superconducting transitions in medium-doped samples

Identification of two distinct Hc2 phase diagrams for different Tc regimes

Large anisotropies in superconducting phases suggesting interface or intercalation effects

Abstract

Superconductivity of Ca1-xLaxFe2As2 single crystals with various doping level were investigated via electromagnetic measurements for out-plane (H//c) and in-plane (H//ab) directions. Obvious double superconducting transitions, which can survive in magnetic fields up to several Tesla, were observed in the medium-doped (x = 0.13) sample. Two kinds of distinct Hc2 phase diagrams were established for the low superconducting phase with Tc lower than 15 K and the high superconducting phase with Tc of over 40 K, respectively. Both the two kinds of phase diagrams exist in the medium-doped sample. Unusual upward curvature near Tc was observed in Hc2 phase diagrams and analyzed in detail. Temperature dependences of anisotropy for different doping concentrations were obtained and compared. Both superconducting phases manifest extremely large anisotropies, which may originate from the interface or intercalation superconductivity.