Berlin 2018 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 16: Superconductivity: Properties and Electronic Structure II
TT 16.9: Vortrag
Montag, 12. März 2018, 17:15–17:30, H 0110
Experimental evidences of a possible superconducting transition above room temperature in natural graphite crystals — •Christian Eike Precker1, Pablo David Esquinazi1, Markus Stiller1, José Luis Barzola Quiquia1, and Ana Melva Champi Farfan2 — 1Felix-Bloch-Institut, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany. — 2CCNH, Universidade Federal do ABC, São Paulo, Brazil
By use of the four-terminal sensing method and high resolution electrical transport measurement, natural graphite samples from Brazil and Sri Lanka mines were measured. Temperature dependent resistance R(T) measurements shows a step-like transition at T ∼ 350 K. Further experiments were performed, like magnetization and time dependence R(T) after a field change, showing a magnetic irreversibility, i.e. trapped flux and flux creep and partial magnetic flux expulsion. All before mentioned experimental results suggest the existence of granular superconductivity below 350 K. X-rays diffraction measurements proved the existence of rhombohedral graphite phase in all measured samples, suggesting the presence of interfaces formed between the rhombohedral and Bernal phase as responsible for the high-temperature superconductivity, as predicted by theoretical calculations. The measured remanence in the magnetoresistance is due to pinned fluxons produced through superconducting currents. The current path of a graphite sample in remanence state has been measured using magnetic force microscopy. The current path vanished at the same critical temperature measured with the resistance.