In-plane superfluid density and microwave conductivity of the organic superconductor \kappa-(BEDT-TTF)2Cu[N(CN)2]Br: evidence for d-wave pairing and resilient quasiparticles

TL;DR

This study provides evidence for d-wave pairing in -(BEDT-TTF)2Cu[N(CN)2]Br through microwave measurements, revealing resilient quasiparticles and Fermi liquid behavior in the normal state.

Contribution

It presents the first microwave surface impedance measurements on this organic superconductor, demonstrating d-wave pairing signatures and resilient quasiparticles.

Findings

Linear temperature dependence of superfluid density

Quasiparticle scattering rate  T^3 in the superconducting state

Absence of BCS coherence peak in conductivity

Abstract

We report the in-plane microwave surface impedance of a high quality single crystal of \kappa-(BEDT-TTF)2Cu[N(CN)2]Br. In the superconducting state, we find three independent signatures of d-wave pairing: i) a strong, linear temperature dependence of superfluid density; ii) deep in the superconducting state the quasiparticle scattering rate \Gamma ~ T^3; and iii) no BCS coherence peak is observed in the quasiparticle conductivity. Above T_c, the Kadowaki-Woods ratio and the temperature dependence of the in-plane conductivity show that the normal state is a Fermi liquid below ~ 23 K, yet resilient quasiparticles dominate the transport up to ~ 50 K.