Superconductivity and fluctuating magnetism in quasi two-dimensional kappa-(BEDT-TTF)2Cu[N(CN)2]Br probed with implanted muons

TL;DR

This study uses muon-spin relaxation to explore superconductivity and magnetic fluctuations in a quasi-two-dimensional organic superconductor, revealing phase separation, vortex behavior, and temperature-dependent magnetic properties.

Contribution

It provides new insights into phase separation, vortex dynamics, and magnetic fluctuations in kappa-(BEDT-TTF)2Cu[N(CN)2]Br using muSR techniques.

Findings

Evidence of low-temperature phase separation with partial superconductivity.

Measurement of in-plane penetration depth as 0.47 μm.

Observation of vortex decoupling transition above 40 mT.

Abstract

A muon-spin relaxation (muSR) investigation is presented for the molecular superconductor kappa-(BEDT-TTF)2Cu[N(CN)2Br]. Evidence is found for low-temperature phase-separation, with only a fraction of the sample showing a superconducting signal, even for slow cooling. Rapid cooling reduces the superconducting fraction still further. For the superconducting phase, the in-plane penetration depth is measured to be lambda_{parallel} = 0.47(1) mu m and evidence is seen for a vortex decoupling transition in applied fields above 40 mT. The magnetic fluctuations in the normal state produce Korringa behavior of the muon spin relaxation rate below 100 K, a precipitous drop in relaxation rate is seen at higher temperatures and an enhanced local spin susceptibility occurs just above T_c.