Phase transition into the superconducting mixed state and the de Haas-van Alphen effect
Abstract The Landau expansion for the free energy of the superconducting mixed state near the upper critical field in powers of the sauare modulus of the order parameter averaged over an Abrikosov lattice is derived. The analytical calculations have been carried out in the framework of the Gor'kov formalism for a 3-dimensional isotropic BCS model beyond the limits of the quasiclassical approximation, that is, with Landau auantization of the auasiparticle energy levels taken into consideration. The derivation is performed at Iow temperature for finite but high enough crystal purity. The effect of Pauli paramagnetic terms is taken into account. The quantum oscillations of the critical temperature, the order parameter's amplitude and the magnetization (de Haas-van Alphen effect) in the mixed state are found. The limitation for the validity of a mean field approach due to critical fluctuations (Ginzburg criterion) for the phase transition under consideration is established.
Theoretical description of nearly discontinuous transition in superconductors with paramagnetic depairing
Based on a theoretical argument and Monte Carlo simulations of a Ginzburg–Landau model derived microscopically, it is argued that, in type-II superconductors where both the paramagnetic and orbital depairings are important, a strong first-order transition (FOT) at H c2 expected in the mean field (MF) approximation never occurs in real systems and changes due to the fluctuation into a crossover. The present result explains why a nearly discontinuous crossover at H c2 with no intrinsic hysteresis is observed only in a clean superconducting material with a singlet pairing and a high condensation energy such as CeCoIn 5 .
Quantum oscillation measurements of band magnetism in UPt3 and CeRu2Si2
A central enigma of the heavy fermion metals is the dual behaviour of the electrons which, at relatively short time scales, exhibit the properties expected of well-localised moments and, at very long time scales, in cooperation with other valence electrons at low temperatures, display the characteristics of massive itinerant carriers having a sharply defined Fermi surface. Detailed experimental support for the latter (long-time) cooperative behaviour of electrons in UPt3 and CeRu2Si2 has been furnished principally by studies of quantum oscillatory phenomena. In this paper the information provided by these studies is summarized, and recent observations of the evolution of the quasiparticle band structure during the magnetisation process and at the metamagnetic transitions in these materials are described.