Paramagnetic limiting of the upper critical field of the layered organic superconductor $\kappa -(BEDT-TTF)_2Cu(SCN)_2$

TL;DR

This study measures the upper critical magnetic field of a layered organic superconductor, revealing its behavior near the paramagnetic limit and showing layer decoupling effects.

Contribution

It provides detailed experimental data on the upper critical field and its angular dependence, highlighting deviations from BCS theory and insights into layer decoupling.

Findings

Upper critical field increases linearly with decreasing temperature for fields parallel to layers.

Measured critical field exceeds BCS paramagnetic limit but aligns with thermodynamic estimates.

Angular dependence shows a cusp-like feature indicating layer decoupling.

Abstract

We report detailed measurements of the interlayer magnetoresistance of the layered organic superconductor $\kappa -(BEDT-TTF)_2Cu(SCN)_2$ for temperatures down to 0.5 K and fields up to 30 tesla. The upper critical field is determined from the resistive transition for a wide range of temperatures and field directions. For magnetic fields parallel to the layers, the upper critical field increases approximately linearly with decreasing temperature. The upper critical field at low temperatures is compared to the Pauli paramagnetic limit, at which singlet superconductivity should be destroyed by the Zeeman splitting of the electron spins. The measured value is comparable to a value for the paramagnetic limit calculated from thermodynamic quantities but exceeds the limit calculated from BCS theory. The angular dependence of the upper critical field shows a cusp-like feature for fields close to the layers, consistent with decoupled layers.