G. Nieva

Photoinduced enhancement of superconductivity

We show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa2Cu3Ox thin films by photoexcitation. Upon laser illumination the critical temperature increases while the resistivity of the material decreases. The relaxation back to the original state is very slow, of the order of days at room temperature. The existence of this effect opens the possibility of fabricating weak‐link devices with in situ tunable superconducting characteristics.

Hybridization, hole localization and pair breaking in the high Tc superconducting system Y1-xPrxBa2Cu3O7-δ

Abstract The Y 1- x Pr x Ba 2 Cu 3 O 7- δ ( δ ≈ 0.05) system has a rich temperature—praseodymium concentration ( T - x ) phase diagram consisting of a metal—insulator transition at x cr ≈0.6, high T c superconductivity in the metallic phase (0⩽ x ≤ x cr ), and antiferromagnetic ordering of the Cu 2+ and praseodymium ions at Neel temperatures T N (Cu) > T N (Cu)> T N (Pr) in the insulating phase ( x cr ≤ x ⩽1). In the metallic phase, T c decreases monotonically with x and vanishes near x cr , the dependence of T c on pressure P and the upper critical field on temperature are both anomalous, and the low temperature specific heat can be resolved into a large γΓ contribution, reminiscent of heavy fermion behavior, and a spin 1 2 Kondo anomaly; in the insulating phase, the values of T N (Pr) are anomalously large. These phenomena are briefly reviewed within the framework of a picture that is based on appreciable hybridization of the praseodymium localized 4f states and the CuO 2 valence band states. A phenomenological model that incorporates the annihilation of mobile holes in the CuO 2 planes and superconducting electron pair breaking by the praseodymium ions can describe T c ( x , P ) for x ≤ 0.2.

On narrowing of the resistive superconducting transition in applied magnetic fields and positive curvature in Hc2(T) in the (Gd1−xPrx)Ba2Cu3O7−δ system

Abstract The superconducting transition temperature T c and the temperature dependence of the upper critical field H c2 were measured resistively on polycrystalline samples in the (Gd 1− x Pr x )Ba 2 Cu 3 O 7−δ system. The experimental results reveal that T c decreases monotonically with increasing x and vanishes at x ≈0.49. Whereas H c2 of a sample with x =0.10 has an almost linear temperature dependence and the superconducting transition broadens with increasing magnetic field, a sample with x =0.45 shows strong positive curvature in the H c2 versus temperature curve and narrowing of the superconducting transition width with increasing magnetic field. Both phenomena observed in the sample with x =0.45 can be explained qualitatively in terms of a negative exchange interaction between the superconducting charge carriers and the Pr 4f electrons.

First-order phase transition of the vortex lattice in twinned YBa 2 Cu 3 O 7 single crystals in tilted magnetic fields

We present an exhaustive analysis of transport measurements performed in twinned

Changes in the Pr-induced TC depression of 123 compounds by chemical pressure

{\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}

Photoexcitation effects in YBa2Cu3Ox

single crystals which establishes that the vortex solid-liquid transition is first order when the magnetic field H is applied at an angle

Enhancement of Superconductivity by Photoexcitation

\ensuremath{\theta}

Photoinduced changes in the transport properties of oxygen-deficient YBa2Cu3Ox.

away from the direction of the twin planes. We show that the resistive transitions are hysteretic and the

Superconductivity and magnetism in Eu1-xPrxBa2Cu3O7- delta.

V\ensuremath{-}I

Low-temperature specific heat of the Y1-xPrxBa2Cu3O7- delta system.

curves are nonlinear, displaying a characteristic S shape at the melting line