Hints of granular superconductivity in natural graphite verified by trapped flux transport measurements

Abstract

This study describes electrical transport measurements as a function of magnetic field and temperature that provide hints of the existence of superconductivity with a critical temperature of T c ∼ 350 K in a natural graphite sample. The measurements were done in a restricted temperature 300 K ⩽ T ⩽ 450 K and magnetic field B ⩽ 400 mT range. Electrical resistance measurements at remanence (zero field), after the application of a magnetic field, indicate the existence of trapped flux, which remains nearly unchanged within ∼ 30 min but it vanishes at a temperature of ∼ 330 K. The apparent transition is accompanied by a clear enhancement of the magnetoresistance at T < T c . Raman measurements on the bulk sample reveal the existence of the rhombohedral stacking order, which interfaces with the usual Bernal phase were predicted to lead to high temperature superconductivity due to the formation of robust flat bands in the electron dispersion relation.

Local stabilization of body-centred tetragonal Fe and enhanced dislocation density in carbon nanotubes filled with μm-long nanowires

“…Recent works performed on pyrolytic graphite samples have shown that stacking faults may consist of complex interfaces, comprising either coexisting Bernal (2H) and rhombohedral 3R stacking-order regions, [1][2][3][4] or rotated domains and twistedinterfaces in multilayer graphene. 2,4,5,10,20 Stabilization of the rhombohedral phase has been shown in graphite within defective-structures consisting of staircase morphologies. 10 Implementation of this phase into nanoscale structures and carbon nanotubes is of importance for possible applications in nanoelectronics.…”

“…The possibilities of stabilizing stacking-faults and non-equilibrium structural phases (i.e. rhombohedral domains) within low dimensional carbons, including quasi-two dimensional, [1][2][3][4][5][6][7][8][9][10] two dimensional [11][12][13] and modified one-dimensional systems 14 have recently attracted a great attention for possible applicability in superconductivity. In particular, structural modification of the multilayered structure of the CNT represents an innovative direction for the applicability of CNT systems in superconductivity.…”