Magnetic order in Ce0.95Nd0.05CoIn5: the Q-phase at zero magnetic field

We report neutron scattering experiment results revealing the nature of the magnetic order occurring in the heavy fermion superconductor Ce0.95Nd0.05CoIn5, a case for which an antiferromagnetic state is stabilized at a temperature below the superconducting transition one. We evidence an incommensurate order and its propagation vector is found to be identical to that of the magnetic field induced antiferromagnetic order occurring in the stoichiometric superconductor CeCoIn5, the so-called Q-phase. The commonality between these two cases suggests that superconductivity is a requirement for the formation of this kind of magnetic order and the proposed mechanism is the enhancement of nesting condition by d-wave order parameter with nodes in the nesting area.Comment: submitted to Phys. Rev. Lett. on June 30th, 201

Dynamics of the penetration boundaries of solar protons during a strong magnetic storm

The variations in the equatorial penetration boundary of solar protons with E sub p = 0.9 to 8.0 MeV during a strong magnetic storm of April 3 to 5, were analyzed. The dynamics of this boundary is compared with the dynamics of the outer trapping boundary of electrons with E sub e = - 0.3 to 0.6 MeV. The solar-proton penetration and the structure of the real magnetic field are studied. The unique data on the thin structure of development of a magnetospheric substorm were obtained for the first time

Surface Melting of the Vortex Lattice in Layered Superconductors: Density Functional Theory

We study the effects of an $ab$-surface on the vortex-solid to vortex-liquid transition in layered superconductors in the limit of vanishing inter-layer Josephson coupling. We derive the interaction between pancake vortices in a semi-infinite sample and adapt the density functional theory of freezing to this system. We obtain an effective one-component order-parameter theory which can be used to describe the effects of the surface on vortex-lattice melting. Due to the absence of protecting layers in the neighbourhood of the surface, the vortex lattice formed near the surface is more susceptible to thermal fluctuations. Depending on the value of the magnetic field, we predict either a continuous or a discontinuous surface melting transition. For intermediate values of the magnetic field, the surface melts continuously, assisting the formation of the liquid phase and suppressing hysteresis above the melting transition, a prediction consistent with experimental results. For very low and very high magnetic fields, the surface melts discontinuously. The two different surface melting scenarios are separated by two surface multicritical points, which we locate on the melting line.Comment: 16 pages, 12 figure

Fractional-flux vortices and spin superfluidity in triplet superconductors

We discuss a novel type of fractional flux vortices along with integer flux vortices in Kosterlitz-Thouless transitions in a triplet superconductor. We show that under certain conditions a spin-triplet superconductor should exhibit a novel state of {\it spin superfluidity} without superconductivity.Comment: Physical Review Lettes, in print. v2: references added, v3: discussion of several points extended according to referee request. Latest updates and links to related papers are available at my homepage http://people.ccmr.cornell.edu/~egor

Recent developments in unconventional superconductivity theory

The review of recent developments in the unconventional superconductivity theory is given. In the fist part I consider the physical origin of the Kerr rotation polarization of light reflected from the surface of superconducting $Sr_2RuO_4$. Then the comparison of magneto-optical responses in superconductors with orbital and spin spontaneous magnetization is presented. The latter result is applied to the estimation of the magneto-optical properties of neutral superfluids with spontaneous magnetization. The second part is devoted to the natural optical activity or gyrotropy properties of noncentrosymmetric metals in their normal and superconducting states. The temperature behavior of the gyrotropy coefficient is compared with the temperature behavior of paramagnetic susceptibility determining the noticeable increase of the paramagnetic limiting field in noncentrosymmetric superconductors. In the last chapter I describe the order parameter and the symmetry of superconducting state in the itinerant ferromagnet with orthorhombic symmetry. Finally the Josephson coupling between two adjacent ferromagnet superconducting domains is discussed.Comment: 15 page

The ground state of binary systems with a periodic modulation of the linear coupling

We consider a quasi-one-dimensional two-component systm, described by a pair of Nonlinear Schr\"{o}dinger/Gross-Pitaevskii Equations (NLSEs/GPEs), which are coupled by the linear mixing, with local strength $\Omega$, and by the nonlinear incoherent interaction. We assume the self-repulsive nonlinearity in both components, and include effects of a harmonic trapping potential. The model may be realized in terms of periodically modulated slab waveguides in nonlinear optics, and in Bose-Einstein condensates too. Depending on the strengths of the linear and nonlinear couplings between the components, the ground states (GSs) in such binary systems may be symmetric or asymmetric. In this work, we introduce a periodic spatial modulation of the linear coupling, making $\Omega$ an odd, or even function of the coordinate. The sign flips of $\Omega (x)$ strongly modify the structure of the GS in the binary system, as the relative sign of its components tends to lock to the local sign of $\Omega$. Using a systematic numerical analysis, and an analytical approximation, we demonstrate that the GS of the trapped system contains one or several kinks (dark solitons) in one component, while the other component does not change its sign. Final results are presented in the form of maps showing the number of kinks in the GS as a function of the system's parameters, with the odd/even modulation function giving rise to the odd/even number of the kinks. The modulation of $\Omega (x)$ also produces a strong effect on the transition between states with nearly equal and strongly unequal amplitudes of the two components.Comment: 8 pages, 3 figure

Classical phase fluctuations in d-wave superconductors

We study the effects of low-energy nodal quasiparticles on the classical phase fluctuations in a two-dimensional d-wave superconductor. The singularities of the phase-only action at T\to 0 are removed in the presence of disorder, which justifies using an extended classical XY-model to describe phase fluctuations at low temperatures.Comment: 14 pages, brief review for Mod. Phys. Lett.

Paired electron pockets in the hole-doped cuprates

We propose a theory for the underdoped hole-doped cuprates, focusing on the "nodal-anti-nodal dichotomy" observed in recent experiments. Our theory begins with an ordered antiferromagnetic Fermi liquid with electron and hole pockets. We argue that it is useful to consider a quantum transition at which the loss of antiferromagnetic order leads to a hypothetical metallic "algebraic charge liquid" (ACL) with pockets of charge -e and +e fermions, and an emergent U(1) gauge field; the instabilities of the ACL lead to the low temperature phases of the underdoped cuprates. The pairing instability leads to a superconductor with the strongest pairing within the -e Fermi pockets, a d-wave pairing signature for electrons, and very weak nodal-point pairing of the +e fermions near the Brillouin zone diagonals. The influence of an applied magnetic field is discussed using a proposed phase diagram as a function of field strength and doping. We describe the influence of gauge field and pairing fluctuations on the quantum Shubnikov-de Haas oscillations in the normal states induced by the field. For the finite temperature pseudogap region, our theory has some similarities to the phenomenological two-fluid model of -2e bosons and +e fermions proposed by Geshkenbein, Ioffe, and Larkin [cond-mat/9609209], which describes anomalous aspects of transverse transport in a magnetic field.Comment: 38 pages, 5 figures; (v3) added refs and shortened Section IV; (v4) added phase diagram

Roton dipole moment

The roton excitation in the superfluid He-4 does not possess a stationary dipole moment. However, a roton has an instantaneous dipole moment, such that at any given moment one can find it in the state either with positive or with negative dipole moment projection on its momentum direction. The instantaneous value of electric dipole moment of roton excitation is evaluated. The result is in reasonable agreement with recent experimental observation of the splitting of microwave resonance absorption line at roton frequency under external electric field.Comment: 5 page