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We report highly sensitive specific heat measurements on mesoscopic superconducting loops at low temperature. These mesoscopic systems exhibit thermal properties significantly different from that of the bulk materials. The measurement is performed on a silicon membrane sensor where 450 000 superconducting aluminium loops are deposited through electron beam lithography, under an applied magnetic field. Each entry of a vortex is associated to a jump in the specific heat of few thousands of Boltzmann constant kB indicating the existence of phase transitions. The periodicity of this sequential phase transitions is a nontrivial behaviour and varies strongly as the temperature is decreased. The successive phase transitions are well described by the Ginzburg-Landau theory of superconductivity. The presence of metastable states is responsible for the n[uppercase_phi_synonym]0 (n=1, 2, 3...) periodicity of the discontinuities of the measured specific heat. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

I review free and trapped Bose-Einstein condensates (BECs) [1, 2, 3, 4, 5]. In an isotropic harmonic potential V(r) = 1/2Mω2r2, the single-particle ground state introduces a new intrinsic scale of length [the ground-state size d = h/(Mω)] and energy [the ground-state energy E0 = 3/2hω]. When the trap rotates [6, 7, 8], there is a critical angular velocity for the appearance of one or a few quantized vortices. For more rapid rotation [9, 10, 11, 12, 13] the condensate contains a vortex array. The resulting centrifugal forces expand the condensate radially and shrink it axially; thus the condensate becomes effectively two-dimensional. If the external rotation speed approaches the frequency of the radial harmonic confining potential, the condensate enters the “lowest-Landau-level” regime, and a simple description again becomes possible [14, 15]. Eventually, the system is predicted to make a quantum phase transition to a highly correlated state analogous to the fractional quantum Hall states of electrons in a strong magnetic field [16, 17, 18, 19, 20]. [ABSTRACT FROM AUTHOR]

Layered organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br shows a step-like softening in the sound velocity below the superconducting transition temperature. In this study, we have measured the sound velocity in the superconducting state of κ-(BEDT-TTF)2Cu[N(CN)2]Br in the applied magnetic field for various directions. The sound velocity as a function of the applied magnetic field shows remarkable elastic anomalies around H = 2 T. It was found that, the magnetic field parallel to the conducting planes of κ-(BEDT-TTF)2Cu[N(CN)2]Br, the sound velocity shows a sharp peak, which is considered to be related to the pinning by Josephson vortices. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Vortex lattice compression moduli in ceramic YBaCuO are studied by measurement of ac response U in the hollow of a cylinder existing in the mixed state. Investigations were performed at stationary magnetic fields H up to 1200 Oe, when the elastic moduli have a non-local character resulting in saturation of the U(H) dependence at large values of H. The analysis of the frequency dependence of the studied response permits to conclude that the wave-vector of vortex lattice deformation decreases with increase of excitation frequency. The penetration of the signal into the hollow increases at reduction of the frequency down to values about 5 kHz; at the further frequency reduction abrupt strengthening of the signal screening is observed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Two-dimensional vortex dynamics in a ratchet planar pinning potential (PPP) in the presence of thermal fluctuations is considered on the basis of a Fokker-Planck equation. Explicit expressions for two new nonlinear anisotropic voltages (longitudinal and transverse with respect to the current direction) are derived and analyzed. The physical origin of these odd (with respect to magnetic field or transport current direction reversal) voltages is caused by the interplay between the even effect of vortex guiding and the ratchet asymmetry. Both new voltages are going to zero in the linear regimes of the vortex motion (i.e. in the thermoactivated flux flow (TAFF) and ohmic flux flow (FF) regimes) and have a bump-like current or temperature dependence in the vicinity of the highly nonlinear resistive transition from TAFF to FF. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]