503 research outputs found
Radiation Due to Josephson Oscillations in Layered Superconductors
We derive the power of direct radiation into free space induced by Josephson
oscillations in intrinsic Josephson junctions of highly anisotropic layered
superconductors. We consider the super-radiation regime for a crystal cut in
the form of a thin slice parallel to the c-axis. We find that the radiation
correction to the current-voltage characteristic in this regime depends only on
crystal shape. We show that at large enough number of junctions oscillations
are synchronized providing high radiation power and efficiency in the THz
frequency range. We discuss crystal parameters and bias current optimal for
radiation power and crystal cooling.Comment: 4 pages, 1 figure, to be published in Phys. Rev. Let
Inhomogeneous LOFF phase revisited for surface superconductivity
We consider 2D surface superconductivity in high magnetic fields parallel to
the surface. We demonstrate that the spin-orbit interaction at the surface
changes the properties of the inhomogeneous superconducting
Larkin-Ovchinnikov-Fulde-Ferrell state that develops above fields given by the
paramagnetic criterion. Strong spin-orbit interaction significantly broadens
the range of existence of the LOFF phase, which takes the form of periodic
superconducting stripes running along the field direction on the surface,
leading to the anisotropy of its properties. In connection with experiments by
J.H. Schon et al. [Nature 914, 434 (2001)] on superconductivity of electrically
doped films of the cuprate material CaCuO2, we also discuss this problem for
the d-wave pairing to indicate the possibility of a re-orientation transition
as the magnetic field direction is rotated in the plane parallel to the
surface. Our results provide a tool for studying surface superconductivity as a
function of doping.Comment: 4 pages, 1 fig, revtex
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
Dissociation Transition of a Composite Lattice of Magnetic Vortices in the Flux-Flow Regime of Two-Band Superconductors
In multiband superconductors, each superconducting condensate supports
vortices with fractional quantum flux. In the ground state, vortices in
different bands are spatially bounded together to form a composite vortex,
carrying one quantum flux \Phi_0. Here we predict dissociation of the composite
vortices lattice in the flux flow state due to the disparity of the vortex
viscosity and flux of the vortex in different bands. For a small driving
current, composite vortices start to deform, but the constituting vortices in
different bands move with the same velocity. For a large current, composite
vortices dissociate and vortices in different bands move with different
velocities. The dissociation transition shows up as an increase of flux flow
resistivity. In the dissociated phase, Shapiro steps are developed when an ac
current is superimposed with a dc current.Comment: 4.5 pages, 3 figure
Ferromagnetic Film on a Superconducting Substrate
We study the equilibrium domain structure and magnetic flux around a
ferromagnetic (FM) film with perpendicular magnetization M_0 on a
superconducting (SC) substrate. At 4{\pi}M_0<H_{c1} the SC is in the Meissner
state and the equilibrium domain width in the film, l, scales as
(l/4{\pi}{\lambda}_{L}) = (l_{N}/4{\pi}{\lambda}_{L})^{2/3} with the domain
width on a normal (non-superconducting) substrate, l_{N}/4\pi\lambda_L >> 1.
Here \lambda_L is the London penetration length. For 4{\pi}M_0 > H_{c1} and
l_{N} in excess of about 35 {\lambda}_{L}, the domains are connected by SC
vortices. We argue that pinning of vortices by magnetic domains in FM/SC
multilayers can provide high critical currents.Comment: 4 pages, 2 figures, submitted to PR
Electronic Orbital Currents and Polarization in Mott Insulators
The standard view is that at low energies Mott insulators exhibit only
magnetic properties while charge degrees of freedom are frozen out as the
electrons become localized by a strong Coulomb repulsion. We demonstrate that
this is in general not true: for certain spin textures {\it spontaneous
circular electric currents} or {\it nonuniform charge distribution} exist in
the ground state of Mott insulators. In addition, low-energy ``magnetic''
states contribute comparably to the dielectric and magnetic functions
and leading to interesting phenomena
such as rotation the electric field polarization and resonances which may be
common for both functions producing a negative refraction index in a window of
frequencies
Interaction of a Nanomagnet with a Weak Superconducting Link
We study electromagnetic interaction of a nanomagnet with a weak
superconducting link. Equations that govern coupled dynamics of the two systems
are derived and investigated numerically. We show that the presence of a small
magnet in the proximity of a weak link may be detected through Shapiro-like
steps caused by the precession of the magnetic moment. Despite very weak
magnetic field generated by the weak link, a time-dependent bias voltage
applied to the link can initiate a non-linear dynamics of the nanomagnet that
leads to the reversal of its magnetic moment. We also consider quantum problem
in which a nanomagnet interacting with a weak link is treated as a two-state
spin system due to quantum tunneling between spin-up and spin-down states.Comment: 7 pages, 4 figure
Fine structure of the local pseudogap and Fano effect for superconducting electrons near a zigzag graphene edge
Motivated by recent scanning tunneling experiments on zigzag-terminated
graphene this paper investigates an interplay of evanescent and extended
quasiparticle states in the local density of states (LDOS) near a zigzag edge
using the Green's function of the Dirac equation. A model system is considered
where the local electronic structure near the edge influences transport of both
normal and superconducting electrons via a Fano resonance. In particular, the
temperature enhancement of the critical Josephson current and 0-pi transitions
are predicted.Comment: 5 pages, 5 figures, to be published in Phys. Rev.
Spin-precession-assisted supercurrent in a superconducting quantum point contact coupled to a single-molecule magnet
The supercurrent of a quantum point contact coupled to a nanomagnet strongly
depends on the dynamics of the nanomagnet's spin. We employ a fully microscopic
model to calculate the transport properties of a junction coupled to a spin
whose dynamics is modeled as Larmor precession brought about by an external
magnetic field and find that the dynamics affects the charge and spin currents
by inducing transitions between the continuum states below the superconducting
gap edge and the Andreev levels. This redistribution of the quasiparticles
leads to a non-equilibrium population of the Andreev levels and an enhancement
of the supercurrent which is visible as a modified current-phase relation as
well as a non-monotonous critical current as function of temperature. The
non-monotonous behavior is accompanied by a corresponding change in
spin-transfer torques acting on the precessing spin and leads to the
possibility of using temperature as a means to tune the back-action on the
spin.Comment: 11 pages, 5 figure
Josephson effect in thin-film superconductor/insulator/superconductor junctions with misaligned in-plane magnetic fields
We study a tunnel junction consisting of two thin-film s-wave superconductors
separated by a thin, insulating barrier in the presence of misaligned in-plane
exchange fields. We find an interesting interplay between the superconducting
phase difference and the relative orientation of the exchange fields,
manifested in the Josephson current across the junction. Specifically, this may
be written , where
I_0 and I_m are constants, and is the relative orientation of the
exchange fields while is the superconducting phase difference.
Similar results have recently been obtained in other S/I/S junctions coexisting
with helimagnetic or ferromagnetic order. We calculate the superconducting
order parameter self-consistently, and investigate quantitatively the effect
which the misaligned exchange fields constitute on the Josephson current, to
see if I_m may have an appreciable effect on the Josephson current. It is found
that I_0 and I_m become comparable in magnitude at sufficiently low
temperatures and fields close to the critical value, in agreement with previous
work. From our analytical results, it then follows that the Josephson current
in the present system may be controlled in a well-defined manner by a rotation
of the exchange fields on both sides of the junction. We discuss a possible
experimental realization of this proposition.Comment: 8 pages, 8 figures. Accepted for publication in Phys. Rev.
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