Local density of states in the superconductor $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br

TL;DR

This study uses low temperature scanning tunneling spectroscopy to analyze the local density of states in the organic superconductor $ layers, confirming superconductivity is confined to these layers with a two-gap density of states.

Contribution

It provides direct experimental evidence of the layered structure's role in superconductivity and identifies a twofold superconducting gap related to the Fermi surface bands.

Findings

Superconductivity is confined to BEDT-TTF layers.

Density of states shows a twofold superconducting gap.

Superconducting gap attributed to two separated bands crossing the Fermi surface.

Abstract

Low temperature scanning tunneling spectroscopy reveals the local density of states of the organic superconductor $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br, that was cut in-situ in ultra-high vacuum perpendicular to the superconducting BEDT-TTF layers. The spectra confirm that superconductivity is confined to the conducting BEDT-TTF layers, while the Cu[N(CN)$_2$]Br anion layers are insulating. The density of states comprises a twofold superconducting gap, which is attributed to the two separated bands crossing the Fermi surface.