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We demonstrate that a multiply connected superconducting structure in combination with a perpendicularly magnetized magnetic dot can be used as a current source for superconducting elements and as an external phase shifter. The concept has been tested by measuring the superconducting Tc(B) phase boundary and critical current of an Al superconducting loop placed on the top of a micron-sized Co/Pd magnetic dot. A pronounced asymmetry in the voltage–current characteristic of the loop with respect to the polarity of the external magnetic field, as well as a shift of the Tc(B) phase boundary along the field axis indicate the presence of a persistent current in the loop. [ABSTRACT FROM AUTHOR]

An approach to the Ginzburg–Landau problem for superconducting regular polygons is developed making use of an analytical gauge transformation for the vector potential A which gives An=0 for the normal component along the boundary line of different symmetric polygons. As a result the corresponding linearized Ginzburg–Landau equation reduces to an eigenvalue problem in the basis set of functions obeying Neumann boundary condition. Such basis sets are found analytically for several symmetric structures. The proposed approach allows for accurate calculations of the order parameter distributions at low calculational cost (small basis sets) for moderate applied magnetic fields. This is illustrated by considering the nucleation of superconductivity in squares, equilateral triangles and rectangles, where vortex patterns containing antivortices are obtained on the Tc–H phase boundary. The calculated phase boundaries are compared with the experimental Tc(H) curves measured for squares, triangles, disks, rectangles, and loops. The stability of the symmetry consistent solutions against small deviations from the phase boundary line deep into the superconducting state is investigated by considering the full Ginzburg–Landau functional. It is shown that below the nucleation temperature symmetry-switching or symmetry-breaking phase transitions can take place. The symmetry-breaking phase transition has the same structure as the pseudo-Jahn-Teller instability of high symmetry nuclear configurations in molecules. The existence of these transitions is predicted to be strongly dependent on the size of the samples. [ABSTRACT FROM AUTHOR]

A superconducting microtriangle is proposed to be used as a field-dependent diode. A dc voltage generated by the triangle induced by an applied ac drive is observed close to the superconducting/normal phase boundary. This effect is due to the superposition of the asymmetric screening currents in the triangle and the ac drive. The sign of the dc voltage is an alternating function of the applied magnetic field that reflects switching of the direction of the screening currents in the structure. [ABSTRACT FROM AUTHOR]

We have studied a system consisting of a superconducting Al strip placed close to a perpendicularly magnetized Co/Pd rectangle. The stray fields of the rectangle produce a nonhomogeneous magnetic field in the superconductor. These stray fields can efficiently compensate the self-field inside the current-carrying superconductor. We have observed a current-polarity dependence of the critical current. The compensation effects are strongly dependent on the current in the superconductor and also on the temperature. The studied configuration is easily tunable for a large range of applied currents. [ABSTRACT FROM AUTHOR]

We have studied the nucleation of superconductivity in a mesoscopic Al disk with a Co/Pd magnetic dot placed on the top by measuring the normal/superconducting phase boundary T[sub c](B). The measurements have revealed a pronounced asymmetry in the phase boundary with respect to the direction of the applied magnetic field, indicating an enhancement of the critical field when an applied magnetic field is oriented parallel to the magnetization of the magnetic dot. The theoretical T[sub c](B) curve is in a good agreement with the experimental data. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]