Superconductivity problems with multiple Ginzburg-Landau order parameters

[摘要] ENGLISH ABSTRACT: Two problems in the field of materials-based condensed matter physics, specifically in the fieldof superconductivity, are studied theoretically. In both problems, where each is of current exper-imental interest, an extension of Ginzburg-Landau theory is used to describe a physical system,with focus on the energy associated to the interface(s) occurring in the respective systems.The first physical system under consideration is that of a two-band superconductor. UsingGinzburg-Landau theory for two-band superconductors, the interface energy ¾s between normaland superconducting states coexisting at the thermodynamic critical magnetic field is determined.From the theoretical and numerical analysis of the interface energy, it is found that close to thetransition temperature, where the Ginzburg-Landau theory is applicable, the two-band problemmaps onto an effective single band problem. This finding puts into question the possibility ofintermediate, so called type-1.5 superconductivity, in the regime where the Ginzburg-Landautheory applies.The second physical system is that of a system with competing superconductivity and anti-ferromagnetism. From Ginzburg-Landau theory for such competing systems in a thermodynamiccritical magnetic field, it is shown that two possible interfaces can occur: an interface betweena pure anti-ferromagnetic state and a pure superconducting state; and an interface between astate with coexisting superconductivity and anti-ferromagnetism and a pure anti-ferromagneticstate. The energy associated to both these interfaces is analysed theoretically and numericallyfrom which the boundary between type-I and type-II superconductivity is obtained for certainspecific cases.

[发布机构] Stellenbosch University