Superconducting Sweet-Spot in Microcrystalline Graphite Revealed by Point-Contact Spectroscopy

TL;DR

This study reports the discovery of local superconductivity in micro-crystalline graphite, evidenced by a magnetic field-dependent electronic gap observed through point-contact spectroscopy at low temperatures.

Contribution

It provides experimental evidence of superconductivity in micro-crystalline graphite and characterizes its properties using point-contact spectroscopy and theoretical models.

Findings

Observation of a 4.2 meV gap at zero magnetic field.

Gap closes with increasing magnetic field, consistent with superconductivity.

Estimated critical temperature of 14 K based on BCS theory.

Abstract

In this letter we describe the observation of a magnetic field dependent electronic gap, suggestive of local superconductivity, in the point-contact spectrum of micro-crystalline graphite. Magnetic field dependent point-contact spectroscopy was carried out at a temperature of $1.8\,\mathrm{K}$ using an etched aluminium tip. At zero field a gap structure in the differential conductance is observed, showing a gap of $\Delta = 4.2\,\mathrm{meV}$. On applying magnetic fields of up to $500\,\mathrm{mT}$, this gap gradually closes, following the theoretical prediction by Ginzburg and Landau for a fully flux-penetrated superconductor. By applying BCS-theory, we infer a critical superconducting temperature of $14\,\mathrm{K}$.