Superconducting properties of single-crystalline A_{x}Fe_{2-y}Se_{2} (A=Rb, K) studied using muon spin spectroscopy

TL;DR

This study investigates the superconducting and magnetic properties of single-crystalline A_{x}Fe_{2-y}Se_{2} (A=Rb, K) using muon spin spectroscopy, revealing coexistence or phase separation of magnetism and superconductivity.

Contribution

It provides detailed measurements of magnetic penetration depths and superconducting gaps in Rb and K variants, highlighting their microscopic coexistence or separation.

Findings

Approximately 10% of the sample volume is superconducting.

Superconducting gaps are 7.7 meV for Rb and 6.3 meV for K.

Magnetic penetration depths are 258 nm for Rb and 225 nm for K.

Abstract

We report on the superconducting properties of A_{x}Fe_{2-y}Se_{2} (A = Rb, K) single crystals studied with the muon spin relaxation or rotation (\muSR) technique. At low temperatures, close to 90% of the sample volumes exhibit large-moment magnetic order which impedes the investigation of their superconducting properties by \muSR. On the other hand, about 10% of the sample volumes remain paramagnetic and clearly show a superconducting response. The temperature dependence of the superconducting carrier density was analyzed within the framework of a single s-wave gap scenario. The zero-temperature values of the in-plane magnetic penetration depths \lambda_{ab}(0) = 258(2) and 225(2) nm and the superconducting gaps \Delta(0) = 7.7(2) and 6.3(2) meV have been determined for A = Rb and K, respectively. The microscopic coexistence and/or phase separation of superconductivity and magnetism is discussed.