Stanford Synchrotron Radiation Lightsource

Pablo Esquinazi, University of Leipzig

We review different experimental results that indicate the existence of granular superconductivity at high temperatures at graphite interfaces. In particular we will discuss the following experimental results:

• The temperature and magnetic field dependence of the electrical resistance of bulk and thin graphite samples and its relation with the existence of two-dimensional (2D) interfaces.
• The anomalous hysteresis in the magnetoresistance observed in graphite thin samples as well as its enhancement restricting the current path within the sample.
• The Josephson behavior of the current-voltage characteristics with zero resistance states at high temperatures in especially prepared TEM lamellae.
• The magnetization of bulk graphite samples with and without interfaces [6] as well as water treated graphite powders [7]. Special emphasis will be given to the possible ways to differentiate between ferromagnetic- from superconducting-like signals when the magnetic moments of interest remain small in comparison with the large diamagnetic backgrounds.
• Recently done transport and persistent currents experiments at room temperature on graphite flakes embedded in alkanes and their reproducibility.

All the experimental evidence as a whole suggests the existence of superconductivity at very high temperatures in regions located at certain surfaces or interfaces between semiconducting crystalline regions with Bernal stacking order inside graphite samples. Recently published theoretical works [9,10] that provide a possible origin for the quasi 2D superconductivity at high temperatures in graphite samples will be shortly discussed.