Search results for "conductivity"
showing 10 items of 1988 documents
ac conductivity inLa2CuO4
1992
Measurements of the complex ac conductivity are reported for a single crystal of ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ for frequencies ${10}^{2}$\ensuremath{\le}\ensuremath{\nu}\ensuremath{\le}${10}^{9}$ Hz and temperatures 25\ensuremath{\le}T\ensuremath{\le}300 K. The conductivity follows a power-law behavior ${\mathrm{\ensuremath{\omega}}}^{\mathit{s}}$ with the frequency exponent s independent of temperature and independent of frequency. However, the hopping transport is strongly anisotropic, with s\ensuremath{\approxeq}0.75 within the ${\mathrm{CuO}}_{2}$ planes and s\ensuremath{\approxeq}0.25 perpendicular to the planes.
Magnetoelectric effects in superconductors due to spin-orbit scattering : Nonlinear σ-model description
2021
We suggest a generalization of the nonlinear σ model for diffusive superconducting systems to account for magnetoelectric effects due to spin-orbit scattering. In the leading orders of spin-orbit strength and gradient expansion, it includes two additional terms responsible for the spin-Hall effect and the spin-current swapping. First, assuming a delta-correlated disorder, we derive the terms from the Keldysh path integral representation of the generating functional. Then we argue phenomenologically that they exhaust all invariants allowed in the effective action to the leading order in the spin-orbit coupling (SOC). Finally, the results are confirmed by a direct derivation of the saddle-poi…
Fractal dimension of superfluid turbulence : A random-walk toy model
2021
This paper deals with the fractal dimension of a superfluid vortex tangle. It extends a previous model [J. Phys. A: Math. Theor. {\bf 43}, 205501 (2010)] (which was proposed for very low temperature), and it proposes an alternative random walk toy model, which is valid also for finite temperature. This random walk model combines a recent Nemirovskii's proposal, and a simple modelization of a self-similar structure of vortex loops (mimicking the geometry of the loops of several sizes which compose the tangle). The fractal dimension of the vortex tangle is then related to the exponents describing how the vortex energy per unit length changes with the length scales, for which we take recent pr…
Transport Properties of Correlated Electrons in High Dimensions
2003
We develop a new general algorithm for finding a regular tight-binding lattice Hamiltonian in infinite dimensions for an arbitrary given shape of the density of states (DOS). The availability of such an algorithm is essential for the investigation of broken-symmetry phases of interacting electron systems and for the computation of transport properties within the dynamical mean-field theory (DMFT). The algorithm enables us to calculate the optical conductivity fully consistently on a regular lattice, e.g., for the semi-elliptical (Bethe) DOS. We discuss the relevant f-sum rule and present numerical results obtained using quantum Monte Carlo techniques.
Mixing of Two-Quasiparticle Configurations
2007
In this chapter we discuss configuration mixing of two-quasiparticle states. It is caused by the residual interaction remaining beyond the quasiparticle mean field defined in Chap. 13. We derive the equations of motion by the EOM method developed in Sect. 11.1. To accomplish this we need to express the residual Hamiltonian in terms of quasiparticles.
Transverse distribution of beam current oscillations of a 14 GHz electron cyclotron resonance ion source
2014
The temporal stability of oxygen ion beams has been studied with the 14 GHz A-ECR at JYFL (University of Jyvaskyla, Department of Physics). A sector Faraday cup was employed to measure the distribution of the beam current oscillations across the beam profile. The spatial and temporal characteristics of two different oscillation “modes” often observed with the JYFL 14 GHz ECRIS are discussed. It was observed that the low frequency oscillations below 200 Hz are distributed almost uniformly. In the high frequency oscillation “mode,” with frequencies >300 Hz at the core of the beam, carrying most of the current, oscillates with smaller amplitude than the peripheral parts of the beam. The result…
Bistability and “Negative” Viscosity for a Suspension of Insulating Particles in an Electric Field
2003
It is shown that a suspension of insulating particles in a liquid with low conductivity possesses bistability and has a "negative" effective viscosity effect in the electric field due to internal rotations. By Brownian dynamics simulation it has been found that thermal fluctuations of the angular velocity of particles in this bistable system can have a large effect on the viscosity of the suspension.
M4_Microfluidics_for_CNT
2018
Size and frequency of the droplets produced in T-junction as a function of continuous and disperse phase pressure ratio.
Membrane potential of rat calvaria bone cells: dependence on temperature.
1990
The membrane potentials of bone cells derived from calvaria of new born rats was shown to be strongly dependent on temperature. When we lowered the temperature from 36 degrees C to 26 degrees C, cells with spontaneous resting membrane potentials (MP) of -80 to -50 mV depolarized (mean amplitude 8 mV; n = 33), and the membrane resistance increased by approximately 80% (n = 20). The temperature response depended on the actual MP, the reversal potential being in the range of -80 to -90 mV. With the application of ouabain (0.1-1 mmol/liter; n = 12), cells depolarized. Simultaneously, the reversal potential of the temperature response was shifted towards more positive values and approached the a…
Josephson junctions and SQUIDs based on artificial grain boundaries in Bi 2 Sr 2 Ca 2 Cu 3 O 10 -thin films
1996
ABSTRACT High quality thin films of Bi2 Sr Ca2 Cu3 0 with critical temperatures of 95 K were used to prepare grainboundary josephson junctions on commercial 36.8° SrTiOg-bicrystal substrates. IR-products of 50 pV at 77 Kand 0.7 mV at 4.2 K have been reached. For temperatures higher than 50 K the current-voltage curves of thejunctions can be well described by the resistively shunted junction (RSJ) model and show no hysteresis. Fromthe hysteretic behavior at low temperature we estimate a junction capacitance of 2ljiF/cm2. The Fraunhoferpattern of the critical current in an external applied field shows, that the junctions are inhomogeneous on a pm scale. The SQUID modulation of a 30 x 40 pm2 w…