Evidence for room temperature superconductivity at graphite interfaces

摘要

In the last 43 years several hints were reported suggesting the existence ofgranular superconductivity above room temperature in different graphite-basedsystems. In this paper some of the results are reviewed, giving specialattention to those obtained in water and n-heptane treated graphite powders,commercial and natural bulk graphite samples with different characteristics aswell as transmission electron microscope (TEM) lamellae. The overall resultsindicate that superconducting regions exist and are localized at certaininternal interfaces of the graphite structure. The existence of therhombohedral graphite phase in all samples with superconducting-like propertiessuggests its interfaces with the Bernal phase as a possible origin for thehigh-temperature superconductivity, as theoretical calculations predict. Highprecision electrical resistance and magnetization measurements were used toidentify a transition at $T_c \gtrsim 350~$K. To check for the existence oftrue zero resistance paths in the samples we used local magnetic measurements,which results support the existence of superconducting regions at such hightemperatures.