Scanning Tunneling Spectroscopy on the novel superconductor CaC6

TL;DR

This study uses scanning tunneling spectroscopy to investigate the superconducting properties of CaC6, revealing a BCS-like gap, vortex imaging, and coherence length measurement.

Contribution

First detailed tunneling spectroscopy analysis of CaC6 revealing its superconducting gap and vortex structure.

Findings

Superconducting gap consistent with BCS theory (1.6 meV)

Vortex imaging shows a coherence length of approximately 33 nm

Discussion of potential gap anisotropy and two-gap behavior

Abstract

We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC$_6$. The tunneling conductance spectra, measured between 3 K and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with $\Delta(0)$ = 1.6 $\pm$ 0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows to deduce a coherence length in the ab plane $\xi_{ab}\simeq$ 33 nm.