543 research outputs found
Chemical potential of quasi-equilibrium magnon gas driven by pure spin current
We show experimentally that the spin current generated by the spin Hall
effect drives the magnon gas in a ferromagnet into a quasi-equilibrium state
that can be described by the Bose-Einstein statistics. The magnon population
function is characterized either by an increased effective chemical potential
or by a reduced effective temperature, depending on the spin current
polarization. In the former case, the chemical potential can closely approach,
at large driving currents, the lowest-energy magnon state, indicating the
possibility of spin current-driven Bose-Einstein condensation
Dynamical evolution of asteroid pairs with close orbits
Dynamical evolution of paired asteroids sharing close orbits was investigated. Candidates were chosen from AstDyS database by Kholshevnikov metric value. Only 33 of 105 pairs with close orbits were associated as family members. Further orbit evolution modeling was performed by Orbit9 software. Each pair had 49 overall model scenarios due to different Yarkovsky drift values for semimajor axis. Close encounters between paired objects providing time estimations and feasible mechanisms of formation were evaluated. Uncertainties of Yarkovsky drift values affected orbit evolution and caused substantial distinctions in time formation evaluating. Dwarf planet Ceres and massive asteroids (Pallas, Vesta, etc.) perturbations should be taken into account and dynamical evolution research for asteroid pairs in close orbits under passing through resonances is considered in future numerical simulations. © 2019 Author(s).The reported study was funded by RFBR according to the research project no. 18-02-00015
Nonlinear Seebeck Effect in a Model Granular Superconductor
The change of the Josephson supercurrent density of a weakly-connected
granular superconductor in response to externally applied arbitrary thermal
gradient dT/dx (nonlinear Seebeck effect) is considered within a model of 3D
Josephson junction arrays. For dT/dx>(dT/dx)_c, where (dT/dx)_c is estimated to
be of the order of 10^4 K/m for YBCO ceramics with an average grain's size of
10 microns, the weak-links-dominated thermopower S (Seebeck coefficient) is
predicted to become strongly dT/dx-dependent.Comment: REVTEX, no figure
Dynamics of An Underdamped Josephson Junction Ladder
We show analytically that the dynamical equations for an underdamped ladder
of coupled small Josephson junctions can be approximately reduced to the
discrete sine-Gordon equation. As numerical confirmation, we solve the coupled
Josephson equations for such a ladder in a magnetic field. We obtain
discrete-sine-Gordon-like IV characteristics, including a flux flow and a
``whirling'' regime at low and high currents, and voltage steps which represent
a lock-in between the vortex motion and linear ``phasons'', and which are
quantitatively predicted by a simple formula. At sufficiently high anisotropy,
the fluxons on the steps propagate ballistically.Comment: 11pages, latex, no figure
Optical Spin Orientation under Inter- and Intra-Subband Transitions in QWs
It is shown that absorption of circularly polarized infrared radiation
achieved by inter-subband and intra-subband (Drude-like) transitions results in
a monopolar spin orientation of free carriers. The monopolar spin polarization
in zinc-blende-based quantum wells (QWs) is demonstrated by the observation of
the spin-galvanic and circular photogalvanic effects. It is shown that
monopolar spin orientation in n-type QWs becomes possible if an admixture of
valence band states to the conduction band wave function and the spin-orbit
splitting of the valence band are taken into account
Dynamics and transformations of Josephson vortex lattice in layered superconductors
We consider dynamics of Josephson vortex lattice in layered superconductors
with magnetic, charge (electrostatic) and charge-imbalance (quasiparticle)
interactions between interlayer Josephson junctions taken into account. The
macroscopic dynamical equations for interlayer Josephson phase differences,
intralayer charge and electron-hole imbalance are obtained and used for
numerical simulations. Different transformations of the vortex lattice
structure are observed. It is shown that the additional dissipation due to the
charge imbalance relaxation leads to the stability of triangular lattice.Comment: 9 pages, 3 eps figures, to be published in Phys. Rev.
Aluminum Hard Mask Technique for the Fabrication of High-Quality Submicron Nb/Al-AlOx/Nb Josephson Junctions
We have developed a combined photolithography and electron-beam lithography
fabrication process for sub-\mum to \mum-size Nb/Al-AlOx/Nb Josephson
junctions. In order to define the junction size and protect its top electrode
during anodic oxidation, we developed and used the new concept of an aluminum
hard mask. Josephson junctions of sizes down to 0.5 \mum2 have been fabricated
and thoroughly characterized. We found that they have a very high quality,
which is witnessed by the IV curves with quality parameters Vm > 50 mV and Vgap
= 2.8 mV at 4.2 K, as well as IcRN products of 1.75-1.93 mV obtained at lower
temperatures. In order to test the usability of our fabrication process for
superconducting quantum bits, we have also designed, fabricated and
experimentally investigated phase qubits made of these junctions. We found a
relaxation time of T1 = 26 ns and a dephasing time of T2 = 21 ns
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