Non linear excess conductivity of Bi2_2Sr2_2Can−1_{n-1}Cun_nO2n+4+x_{2n+4+x} (n = 1,2), thin films

The suppression of excess conductivity with electric field is studied for Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4+x}$ ($n$ = 1, 2) thin films. A pulse-probe technique is used, which allows for an estimate of the sample temperature. The characteristic electric field for fluctuations suppression is found well below the expected value for all samples. For the $n=1$ material, a scaling of the excess conductivity with electric field and temperature is obtained, similar to the scaling under strong magnetic field

Magnetothermopower and Nernst effect in unconventional charge density waves

Recently we have shown that the striking angular dependent magnetoresistance in the low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 is consistently described in terms of unconventional charge density wave (UCDW). Here we investigate theoretically the thermoelectric power and the Nernst effect in UDW. The present results account consistently for the recent data of magnetothermopower in alpha-(BEDT-TTF)_2KHg(SCN)_4 obtained by Choi et al. (Phys. Rev. B, 65, 205119 (2002)). This confirms further our identification of LTP in this salt as UCDW. We propose also that the Nernst effect provides a clear signature of UDW.Comment: 4 pages, 4 figure

Superconducting fluctuation corrections to ultrasound attenuation in layered superconductors

We consider the temperature dependence of the sound attenuation and sound velocity in layered impure metals due to superconducting fluctuations of the order parameter above the critical temperature. We obtain the dependence on material properties of these fluctuation corrections in the hydrodynamic limit, where the electron mean free path is much smaller than the wavelength of sound and where the electron collision rate is much larger than the sound frequency. For longitudinal sound propagating perpendicular to the layers, the open Fermi surface condition leads to a suppression of the divergent contributions to leading order, in contrast with the case of paraconductivity. The leading temperature dependent corrections, given by the Aslamazov-Larkin, Maki-Thompson and density of states terms, remain finite as T->Tc. Nevertheless, the sensitivity of new ultrasonic experiments on layered organic conductors should make these fluctuations effects measurable.Comment: 13 pages, 6 figures. Accepted for PRB. Added discussion on incoherent interlayer tunneling and other small modifications suggested by referee

Results of measurements of the analyzing powers for polarized neutrons on C, CH <inf>2</inf> and Cu targets for momenta between 3 and 4.2 GeV/c

The analyzing powers for neutron charge exchange nA → pX reactions on nuclei have been measured on C, CH2 and Cu targets at incident neutron momenta 3.0 - 4.2 GeV/c by detecting one charged particle in forward direction. The polarized neutron measurements are the first of their kind. The experiment was performed using the Nuclotron accelerator in JINR Dubna, where polarized neutrons and protons were obtained from breakup of a polarized deuteron beam which has a maximum momentum of 13 GeV/c. The polarimeter ALPOM2 was used to obtain the analyzing power dependence on the transverse momentum of the final-state nucleon. These data have been used to estimate the figure of merit of a proposed experiment at Jefferson Laboratory to measure the recoiling neutron polarization in the quasi-elastic 2H(e, e'n) reaction, which yields information on the charge and magnetic elastic form factors of the neutron

Introduction to the Special Issue “Professional Standard for Teachers”

Introduction to the Special Issue “Professional Standard for Teachers

In-plane and out-of-plane transport properties of Bi2Sr2CaCu2O8+delta epitaxial films: Fluctuations and transition into a vortex solid state

The in-plane (rho(ab)) and out-of-plane (rho(c)) resistivities of Bi2Sr2CaCu2O8+x films have been simultaneously measured in magnetic fields parallel to the films c axis (B less than or equal to 1 T). The rho(ab)(T,B) and rho(c)(T,B) curves are well described both above and below the zero-field critical temperature by the fluctuation theory in the Hartree approximation, using a single set of microscopic parameters for both directions. This agreement extends down to temperatures at which the dissipation is usually attributed to vortex motion. In the low-temperature region, however, both rho(ab) and p(c) exhibit a thermally activated behavior, and the I-V characteristics change from ohmic to nonohmic. We attribute this effect to the pinning-induced phase transition from a strongly fluctuating normal phase into a superconducting vortex solid phase

In-plane and out-of-plane transport properties of Bi2Sr2CaCu2O8+delta epitaxial films: Fluctuations and transition into a vortex solid state

The in-plane (rho(ab)) and out-of-plane (rho(c)) resistivities of Bi2Sr2CaCu2O8+x films have been simultaneously measured in magnetic fields parallel to the films c axis (B less than or equal to 1 T). The rho(ab)(T,B) and rho(c)(T,B) curves are well described both above and below the zero-field critical temperature by the fluctuation theory in the Hartree approximation, using a single set of microscopic parameters for both directions. This agreement extends down to temperatures at which the dissipation is usually attributed to vortex motion. In the low-temperature region, however, both rho(ab) and p(c) exhibit a thermally activated behavior, and the I-V characteristics change from ohmic to nonohmic. We attribute this effect to the pinning-induced phase transition from a strongly fluctuating normal phase into a superconducting vortex solid phase

The effect of fluctuations on thermomagnetic in high Tc superconductors - II

SIGLEITItal

The effect of fluctuations on the hall effect in high Tc superconductors - I

SIGLEITItal