Abstract: We report the results of ac sheet conductance measurements performed on fully frustrated square arrays of Josephson junctions whose coupling energy is periodically modulated in one of the principal lattice directions. Such systems are predicted to exhibit two distinct transitions: a low-temperature Ising-like transition triggered by the proliferation of domain walls and a high-temperature transition driven by the vortex unbinding mechanism of the Beresinskii-Kosterlitz-Thouless (BKT) theory. Both the superfluid and dissipative components of the conductance are found to exhibit features which unambiguously demonstrate the existence of a double transition whose properties are consistent with the Ising-BKT scenario.

Abstract: Hexagonal CePd2-xNixAl3 exhibits a crossover from a Kondo lattice showing magnetic order at T(N)similar or equal to2.8 K for xless than or equal to0.2 to intermediate valence (IV) for x-->2. Though T-N(x) is weakly affected upon Pd/Ni substitution before vanishing at finite temperature, the Kondo temperature T-K progressively increases. Above xsimilar or equal to0.3 the phase boundary no longer exists and strong spin fluctuations cause pronounced deviations from a Fermi-liquid ground state before the IV regime is established for xgreater than or equal to1. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We present electrical resistivity and specific heat measurements of alloys on the Rh rich side of the phase diagram of the Ce(Rh1-xPdx)(2)Si-2 system. We compare these results with those obtained at intermediate and low Rh concentrations. The analysis of the concentration and temperature dependence of the entropy and of the scaling behaviour of C-et(T) and rho(T) clearly confirm a separation of the magnetic phase diagram into two regions: the region x less than or equal to 0.3, showing a concentration independent characteristic temperature for the 4f-electrons with T-0 approximate to 45 K, while for x > 0.3, T-0 decreases to T-0(x = 1) approximate to 15 K. At low Pd-content, T-N decreases very rapidly from T-N = 36 K in pure CeRh2Si2 to T-N = 18 K at x = 0.1. With higher Pd concentration T-N stabilizes at T-N approximate to 15 K whereas the magnitude of the anomalies in C-et(T) and in the susceptibility around T-N are further reduced and disappear at x approximate to 0.3. This differs from the behavior found on the Pd-rich side, where T-N decreases continuously to zero with increasing Rh content. The pronounced differences observed between both phase boundaries and the drastic effect of doping on the Rh rich side suggest an itinerant character in CeRh2 Si-2, in contrast with the localized character of CePd2Si2. Further evidence for the itinerant character of CeRh2Si2 is given by the rho(T) dependence observed for x less than or equal to 0.3, which scales with rho(T) of the prototype itinerant compound YCo2.

Abstract: We present the evolution of magnetic and structural properties of Y1-xPrxBa2Cu3Oy (xsimilar to0.5 and x = 1) single crystals and polycrystalline materials when the oxygen concentration y is varied from under- to overdoping. We have found a monotonous evolution of the Pr Neel temperature for x = 1 samples and a maximum of the superconducting critical temperature for the xsimilar to0.5 samples. The structural properties as detected by X-ray diffraction and Raman spectroscopy show no instabilities when crossing the optimal doping region as was found in the x = 0 material. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: Multiterminal measurements using experimental technique on twinned and untwinned YBa2Cu3O7-? crystals were presented. Inhomogeneous current distribution acting upon an uncorrelated vortex system showed that the dissipation of voltage at the top was larger than at the bottom. The behavior of the current voltage curves showed that the result Vtop = Vbot was a consequence of the limited voltage sensitivity.