• Energy Research
• Physica B Condensed Matter close

Abstract Electrical resistivity of Y1−xPrxBa2Cu3Oy with x=0.45 has been measured around the superconducting transition temperature in applied magnetic fields. The superconducting transition becomes once broad above 1T and then narrowing of the transition appears in higher magnetic field above 9T for H∥c-axis. Furthermore, the pinning energy U0 of the vortex which is estimated from the temperature dependence of the resistivity in the low resistivity region of the transition behaves differently with respect to the magnetic field above and below 1T. These phenomena are discussed based on the temperature dependence of the depinning field, Hc2 and on pinning by the twin boundary.

Abstract The interaction between a small magnet and a high-temperature superconducting sphere in the field cooled state is investigated using the frozen image model. Analytical expression of the interaction potential and force between the magnet and the superconductor is derived as function of the geometrical parameters of the system. The angular dependence of the force and energy is analyzed. The interaction between a straight magnetic line and superconducting sphere is investigated.

By depositing ferromagnetic gratings on top of two-dimensional electron gases (2DEG), it is possible to generate periodic magnetic fields on a submicron scale in the plane of the electrons. Here, we show that the amplitude of the periodic magnetic field can be notably enhanced if the externally applied magnetic field B0 is tilted towards the plane of the 2DEG while kept normal to the gratings.

Abstract Galvanomagnetic effects in layered conductors with quasi-two-dimensional electron energy spectrum are studied theoretically. The magnitoresistance asymptote in high magnetic field H essentially depends on orientation of vector H. It is shown that in nonlinear conditions, the influence of the intrinsic magnetic field of stationary current on conduction electron ballistics leads to excitation of the voltage auto-oscillations.

Abstract In the inorganic spin-Peierls compound CuGeO3, we found a pronounced anisotropic magnetic energy dispersion, i.e. intra-chain exchange Jc ≈ 10.4 meV, inter-chain exchanges Jb ≈ 0.1 Jc and Ja ≈ − 0.01Jc and gap energy 2.1 meV extrapolated to T = 0 K. We also observed critical scattering at (0, 1, ½) above Tsp. The ratio of the correlation lengths ξc/ξb is in good agreement with that obtained from X-ray scattering at (½, 1, ½) by Pouget et al. This fact suggests that the Cu2+ spins fluctuate to form singlet-pair short-range order, but not to form ordinary antiferromagnetic order above Tsp.

Abstract Commensurate flux phases are investigated on a finite 4 × 4 cluster in the 2 holes doped t-J model. Qualitative agreement is found with the Gutzwiller approximated results, in particular, the magnetic energy exhibits an absolute minimum when the flux equals exactly the filling. The CFP are shown to exhibit no effective hole-hole attraction in real space.

Abstract Results of a self-consistent calculation are reported on the energy level structure of quantum wires formed by a split gate technique at GaAs/AlGaAs heterostructures in magnetic fields. The confinement potential approaches an abrupt barrier in high magnetic fields even for narrow wires for which it is nearly parabolic in the absence of a field.

Abstract We have studied the viscosity of 3He in the Al phase at various pressures with a vibrating wire viscometer in a magnetic field of 9.3 T. The data could be fitted surprisingly well using a simple model. The value of the minimum of the reduced viscosity is independent of pressure.

Abstract The flux pinning properties of impure superconducting samples are difficult to determine. This is due in part to the fact that dissipation of magnetic energy in a conductive matrix can be mistaken for flux-line flow. Additionally, ferromagnetic contamination can result in hysteresis curves similar to those caused by flux-line pinning. We present a novel solution to this problem, which employs simultaneous irradiation of a sample by two AC magnetic fields of different frequencies. The non-linear susceptibilities of ferromagnetic and superconducting phases produce intermodulation moments, whereas purely conductive phases produce only linear responses to double-frequency irradiation. The intermodulation components of the two non-linear phases are different, allowing the three phases to be distinguished from each other. We present results demonstrating this effect.