Thermal effect in phase-periodic electron transport in disordered mesoscopic normal metal/superconductor structures

We report measurements of the temperature dependence of the amplitude of phase-periodic conductance oscillations in disordered normal metal (Ag) structures, attached to a superconducting (Al) wire at two points. The amplitude of oscillations reaches its maximum at temperatureT ^*, when the Thouless energy is of the order ofk _B T. The results are in agreement with recent calculations by Nazarov and Stoof [Phys. Rev. Lett. 76 (1996) 823].     

Superconducting phase coherent electron transport in proximity conical ferromagnets

We report superconducting phase-periodic conductance oscillations in ferromagnetic wires with interfaces to conventional superconductors. The ferromagnetic wires were made of Ho, a conical ferromagnet. The distance between the interfaces was much larger than the singlet superconducting penetration depth. We explain the observed oscillations as due to the long-range penetration of an unusual helical triplet component of the order parameter that is generated at the superconductor/ferromagnet interfaces and maintained by the intrinsic rotating magnetization of Ho.     

Andreev probe of persistent current states in superconducting quantum circuits

Using the extraordinary sensitivity of Andreev interferometers to the superconducting phase difference associated with currents, we measure the persistent current quantum states in superconducting loops interrupted by Josephson junctions. Straightforward electrical resistance measurements of the interferometers give a continuous readout of the states, allowing us to construct the energy spectrum of the quantum circuit. The probe is estimated to be more precise and faster than previous methods, and can measure the local phase difference in a wide range of superconducting circuits.     

Triplet superconductivity in a ferromagnetic vortex

We argue that triplet superconductivity can be conveniently realized in hybrid superconductor-ferromagnet (S-F) structures with a ferromagnetic vortex. We demonstrate that due to proximity-induced long-range triplet pairing such S-F-S junctions can sustain appreciable supercurrent which can be directly measured in experiments. Depending on the contact geometry either zero- or π-junction regime can be realized in the system under consideration.     

Phase-sensitive reentrance into the normal state of mesoscopic SNS structures

Normal (N) metallic (Ag) mesoscopic conductors with two superconducting (S) faces (Al), arranged mirror-symmetrically relative to the streamlines of the current, periodically switch into the normal state as the superconducting phase difference Δϕ between the NS boundaries approaches the values Δϕ =(2n+1)π, n=0,1,2,..., irrespective of temperature and applied voltage. For Δϕ =2nπ and low applied voltages the conductance passes through a maximum and approaches the normal value as temperature decreases (reentrance). As the voltage subsequently increases, the conductance increases and passes through a maximum. As the phase difference moves away from the values Δϕ=2nπ, the maxima shift in the direction of low temperatures and voltages. The latter result shows unequivocally that in our metal structures it is necessary to take into account the next-order corrections to the “weak” proximity effect approximation. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 489–494 (10 April 1998)     

Thermal effect in the phase-periodic conductance of disordered mesoscopic N/S structures

We report measurements of the temperature dependence of the amplitude of phase-periodic conductance oscillations in disordered (diffusive) normal metal (Ag) structures attached to a superconducting (Pb) wire at two points. The oscillation amplitude exceeds the value of e ²/h by orders of magnitude and reaches its maximum at a temperature corresponding to the Thouless energy. The results support the recent theory of Nazarov and Stoof, [Phys. Rev. Lett. 76, 823 (1996)], which takes into account the characteristic energy dependence of the change in the diffusion coefficient of quasiparticles in a normal conductor due to Andreev reflections. The line shape of the oscillations as a function of the superconducting phase difference is found to be extremely sensitive to the quality of N/S interfaces and shows hysteretic behavior in interferometers with specially prepared clean interfaces. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 11, 789–793 (10 December 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Phase states of multiterminal mesoscopic normal-metal-superconductor structures

We study a mesoscopic normal-metal structure with four superconducting contacts, two of which are joined into a loop. The structure undergoes transitions between three (meta)stable states, with different phase configurations triggered by nonequilibrium conditions. These transitions result in spectacular changes in the magnetoresistance. We find a qualitative agreement between the experiments and a theory based on the quasiclassical Keldysh formalism.