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

Abstract

We have measured periodic oscillations of rectified dc voltage versus magnetic field V dc ͑B͒ 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 component͒ near the critical temperature. The Fourier spectra of these V dc ͑B͒ 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.

Quantum Magnetoresistive (hc/2e)/m-Periodic Oscillations in a Superconducting Ring

“…Moreover, the physical frequencies can be shifted by the value of k dt −1 1,2 . Fictitious low frequencies were observed in the spectra of the V (B) functions in [9,13]. It was found that for V (B) oscillations (Fig.…”

“…6) functions that are parts of the ex- It can be seen that the oscillation frequencies used to approximate the short sections 1-11 of the V 1c (B) function (Fig. 7) are as follows: f = 9f 0 (section 1); 7f 0 and 14f 0 (sections 2, 3,4,5,8,9); 10f 0 (section 6); 4f 0 , and 14f 0 (section 7); 7f 0 , and 12f 0 (sections 10, and 11).…”

Unusual quantum magnetic-resistive oscillations in a superconducting structure of two circular asymmetric loops in series

“…, and I c− (B) oscillations 1,3 in an asymmetric circular loop cannot be explained in the framework of the simple Ginzburg-Landau (GL) quasi-one-dimensional model 5 , using only the requirement of superconducting fluxoid quantization 6 . Thus, experimental studies of the unusual quantum oscillations [1][2][3]7,8 in simple superconducting circular-asymmetric structures generate many unsolved questions.…”

“…Besides the rectification of ac voltage, an asymmetric loop is interesting for other applications. Earlier 1,7,8 , it was assumed that the quantum states of a single superconducting asymmetric circular loop placed in the normal magnetic field B at T below T c can be described by the oscillating superconducting circulating current of the loop I R (B). In order to determine the time-averaged quantum states, the loop was periodically switched from superconducting state to resistive state and back by a bias alternating current (without a dc component) with an amplitude close to the critical current value.…”

“…For certain technological applications, it is necessary to know both the strength and mechanism of coupling between quantum states of loops. Earlier, an interaction (nonlinear coupling) was revealed between quantum magnetic-resistive states of two different superconducting directly connected asymmetric circular loops forming a figure-of-eight-shaped structure 7,8 . To determine the quantum state of each loop and coupling between the loops, rectified voltage V rec (B) was measured in a figureof-eight-shaped structure pierced with a magnetic flux and biased with a low-frequency current (without a dc component) and with an amplitude close to critical, at T slightly below T c 7,8 .…”