Global room-temperature superconductivity in graphite

TL;DR

This paper reports the observation of global room-temperature superconductivity in graphite with surface line defects, supported by experimental measurements and a developed theoretical model explaining the phase coherence in defect arrays.

Contribution

It provides the first experimental evidence and theoretical explanation of room-temperature superconductivity in graphite induced by surface defects.

Findings

Superconductivity observed at temperatures above 300 K.

Critical current I_c(T,B) inversely proportional to normal state resistance R_N(T,B).

Superconducting screening and Josephson effects confirmed.

Abstract

Room temperature superconductivity under normal conditions has been a major challenge of physics and material science since its very discovery. Here we report the global room-temperature superconductivity observed in cleaved highly oriented pyrolytic graphite carrying dense arrays of nearly parallel surface line defects. The multiterminal measurements performed at the ambient pressure in the temperature interval 4.5 K < T < 300 K and at magnetic fields 0 < B < 9 T applied perpendicular to the basal graphitic planes reveal that the superconducting critical current I_c(T,B) is governed by the normal state resistance RN(T, B) so that I_c(T,B) is proportional to 1/R_N(T, B). Magnetization M(T, B) measurements of superconducting screening and hysteresis loops together with the critical current oscillations with temperature that are characteristic for superconductor-ferromagnet-superconductor Josephson chains, provide strong support for occurrence of superconductivity at T > 300 K. We develop a theory of global superconductivity emerging in the array of linear structural defects which well describes the experimental findings and demonstrate that global superconductivity arises as a global phase coherence of superconducting granules in linear defects promoted by the stabilizing effect of underlying Bernal graphite via tunneling coupling to the three dimensional (3D) material.