Mutual influence of superconducting and structure phase transitions

Based on the phenomenological theory of second-order transitions and an extended Ginzburg–Landau theory, which accounts for the crystal symmetry of the superconductor, we study the mutual influence of superconducting and structure phase transitions. Transitions without changes of the Bravais lattice are considered. As an example we study the phase transitions in materials of tetragonal symmetry. Possible phase transformations and their dependence on the temperature and the intensity of the “interaction” between superconducting and structure properties have been investigated. It is shown that a structure transformation can either promote superconductivity or suppress it as well, and vice versa, the superconducting state can significantly influence the lattice stability against structure changes.