Some metals demonstrate infinite conductivity (zero resistance) at temperatures below some critical temperature T c , see Fig. 7.1. At T > T c the metals behave as normal. This effect is called superconductivity (H. K. Onnes, 1911) and the corresponding metals are superconductors. T c varies widely for different metals (Rh: 0.001 K; Ti: 0.39 K; Al: 1.14 K; V: 5.38 K; Nb: 9.5 K; Nb3Sn: 18.05 K; Nb3Ge: 23.2 K; YBa2Cu3O7—δ: 90 K). At T > T c we talk about normal and when T < T c — superconducting states of these metals.
KeywordsEntropy Anisotropy Graphite Hexagonal Coherence
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