Tunneling spectroscopy of Na$_{x}$CoO$_2$ and Na$_{x}$CoO$_2$$\cdot$ yH$_2$O

TL;DR

This study uses tunneling spectroscopy to investigate the electronic properties of Na$_{x}$CoO$_2$ and its hydrated superconductor, revealing spatial variability in the non-superconducting phase and pseudogap-like features in the superconducting phase.

Contribution

It provides the first tunneling spectroscopy data on Na$_{x}$CoO$_2$·yH$_2$O, highlighting the reproducibility of superconducting spectra and identifying pseudogap-like behavior.

Findings

Spectra of Na$_{x}$CoO$_2$ show non-uniform shapes due to sodium distribution.

Superconducting samples exhibit reproducible spectra with zero bias conductance depression.

The conductance depression appears below an onset temperature around 45 K, similar to pseudogap features in cuprates.

Abstract

The single electron tunneling spectroscopy on superconductor Na$_{x}$CoO$_2$$\cdot$ yH$_2$O and its starting compound Na$_{x}$CoO$_2$ has been studied with point-contact method. The spectra of Na$_{x}$CoO$_2$ have two types of distinct shapes at different random locations, this is attributed to the non-uniformly distributed sodium escaped from the inner part of the sample. While all the measured spectra of the superconducting samples Na$_{x}$CoO$_2$$\cdot$ yH$_2$O have a good spatial reproducibility, and show a remarkable zero bias conductance depression appearing below an onset temperature which associates very well with the resistance upturn at around 45 K. The latter behavior resembles in some way the pseudogap feature in high-T$_c$ cuprate uperconductors.