Topological Structure of a Vortex in Fulde-Ferrell-Larkin-Ovchinnikov State

We find theoretically that the vortex core in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is quite different from the ordinary core by a simple topological reason. The intersection point of a vortex and nodal plane of the FFLO state empties the excess spins. This leads to observable consequences in the spatial structure of the spontaneous magnetization. We analyze this topological structure based on the low lying excitation spectrum by solving microscopic Bogoliubov-de Gennes equation to clarify its physical origin.Comment: 4 pages, 4 figure

Majorana bound state in rotating superfluid 3He-A between parallel plates

A concrete and experimentally feasible example for testing the putative Majorana zero energy state bound in a vortex is theoretically proposed for a parallel plate geometry of superfluid $^3$He-A phase. We examine the experimental setup in connection with ongoing rotating cryostat experiments. The theoretical analysis is based on the well-established Ginzburg--Landau functional, supplemented by microscopic calculations of the Bogoliubov--de Gennes equation, both of which allow the precise location of the parameter regions of the Majorana state to be found in realistic situations.Comment: 5 pages, 4 figure

Electronic state around vortex in a two-band superconductor

Based on the quasiclassical theory, we investigate the vortex state in a two-band superconductor with a small gap on a three dimensional Fermi surface and a large gap on a quasi-two dimensional one, as in MgB_2. The field dependence of zero-energy density of states is compared for fields parallel and perpendicular to the ab plane, and the anisotropy of the vortex core shape is discussed for a parallel field. The Fermi surface geometry of two-bands, combining the effect of the normal-like electronic state on the small gap band at high fields, produces characteristic behavior in the anisotropy of c- and ab-directions.Comment: 6 pages, 6 figures, to appear in Phys. Rev.

Vortex Structure in Superconducting Stripe States

The vortex structure in superconducting stripe states is studied according to the Bogoliubov-de Gennes theory on the two-dimensional Hubbard model with nearest-neighbor sites pairing interaction. The vortex is trapped at the outside region of the stripe line, where the superconductivity is weak. The superconducting coherence length along the stripe direction becomes long. There are no eminent low-energy electronic states even near the vortex core. These characters resemble the Josephson vortex in layered superconductors under a parallel field.Comment: LaTeX 5 pages (using jpsj macros) with 3 figure

Field dependence of the vortex structure in chiral p-wave superconductors

To investigate the different vortex structure between two chiral pairing p_x +(-) i p_y, we calculate the pair potential, the internal field, the local density of states, and free energy in the vortex lattice state based on the quasiclassical Eilenberger theory, and analyze the magnetic field dependence. The induced opposite chiral component of the pair potential plays an important role in the vortex structure. It also produces H^{1/2}-behavior of the zero-energy density of states at higher field. These results are helpful when we understand the vortex states in Sr2RuO4.Comment: 11 pages, 10 figures, to be published in Phys. Rev.

Generic Phase Diagram of Fermion Superfluids with Population Imbalance

It is shown by microscopic calculations for trapped imbalanced Fermi superfluids that the gap function has always sign changes, i.e., the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state like, up to a critical imbalance $P_c$, beyond which normal state becomes stable, at temperature T=0. A phase diagram is constructed in $T$ vs $P$, where the BCS state without sign change is stable only at $T\neq 0$. We reproduce the observed bimodality in the density profile to identify its origin and evaluate $P_c$ as functions of $T$ and the coupling strength. These dependencies match with the recent experiments.Comment: 5 pages, 5 figures, replaced by the version to appear in PR

Vortex state in double transition superconductors

Novel vortex phase and nature of double transition field are investigated by two-component Ginzburg-Landau theory in a situation where fourfold-twofold symmetric superconducting double transition occurs. The deformation from 60 degree triangular vortex lattice and a possibility of the vortex sheet structure are discussed. In the presence of the gradient coupling, the transition changes to a crossover at finite fields. These characters are important to identify the multiple superconducting phase in PrOs_4_Sb_12.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Direct Imaging of Spatially Modulated Superfluid Phases in Atomic Fermion Systems

It is proposed that the spatially modulated superfluid phase, or the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state could be observed in resonant Fermion atomic condensates which are realized recently. We examine optimal experimental setups to achieve it by solving Bogoliubov-de Gennes equation both for idealized one-dimensional and realistic three-dimensional cases. The spontaneous modulation of this superfluid is shown to be directly imaged as the density profiles either by optical absorption or by Stern-Gerlach experiments.Comment: 4 pages, 3 figure

Induced Kramer-Pesch-Effect in a Two Gap Superconductor: Application to MgB2

The size of the vortex core in a clean superconductor is strongly temperature dependent and shrinks with decreasing temperature, decreasing to zero for T -> 0. We study this so-called Kramer-Pesch effect both for a single gap superconductor and for the case of a two gap superconductor using parameters appropriate for Magnesium Diboride. Usually, the Kramer-Pesch effect is absent in the dirty limit. Here, we show that the Kramer-Pesch effect exists in both bands of a two gap superconductor even if only one of the two bands is in the clean limit and the other band in the dirty limit, a case appropriate for MgB2. In this case an induced Kramer-Pesch effect appears in the dirty band. Besides numerical results we also present an analytical model for the spatial variation of the pairing potential in the vicinity of the vortex center that allows a simple calculation of the vortex core radius even in the limit T -> 0.Comment: 12 pages, 12 figure

Sign reversal of field-angle resolved heat capacity oscillations in a heavy fermion superconductor CeCoIn5_5 and dx2−y2d_{x^2-y^2} pairing symmetry

To identify the superconducting gap symmetry in CeCoIn5 (Tc=2.3 K), we performed angle-resolved specific heat (C_\phi) measurements in a field rotated around the c-axis down to very low temperatures 0.05Tc and detailed theoretical calculations. In a field of 1 T, a sign reversal of the fourfold angular oscillation in C_\phi has been observed at T ~ 0.1Tc on entering a quasiclassical regime where the maximum of C_\phi corresponds to the antinodal direction, coinciding with the angle-resolved density of states (ADOS) calculation. The C_\phi behavior, which exhibits minima along [110] directions, unambiguously allows us to conclude d_{x^2-y^2} symmetry of this system. The ADOS-quasiclassical region is confined to a narrow T and H domain within T/Tc ~ 0.1 and 1.5 T (0.13Hc2).Comment: 4 pages, 4 figure