Superconductivity and fluctuating magnetism in quasi-two-dimensionalκ-(BEDT-TTF)2Cu[N(CN)

Abstract

A muon-spin relaxation (µ + SR) investigation is presented for the molecular superconductor κ-(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 λ = 0.47(1) µm 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 Tc.

Low-Field Superconducting Phase of(TMTSF)2ClO4

“…Transverse-field (TF) SR provides a means of accurately measuring the internal magnetic-field distribution caused by the vortex lattice (VL) in a type-II SC [16] and has previously proven useful in establishing the vortex properties of molecular SCs [17,18]. Our field-cooled TF SR measurements used two þ SR instruments.…”

“…The melting curve at low H takes the form [24] T m ðHÞ¼T c ð0Þ=½1þðH=H 0 Þ 1=2 , where H 0 is a characteristic field. In highly 2D systems such as -ET, fieldinduced layer decoupling transitions dominate over 3D melting [18,22], but strong Josephson coupling for TMC stabilizes the layers against this decoupling.…”

Stretched exponential spin relaxation in organic superconductors

“…Interestingly, recent μSR measurements of the local electronic spin susceptiblity in κ-(ET) 2 Cu[N(CN) 2 ]Br exhibit a sharp peak near 15K and extending up to ~ 25K [54].…”

Odd-frequency pairing in (TMTSF)2ClO4

“…Transverse field muon spin rotation (TF µSR) provides a means of accurately measuring the internal magnetic field distribution caused by the vortex lattice (VL) in a type II SC 16 and has previously proven useful in establishing the vortex properties of molecular SCs 17,18 . Our field-cooled TF µSR measurements used two µ + SR instruments.…”

“…The melting curve at low H takes the form 24 T m (H) = T c (0)/(1 + (H/H 0 ) 1/2 ) where H 0 is a characteristic field. In highly 2D systems such as κ-ET, field-induced layer decoupling transitions dominate over 3D melting 18,22 , but strong Josephson coupling stabilises the layers for TMC.…”