Phases and phase transitions in spin-triplet ferromagnetic superconductors

Recent results for the coexistence of ferromagnetism and unconventional superconductivity with spin-triplet Cooper pairing are reviewed on the basis of the quasi-phenomenological Ginzburg-Landau theory. New results are reported. The results are discussed in view of applications to metallic compounds as UGe2, URhGe, ZrZn2.Comment: 32 pages, 5 figs, Miktex; Chapter in ``Progress in Ferromagnetism Research'' (NOVA, N. Y., 2004

New critical behavior in unconventional ferromagnetic superconductors

New critical behavior in unconventional superconductors and superfluids is established and described by the Wilson-Fisher renormalization-group method. For certain ordering symmetries a new type of fluctuation-driven first order phase transitions at finite and zero temperature are predicted. The results can be applied to a wide class of ferromagnetic superconducting and superfluid systems, in particular, to itinerant ferromagnets as UGe2 and URhGe.Comment: 12 pages, 6 fig

Diamagnetic susceptibility of spin-triplet ferromagnetic superconductors

We calculate the diamagnetic susceptibility in zero external magnetic field above the phase transition from ferromagnetic phase to phase of coexistence of ferromagnetic order and unconventional superconductivity. For this aim we use generalized Ginzburg-Landau free energy of unconventional ferromagnetic superconductor with spin-triplet electron pairing. A possible application of the result to some intermetallic compounds is briefly discussed.Comment: 7 pages, 1 figur

About the magnetic fluctuation effect on the phase transition to superconducting state in Al

The free energy and the order parameter profile near the phase transition to the superconducting state in bulk Al samples are calculated within a mean-field-like approximation. The results are compared with those for thin films.Comment: 11 pages, miktex, 2 figure

Structural transitions in vertically and horizontally coupled parabolic channels of Wigner crystals

Structural phase transitions in two vertically or horizontally coupled channels of strongly interacting particles are investigated. The particles are free to move in the $x$-direction but are confined by a parabolic potential in the $y$-direction. They interact with each other through a screened power-law potential ($r^{-n}e^{-r/\lambda}$). In vertically coupled systems the channels are stacked above each other in the direction perpendicular to the $(x,y)$-plane, while in horizontally coupled systems both channels are aligned in the confinement direction. Using Monte Carlo (MC) simulations we obtain the ground state configurations and the structural transitions as a function of the linear particle density and the separation between the channels. At zero temperature the vertically coupled system exhibits a rich phase diagram with continuous and discontinuous transitions. On the other hand the vertically coupled system exhibits only a very limited number of phase transitions due to its symmetry. Further we calculated the normal modes for the Wigner crystals in both cases. From MC simulations we found that in the case of vertically coupled systems the zigzag transition is only possible for low densities. A Ginzburg-Landau theory for the zigzag transition is presented, which predicts correctly the behavior of this transition from which we interpret the structural phase transition of the Wigner crystal through the reduction of the Brillouin zone.Comment: 9 pages, 13 figure

Exotic phase diagram of a topological quantum system

We study the quantum phase transitions (QPTs) in the Kitaev spin model on a triangle-honeycomb lattice. In addition to the ordinary topological QPTs between Abelian and non-Abelian phases, we find new QPTs which can occur between two phases belonging to the same topological class, namely, either two non-Abelian phases with the same Chern number or two Abelian phases with the same Chern number. Such QPTs result from the singular behaviors of the nonlocal spin-spin correlation functions at the critical points.Comment: 10 pages, 5 figure

Thermodynamics of ferromagnetic superconductors with spin-triplet electron pairing

We present a general thermodynamic theory that describes phases and phase transitions of ferromagnetic superconductors with spin-triplet electron Cooper pairing. The theory is based on extended Ginzburg-Landau expansion in powers of superconducting and ferromagnetic order parameters. We propose a simple form for the dependence of theory parameters on the pressure that allows correct theoretical outline of the temperature-pressure phase diagram for which at low temperatures a stable phase of coexistence of p-wave superconductivity and itinerant ferromagnetism appears. We demonstrate that the theory is in an agreement with the experimental data for some intermetallic compounds that are experimentally proven to be itinerant ferromagnetic exhibiting spin-triplet superconductivity. Some basic features of quantum phase transitions in such systems are explained and clarified. We propose to group the spin-triplet ferromagnetic superconductors in two different types of thermodynamic behavior, on the basis of quantitative criterion deduced from the present theory and the analysis of experimental data.Comment: Phys. Rev. B (2009) in PRESS; 14 pages, 1 table, 6 figures, Latex2