261 research outputs found
Observation of two species of vortices in the anisotropic spin-triplet superconductor
Magnetic flux structures in single crystals of the layered spin triplet
superconductor SrRuO are studied by scanning micro SQUID Force
microscopy. Vortex chains appear as the applied field is tilted along the
in-plane direction of the superconductor. The vortex chains align along the
direction of the in-plane component of the applied magnetic field. The
decoration of in-plane vortices by crossing Abrikosov vortices is observed: two
vortex orientations are apparent simultaneously, one along the layers and the
other perpendicular to the layers. The crossing vortices appear preferentially
on the in-plane vortices
The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/d-wave superconductor contact
The influence of phase shifts of electron waves passing through and reflected
by the potential barrier on the Andreev reflection in a
ferromagnet/isolator/d-wave superconductor (FIS) contact is studied. It is
found that in a superconductor the surface spin-dependent Andreev bound states
inside the superconducting gap are formed as a result of the interference of
electron-like and hole-like quasiparticles due to repeated Andreev reflections.
The peak in the conductance of the FIS contact at the zero potential for the
(110)-oriented superconductor disappears rapidly as the polarization of a
ferromagnet increases, whereas for the (100)-oriented superconductor it
appears. The physical reason for this behavior of conductance is discussed.Comment: 8 pages, 4 figure
Reply to "Comment on "Domain Structure in a Superconducting Ferromagnet""
This short article is a reply to the comment from E.B. Sonin on our paper on
the domain structure in a superconducting ferromagnet published in Phys. Rev.
Lett..Comment: 1 page, accepted for publication in Phys. Rev. Let
Observation of vortex coalescence in the anisotropic spin-triplet superconductor SrRuO
We present direct imaging of magnetic flux structures in the anisotropic,
spin-triplet superconductor SrRuO using a scanning SQUID
microscope. Individual quantized vortices were seen at low magnetic fields.
Coalescing vortices forming flux domains were revealed at intermediate fields.
Based on our observations we suggest that a mechanism intrinsic to the material
stabilizes the flux domains against the repulsive vortex-vortex interaction.
Topological defects like domain walls can provide this, implying proof for
unconventional chiral superconductivity.Comment: submitted to PR
FFLO state in thin superconducting films
We present the analysis of the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) superconducting state in thin superconducting films in the parallel
magnetic field. For the tetragonal crystal symmetry (relevant to CeCoIn -
the most probable candidate for the FFLO state formation) we predict a very
peculiar in-plane angular dependence of the FFLO critical field due to the
orbital effect. In the uniform superconducting state the critical field should
be isotropic. The magnetic field pins also the direction of the FFLO modulation
permitting thus to study the critical current anisotropy. Our calculations
reveal a strong critical current anisotropy in the FFLO state in sharp contrast
with the usual superconducting state. The predicted characteristic anisotropies
of the critical field and critical current may provide an unambiguous probe of
the FFLO phase formation.Comment: 7 pages, 2 figures, to be published in Europhys. Let
Little-Parks Oscillations in Hybrid Ferromagnet-Superconductor Systems
On the basis of of linearized Usadel equations we consider superconductivity
nucleation in multiply connected mesoscopic superconductor/ferromagnet hybrids
such as thin-walled superconducting cylinders placed in electrical contact with
a ferromagnetic metal. We study the interplay between the oscillations of
due to the Little--Parks effect and the oscillations due to the exchange field.
We demonstrate that the exchange field provokes the switching between the
superconducting states with different vorticities and this may result in the
increase the critical temperature of the superconducting transition in the
magnetic field. Moreover we analyse the influence of the S/F transparency on
the realisation of the states with higher vorticities.Comment: 7 pages, 4 figure
Superharmonic Josephson relation at 0-/-junction transition
Critical current was recently measured near the transition from 0 to
-contact in superconductor/ferromagnet/superconductor Josephson junctions.
Contrary to expectations, it does not vanish at the transition point. It shows
instead a tiny, though finite, minimum. The observation of fractional Shapiro
steps reenforces the idea that the vanishing of the main sinusoidal term in the
Josephson relation gives room to the next harmonics. Within quasiclassical
approach we calculate the Josephson relation taking into account magnetic
scattering. We find that the observed minimum is compatible with the value of
the second harmonics expected from the theory.Comment: 5 pages, 2 Figs, 1 Tabl
Theory of Interplay of Nuclear Magnetism and Superconductivity in AuIn2
The recently reported coexistence of a magnetic order, with the critical
temperature T_M=35 \mu*K, and superconductivity, with the critical temperature
T_S=207 m*K, in AuIn_2 is studied theoretically. It is shown that
superconducting (S) electrons and localized nuclear magnetic moments (LM's)
interact dominantly via the contact hyperfine (EX) interaction, giving rise to
a spiral (or domain-like) magnetic order in superconducting phase. The
electromagnetic interaction between LM's and S electrons is small compared to
the EX one giving minor contribution to the formation of the oscillatory
magnetic order. In clean samples (l>\xi_0) of AuIn the oscillatory magnetic
order should produce a line of nodes in the quasiparticle spectrum of S
electrons giving rise to the power law behavior. The critical field H_c(T=0) in
the coexistence phase is reduced by factor two with respect to its bare value.Comment: 4 pages with 2 PS figures, RevTeX, submitted to Physical Review B -
Rapid Communication
Bound states at the interface between antiferromagnets and superconductors
We present a detailed theoretical investigation of interfaces and junctions
involving itinerant antiferromagnets. By solving the Bogoliubov-de Gennes
equations with a tight-binding model on a square lattice, we study both the
self-consistent order parameter fields proximate to interfaces between
antiferromagnets (AF) and s-wave (sSC) or d-wave (dSC) superconductors, the
dispersion of quasiparticle subgap states at interfaces and interlayers, and
the local density of states (LDOS) as a function of distance from the
interface. In addition, we present the quasiclassical approach to interfaces
and junctions involving itinerant antiferromagnets developed in an earlier
paper. Analytical results are in excellent agreement with what we obtain
numerically. Strong effects of pair breaking in the presence of low-energy
interface Andreev states are found in particular for AF/sSC interfaces when
interface potentials are not too high. Potential barriers induce additional
extrema in the dispersive quasiparticle spectra with corresponding peaks in the
LDOS. Discrete quasiparticle dispersive levels in AF - normal metal (N) - AF
systems are found to strongly depend on the misorientation angle of the
magnetizations in the two antiferromagnets.Comment: 21 pp, 21 postscript figures, submitted to Phys. Rev.
Fulde-Ferrell-Larkin-Ovchinnikov states in one-dimensional spin-polarized ultracold atomic Fermi gases
We present a systematic study of quantum phases in a one-dimensional
spin-polarized Fermi gas. Three comparative theoretical methods are used to
explore the phase diagram at zero temperature: the mean-field theory with
either an order parameter in a single-plane-wave form or a self-consistently
determined order parameter using the Bogoliubov-de Gennes equations, as well as
the exact soluble Bethe ansatz method. We find that a spatially inhomogeneous
Fulde-Ferrell-Larkin-Ovchinnikov phase, which lies between the fully paired BCS
state and the fully polarized normal state, dominates most of the phase diagram
of a uniform gas. The phase transition from the BCS state to the
Fulde-Ferrell-Larkin-Ovchinnikov phase is of second order, and therefore there
are no phase separation states in one-dimensional homogeneous polarized gases.
This is in sharp contrast to the three-dimensional situation, where a phase
separation regime is predicted to occupy a very large space in the phase
diagram. We conjecture that the prediction of the dominance of the phase
separation phases in three dimension could be an artifact of the
non-self-consistent mean-field approximation, which is heavily used in the
study of three-dimensional polarized Fermi gases. We consider also the effect
of a harmonic trapping potential on the phase diagram, and find that in this
case the trap generally leads to phase separation, in accord with the
experimental observations for a trapped gas in three dimension. We finally
investigate the local fermionic density of states of the
Fulde-Ferrell-Larkin-Ovchinnikov ansatz. A two-energy-gap structure is shown
up, which could be used as an experimental probe of the
Fulde-Ferrell-Larkin-Ovchinnikov states.Comment: 22 papes, 19 figure
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