723 research outputs found
Strongly disordered Hubbard model in one dimension: spin and orbital infinite randomness and Griffiths phases
We study by the strong disorder renormalization group (RG) method the
low-energy properties of the one-dimensional Hubbard model with random-hopping
matrix-elements , and with random on-site Coulomb repulsion
terms . There are two critical phases, corresponding
to an infinite randomness spin random singlet for strong interactions () and to an orbital infinite randomness fixed point for vanishing
interactions (). To each critical infinite randomness
fixed point is connected a Griffiths phase, the correlation length and
dynamical exponent of which have well defined asymptotic dependences on the
corresponding quantum control parameter. The theoretical predictions for the
scaling in the vicinity of the critical points compare well to numerical RG
simulations.Comment: 9 pages, 7 figure
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
Nondemolition measurements of a single quantum spin using Josephson oscillations
We consider a Josephson junction containing a single localized spin 1/2
between conventional singlet superconducting electrodes. We study the spin
dynamics and measurements when a dc-magnetic field acts on
the spin and the junction is embedded into a dissipative circuit. We show that
when tunneling or a voltage are turned on at time the Josephson current
starts to oscillate with an amplitude depending on the initial () value of
the spin -component, . At low temperatures, when effects of
quasiparticles may be neglected, this procedure realizes a
quantum-non-demolition (QND) measurement of .Comment: 4 pages, 1 figure; average value of spin z operator changed to
eigenvalue S_
Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors
We consider the magnetic field dependence of the plasma resonance frequency
in pristine and in irradiated BiSrCaCuO crystals near . At
low magnetic fields we relate linear in field corrections to the plasma
frequency to the average distance between the pancake vortices in the
neighboring layers (wandering length). We calculate the wandering length in the
case of thermal wiggling of vortex lines, taking into account both Josephson
and magnetic interlayer coupling of pancakes. Analyzing experimental data, we
found that (i) the wandering length becomes comparable with the London
penetration depth near T and (ii) at small melting fields ( G) the
wandering length does not change much at the melting transition. This shows
existence of the line liquid phase in this field range. We also found that
pinning by columnar defects affects weakly the field dependence of the plasma
resonance frequency near .Comment: RevTex, 4 pages, 2 PS figures, Submitted to Phys. Rev.
Localized mode interactions in 0-pi Josephson junctions
A long Josephson junction containing regions with a phase shift of pi is
considered. By exploiting the defect modes due to the discontinuities present
in the system, it is shown that Josephson junctions with phase-shift can be an
ideal setting for studying localized mode interactions. A phase-shift
configuration acting as a double-well potential is considered and shown to
admit mode tunnelings between the wells. When the phase-shift configuration is
periodic, it is shown that localized excitations forming bright and dark
solitons can be created. Multi-mode approximations are derived confirming the
numerical results.Comment: 4 pages, to appear in Phys. Rev.
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
Current-phase relation in Josephson junction coupled with a magnetic dot
The current-phase relation (CPR) for a short Josephson junction placed in the
nonuniform field of a small ferromagnetic particle is studied. The effect of
the particle produced on the junction appears to be strong due to the formation
of the pair of oppositely directed Abrikosov vortices which pierce the thin
film superconducting electrode and cause a small--scale inhomogeneity of
Josephson phase difference. The induced phase difference inhomogeneity is shown
to result in the nonzero fixed phase drop across the junction. The
equilibrium value corresponding to the ground state of the junction
depends the configuration of the vortex--antivortex pair. The possibility to
tune the ground state phase difference is discussed.Comment: 6 pages, 5 figure
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