A. Briggs

Interlayer Transport in the Highly Anisotropic Misfit-Layer Superconductor (LaSe)1.14(NbSe2)

The interlayer transport in a two-dimensional superconductor can reveal a peak in the temperature as well as the magnetic field dependence of the resistivity near the superconducting transition. The experiment was performed on the highly anisotropic misfit-layer superconductor [(LaSe)(1.14)](NbSe(2)) with T(c) of 1.2 K. The effect is interpreted within the tunneling mechanism of the charge transport across the Josephson-coupled layers via two parallel channels--the quasiparticles and the Cooper pairs. Similar behavior can be found in the high-T(c) cuprates but there it is inevitably interfering with the anomalous normal state. The upper critical magnetic field can be obtained from the interlayer tunneling conductance.

Critical behaviour of the conductivity in metallic n-type InP close to the metal-insulator transition

The metal-insulator transition (MIT) induced by a magnetic field in barely metallic and compensated n-type InP has been re-examined. Using a new analysis methods, the authors have determined the magnetic field for which the conductivity changes from a metallic behaviour to a variable-range hopping regime. On the metallic side of the MIT, the electrical conductivity is found to obey sigma = sigma 0+mTs down to 60 mK; the zero-temperature conductivity can be described by a scaling law with an exponent nu =1 and there is no evidence for a minimum metallic conductivity. As the MIT is approached, they observe a clear crossover from a T1/2 to T1/3 temperature dependence of the conductivity, which is related to a competition between two length scales: the correlation length and the interaction length.

Two-dimensional behavior of the naturally layered superconductor (LaSe)1.14(NbSe2)

Abstract The three-dimensional to two-dimensional (2D) crossover of the superconducting state is presented for the naturally layered single crystal of (LaSe) 1.14 (NbSe 2 ) with the critical temperature T c of 1.23 K. Namely, the temperature dependence of the upper critical magnetic field B c2 parallel to the layers reveals an upturn at the crossover temperature T * due to the vortex confinement between the superconducting layers. Below this temperature in the 2D regime the angular dependence of B c2 displays a cusp at the field parallel to the layers. In the superconducting state the interlayer transport is accomplished in this system by the tunneling of quasiparticles and Cooper pairs.

Superconductivity induced by a magnetic field

Abstract A superconducting state, induced by a high external magnetic field, has been observed in the pseudo-ternary europium-tin-molybdenum sulfide. The present state of experimental evidence for this phenomenon is presented. The shape and the compositional dependence of the critical field-temperature phase diagram is consistent with an explanation in terms of the Jaccarino-Peter compensation effect.

Point contact spectroscopy on the ferromagnetic superconductor HoMo6S8

Abstract Point contact spectroscopy performed in single crystals of the ferromagnetic superconductor HoMo 6 S 8 , has been used to study the evolution in temperature and competition of the two order parameters. At temperatures of the order of the superconducting transition, we observe the onset of a structure in the d V /d I versus V characteristics that may be related to the development of the superconducting energy gap. At temperatures close to the ferromagnetic transitions, we also observe the growth of another structure in the d V /d I versus V characteristics that may be correlated with the development of the magnetic order parameter. This feature in the d V /d I versus V characteristic develops in a direction opposite to the structure associated with the superconducting energy gap.

Upper critical field in highly anisotropic superconductor (LaSe)1.14(NbSe2)

Abstract Magnetotransport measurements have been performed on the highly anisotropic superconducting misfit layer compound (LaSe) 1.14 (NbSe 2 ) with T c =1.23 K down to 50xa0mK and in magnetic fields up to 24 T applied at different angles with respect to the layer structure of the system. Temperature dependence of the upper critical field has been determined. Dimensionality of the system has been analyzed.

SDW transition of quenched (TMTSF)2ClO4 at high magnetic fields

Abstract The magnetic field dependence of the SDW transition (TSDW) in quenched (TMTSF)2ClO4 has been measured up to 27 T, with the field parallel to the c ∗ -direction. TSDW increases from 4.5xa0K in zero field up to 8.4xa0K at 27 T. The field dependence of TSDW has been calculated in the framework of the mean-field theory. As predicted, a quadratic behavior is observed at low field, followed by a saturation behavior. TSDW corresponding to the perfect nesting case is estimated to be 13.5xa0K. This means that the SDW phase of quenched (TMTSF)2ClO4 is strongly suppressed by the two dimensionality of the system.

Localisation and interaction effects in metallic n-type InP

Abstract We present results on the magnetic field induced metal–insulator transition (MIT) in compensated InP. The experiments were carried out at low temperatures in the range 4.2–0.066xa0K and in magnetic fields up to 11xa0T. Not too close to the MIT the electrical conductivity σ was found to obey σ = σ ( T =0)+ mT 1/2 where both the inelastic diffusion length L I ∼( σ ( T =0)) 3/2 / T 1/2 and the interaction length L T ∼( σ ( T =0)) 1/2 / T 1/2 contribute to a T 1/2 term in σ . It is convenient to develop a criterion to distinguish their contribution. It is based on the relation between the magnitude m and the zero temperature conductivity σ ( T =0).

Andreev reflection measurements on the 2D superconductor (LaSe)1.14(NbSe2)2

Abstract Point-contact spectroscopy has been performed on the quasi-two-dimensional superconducting misfit layer crystal (LaSe)1.14(NbSe2)2 with T c =5.43 K in magnetic field up to 8xa0T. The temperature dependence of the upper critical field has been determined via measurements of the superconducting order parameter in the mixed state. We found a non-zero value of the superconducting order parameter at temperatures and fields above the resistive transition indicating that a vortex melting can exist in this system.

Point contact characteristics of NbSe3-NbSe3 at low temperatures.

Abstract Point contact spectroscopy in NbSe3-NbSe3 show reproducible features. At temperatures below 4K we observe structure in the I vs V and dV/dI vs V characteristics that resemble a type of Josephson effect. d2V/dI2 vs V reveal additional structure which can be related to the Eliashberg coupled function α2(ω) F(ω).