ABSTRACT
We experimentally study the influence of 1-40 GHz radiation on the resistance of normal (N) mesoscopic conductors coupled to superconducting (S) loops (Andreev interferometers). At low radio-frequency (RF) amplitudes we observe the usual h/2e superconducting phase periodic resistance oscillations as a function of applied magnetic flux. We find that the oscillations acquire a π-shift with increasing RF amplitude, and consistently with this result the resistance at fixed phase is an oscillating function of the RF amplitude. The results are explained qualitatively as a consequence of two processes. The first is the modulation of the phase difference between the N/S interfaces by the RF field, with the resistance adiabatically following the phase. The second process is the change in the electron temperature caused by the RF field. From the data, the response time of the Andreev interferometer is estimated to be τ(f) < 40 ps. However there are a number of experimental features which remain unexplained; these include the drastic difference in behaviour of the resistance at Ï = π and 0 as a function of the RF frequency and amplitude, and the existence of a 'window of transparency' where heating effects are weak enough to allow for the π-shift. A microscopic theory describing the influence of RF radiation on Andreev interferometers is required.
Subject(s)
Algorithms , Computer Simulation , Radio Waves , Interferometry , Radiation , Time FactorsABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
