Microscopic observation of superconducting fluctuations in $\kappa$-(BEDT-TTF)${}_2$Cu[N(CN)${}_2$]Br by ${}^{13}$C NMR spectroscopy

Abstract

We performed ${}^{13}$C-NMR experiment and measured spin-lattice relaxation rate divided by temperature $1/T_{1}T$ near the superconducting (SC) transition temperature $T_c$ in $\kappa$-(BEDT-TTF)${}_2$Cu[N(CN)${}_2$]Br ($\kappa$-Br salt), and $\kappa$-(BEDT-TTF)${}_2$Cu(NCS)${}_2$ ($\kappa$-NCS salt). We observed the reduction of $1/T_{1}T$ starting at the temperature higher than $T_c$ in $\kappa$-Br salt. Microscopic observation of quasi-particle density of states in the fluctuating SC state revealed the effects of short-range Cooper pairs induced in the normal state to the quasi-particle density of states. We also performed systematic measurements in the fields both parallel and perpendicular to the conduction plane in $\kappa$-Br and $\kappa$-NCS salts, and confirmed that the reduction of $1/T_{1}T$ above $T_c$ is observed only in $\kappa$-Br salt regardless of the external field orientation.

arXiv commentAccepted for publication in PRB

References in corpus (3)

• Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-2D organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br: quest for intrinsic scattering contributions
• Superconducting Fluctuation Effects on the Spin-Lattice Relaxation Rate in YBa_2Cu_3O_{6.95}
• Superconducting fluctuations and anomalous diamagnetism in underdoped YBa2Cu3O6+x from magnetization and 63Cu NMR-NQR relaxation measurements

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