A contribution to the phenomenological theory of a two-band crystalline superconductor with tetragonal and orthorhombic symmetry

Crystalline superconductors of tetragonal (point group D4h) and orthorhombic (point group D2h) symmetry with two overlapping conduction bands are considered. The thermodynamic potentials in the vicinity of the critical temperature are obtained and the Ginzburg–Landau equations are derived for superconducting transitions of electrons from both bands associated with all the irreducible representations of groups D4h and D2h. Attention is called to differences in the character of the phase transitions that belong to coincident and different representations. Existence of an interband superconducting current is predicted.

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