Josephson junctions with negative second harmonic in the current-phase relation: properties of novel varphi-junctions

Several recent experiments revealed a change of the sign of the first harmonic in the current-phase relation of Josephson junctions (JJ) based on novel superconductors, e.g., d-wave based or JJ with ferromagnetic barrier. In this situation the role of the second harmonic becomes dominant and it determines the scenario of a 0-pi transition. We discuss different mechanisms of the second harmonic generation and its sign. If the second harmonic is negative the 0-pi transition becomes continuous and the realization of the so-called varphi junction is possible. We study the unusual properties of such a novel JJ and analyze the possible experimental techniques for their observation.Comment: submitted to PR

Dephasing time of disordered two-dimensional electron gas in modulated magnetic fields

The dephasing time of disordered two-dimensional electron gas in a modulated magnetic field is studied. It is shown that in the weak inhomogeneity limit, the dephasing rate is proportional to the field amplitude, while in strong inhomogeneity limit the dependence is quadratic. It is demonstrated that the origin of the dependence of dephasing time on field amplitude lies in the nature of corresponding single-particle motion. A semiclassical Monte Carlo algorithm is developed to study the dephasing time, which is of qualitative nature but efficient in uncovering the dependence of dephasing time on field amplitude for arbitrarily complicated magnetic-field modulation. Computer simulations support analytical results. The crossover from linear to quadratic dependence is then generalized to the situation with magnetic field modulated periodically in one direction with zero mean, and it is argued that this crossover can be expected for a large class of modulated magnetic fields.Comment: 8 pages, 2 figure

Erratum - Modulated smectic C*-uniform smectic C* phase transition in an electric field

No abstract availabl

Modulated smectic C*-uniform smectic C* phase transition in an electric field

A detailed analytic description of the phase transition in an electric field between the modulated smectic C chiral phase and the uniform smectic C chiral phase is given taking into account both ferroelectric and dielectric coupling to the field in the case of negative anisotropy. Within the Landau theory of phase transitions we find helix distortions, and establish the field dependence of the pitch and the phase boundaries in the E-T phase diagram. The transition considered here is continuous. The evolution of the polarization and susceptibility with the field is described as well as domain walls in the uniform phase. The fluctuation spectrum for some values of the field also contains, besides the usual phason and phonon branches, a new oscillatory branch. The disappearance of the walls occurs through unwinding in our model but we also suggest a possible mechanism through line defects.La transition de phase entre le smectique C chiral uniforme et le smectique C chiral modulé est étudiée analytiquement en prenant en compte le couplage ferroélectrique et diélectrique pour un smectique caractérisé par une anisotropie négative. Dans le cadre de la théorie de Landau on a trouvé les distorsions de la structure hélicoïdale, la dépendance du pas de l'hélice par rapport au champ électrique, ainsi que les domaines d'existence des différentes phases dans le diagramme E-T. La transition considérée est continue. On décrit l'évolution avec le champ de la polarisation et de la susceptibilité de même que celle des parois dans la phase uniforme. Dans le spectre des fluctuations on a trouvé non seulement les branches du phason et du phonon, mais aussi une nouvelle branche d'oscillations. Pour décrire la disparition des parois on a proposé soit le mécanisme de déroulement de la structure hélicoïdale, soit un processus de disparition à l'aide de défauts linéaires