C. Checkley | Searcharxiv

arXiv2021

Observation of Anomalous Josephson Effect in Nonequilibrium Andreev Interferometers

The first evidence of anomalous Josephson effect is reported in mesoscopic superconductor-normal metal-superconductor (SNS) junctions forming a crosslike Andreev Interferometer in the absence of magnetic and spin-orbit interactions normally required to break time-reversal and inversion symmetries. From conductance measurements of the out-of-equilibrium weak link, we determine a voltage-controlled spontaneous phase that resembles a $\varphi_0$-junction. The temperature and voltage dependences together with a dissipative term in the current-phase relation strongly suggest that the mechanism underlying the observed phenomenon relies on electron-hole asymmetries.

cond-mat.supr-con↗

arXiv2010

Andreev Interferometers in a Strong Radio Frequency Field

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 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 pi-shift with increasing RF amplitude, and consistent 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 <40ps. However there are a number of experimental features which remain unexplained; these include the drastic difference in the behaviour of the resistance at different phases as a function of RF frequency and amplitude, and the existence of a "window of transparency" where heating effects are weak enough to allow for the pi-shift. A microscopic theory describing the influence of RF radiation on Andreev interferometers is required.

cond-mat.mes-hall↗

arXiv2010

Andreev Interferometers in a strong Radio-Frequency Field

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 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 pi-shift with increasing RF amplitude, and consistent 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 <40ps. However there are a number of experimental features which remain unexplained; these include the drastic difference in the behaviour of the resistance at different phases as a function of RF frequency and amplitude, and the existence of a "window of transparency" where heating effects are weak enough to allow for the pi-shift. A microscopic theory describing the influence of RF radiation on Andreev interferometers is required.

cond-mat.mes-hall↗

arXiv2009

Anti-vortex state in cross-like nanomagnets

We report on results of computer micromodelling of anti-vortex states in asymmetrical cross-like ferromagnetic nanostructures and their practical realization. The arrays of cobalt crosses with 1 mkm branches, 100 nm widths of the branches and 40 nm thicknesses were fabricated using e-beam lithography and ion etching. Each branch of the cross was tapered at one end and bulbous at the other. The stable formation of anti-vortex magnetic states in these nanostructures during magnetization reversal was demonstrated experimentally using magnetic force microscopy.

cond-mat.mes-hall↗