arXiv:0712.1602 · Bulletin of the Russian Academy of Sciences Physics

Asymmetry with respect to the magnetic field direction in the interaction between the quantum states of two coupled superconducting rings

В. И. Кузнецов, А. А. Firsov, S. V. Dubonos, Marina V. Chukalina

Published Aug 1, 2007• 2 citations

Abstract

The interaction between the quantum states of two circularly asymmetric superconducting aluminum rings forming figure eight, threaded by a magnetic flux and biased by an external sinusoidal ac current with zero dc component, has been investigated. Quantum oscillations in the dependence V dc(B) of the rectified dc voltage on magnetic field for these structures have been measured at different external currents and temperatures close to critical. Fourier and wavelet analyses of the function V dc(B) have revealed, along with the two fundamental ring frequencies, various combination frequencies; this fact is indicative of interaction in the structure. Deviation of the function V dc(B) from oddness with respect to the magnetic field direction has been found for the first time.

DOI: 10.3103/s1062873807080096

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arXiv:0712.1602 · Bulletin of the Russian Academy of Sciences Physics

Asymmetry with respect to the magnetic field direction in the interaction between the quantum states of two coupled superconducting rings

В. И. Кузнецов, А. А. Firsov, S. V. Dubonos, Marina V. Chukalina

Published Aug 1, 2007• 2 citations

arXiv HTML PDF

Abstract

DOI: 10.3103/s1062873807080096

Related papers

Rectified dc voltage versus magnetic field in a superconducting asymmetric figure-of-eight-shaped microstructure

В. И. Кузнецов, А. А. Firsov, S. V. Dubonos

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We have measured periodic oscillations of rectified dc voltage versus magnetic field

{V}_{dc}(B)

in a superconducting aluminum thin-film circular-asymmetric figure-of-eight microstructure threaded by a magnetic flux and biased with a sinusoidal alternating current (without a dc component) near the critical temperature. The Fourier spectra of these

{V}_{dc}(B)

functions contain fundamental frequencies representing periodic responses of the larger and smaller asymmetric circular loops, composing the microstructure, to the magnetic field. The higher harmonics of the obtained fundamental frequencies result from the nonsinusoidal character of loop circulating currents. The presence of the difference and summation frequencies in these spectra points to the interaction between the quantum states of both loops. Magnitudes of the loop responses to the bias ac and magnetic field vary with temperature and the bias current amplitude, both in absolute values and with respect to each other. The strongest loop response appears when the average resistive state of the loop corresponds to the midpoint of the superconducting-normal phase transition.

{\mathit{T}}_{\mathit{c}}

, there is a crossover from algebraic to exponential decay of the critical current as a function of d, at a distance of the order of \ensuremath{\Elzxh}

{\mathit{v}}_{\mathit{F}}

{\mathit{k}}_{\mathit{BT}}

. Moreover, the dependence of critical current on temperature shows nonmonotonic behavior. If the Luttinger liquid is confined to a ring of circumference L, coupled capacitively to a gate voltage and threaded by a magnetic flux, the Josephson current shows remarkable parity effects under the variation of these parameters. For some values of the gate voltage and applied flux, the ring acts as a \ensuremath{\pi} junction. These features are robust against thermal fluctuations up to temperatures on the order of \ensuremath{\Elzxh}

{\mathit{v}}_{\mathit{F}}

{\mathit{k}}_{\mathit{BL}}

. For the wire geometry, we have also studied the ac-Josephson effect. The amplitude and the phase of the time-dependent Josephson current are affected by electron-electron interactions. Specifically, the amplitude shows pronounced oscillations as a function of the bias voltage due to the difference between the velocities of spin and charge excitations in the Luttinger liquid. Therefore, the ac-Josephson effect can be used as a tool for the observation of spin-charge separation. \textcopyright{} 1996 The American Physical Society.