Partially-ordered vortex lattices in the high-field, low-temperature mixed state of quasi two-dimensional organic superconductors

TL;DR

This study uses MuSR measurements to reveal partially-ordered vortex lattice phases in high-field, low-temperature quasi-2D organic superconductors, indicating vortex-lattice melting and strong flux pinning effects.

Contribution

First experimental evidence of partially-ordered vortex lattices in these organic superconductors at high magnetic fields.

Findings

Vortex lattice phases exist up to 2.5 T and 4 T in the studied compounds.

Sharp loss of order suggests vortex-lattice melting transition.

Strong flux-line pinning may stabilize the vortex phases.

Abstract

We report the results of high-field, low-temperature MuSR measurements of the quasi two-dimensional organic superconductors \k{appa}-(ET)2Cu(NCS)2 and \k{appa}-(ET)2Cu[N(CN)2]Br. The MuSR lineshapes for these compounds indicate the existence of partially-ordered vortex lattice phases in the high magnetic field regime, up to 2.5 T for the former compound and 4 T for the latter compound. The observed sharp loss of order is found to be consistent with a vortex-lattice melting transition that is predicted by numerical simulations of weakly coupled layers of pancake vortices. It is argued that the robustness of the partially-ordered vortex lattice phases could be due to strong flux-line pinning by a dilute ensemble of defects.