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We report proximity-induced superconducting features over macroscopic lengths in highly oriented pyrolytic graphite. The phenomenon is triggered when electrical currents are injected in the material through superconducting electrodes, few millimeters apart from each other. Such a large range is anomalous, as proximity-induced features in normal conductors hardly surpass few micrometers. The results can be explained as due to the presence of pre-existing superconductivity in graphite on small, localized regions.

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We have observed superconductivity in heavy p-doped Ge by measuring of differential resistance dV/ dI( V) of Ge–PtIr point contacts. The superconducting features disappear above 6 K or above 1 T, what can be taken as the critical temperature and the critical magnetic field, respectively. The observed dV/ dI( V) spectrum with Andreev reflection like features was fitted within one-gap Blonder–Tinkham–Klapwijk model. The extracted superconducting gap demonstrates Bardeen–Cooper–Schrieffer-like behavior with 2Δ/ kBTc = 10.5 ± 0.5 ratio, which is much higher than expected for conventional superconductors. Magnetic field suppresses Andreev reflection features, but the superconducting gap moderately decreases in magnetic field similarly as it was observed previously for the type II superconductors, including nickel borocarbide and iron-based superconductors. Curiously, we have not yet observed superconductivity in n-doped Ge with a similar dopant concentration.

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