arXiv:1812.00732 · Low Temperature Physics

The effect of alternating current on the current states of a quantum interferometer shunted by a superconducting inductance

S. I. Link, V. P. Koverya, A. V. Krevsun, С. И. Бондаренко

Published Nov 1, 2018• 0 citations

Abstract

The patterns of reversible changes in the critical current and discrete current states of a structure in the form of a superconducting quantum interferometer shunted by superconducting inductance, as a result of passing an alternating transport current through the structure and applying an external alternating magnetic field simultaneously with a direct transport current, was established. A new type of discrete stationary state was discovered during the transition of the interferometer to the resistive state caused by the combined action of direct and alternating transport currents.

DOI: 10.1063/1.5060965

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arXiv:1812.00732 · Low Temperature Physics

The effect of alternating current on the current states of a quantum interferometer shunted by a superconducting inductance

S. I. Link, V. P. Koverya, A. V. Krevsun, С. И. Бондаренко

Published Nov 1, 2018• 0 citations

arXiv HTML PDF

Abstract

DOI: 10.1063/1.5060965

Related papers

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We have investigated asymmetrically shunted Nb/Al-AlO

_x

/Nb direct current (dc) superconducting quantum interference devices (SQUIDs). While keeping the total resistance

R

identical to a comparable symmetric SQUID with

R^{-1} = R_1^{-1} + R_2^{-1}

, we shunted only one of the two Josephson junctions with

R = R_{1,2}/2

. Simulations predict that the optimum energy resolution

ε

and thus also the noise performance of such an asymmetric SQUID can be 3--4 times better than that of its symmetric counterpart. Experiments at a temperature of 4.2\,K yielded

ε\approx 32\,\hbar

for an asymmetric SQUID with an inductance of

22\,\rm{pH}

. For a comparable symmetric device

ε= 110\,\hbar

was achieved, confirming our simulation results.

L

incorporating a point contact as a weak link which determines the critical supercurrent in the ring,

{i}_{c}

. A phenomenological model for the stationary quantum states of the system as a function of an applied field is developed. The dynamic behavior is obtained directly from the time dependence of the applied fields. Experiments demonstrating both the stationary and the time-dependent magnetic behavior are described. The stationary behavior was obtained with a magnetometer incorporating a weakly connected ring as a sensor to measure the flux through the ring under test. The experimental results confirm the phenomenological model if the critical curr\`ent

{i}_{c}

is greater than $\frac{{\ensuremath{\Phi}}_{0}}{2L(1+\ensuremath{\gamma})}$, where ${\ensuremath{\Phi}}_{0}=\frac{h}{2e}$ is the flux quantum and $\ensuremath{\gamma}$ is a material and geometric parameter which is usually small compared to unity. In the regime $L{i}_{c}>\frac{{\ensuremath{\Phi}}_{0}}{2(1+\ensuremath{\gamma})}$, the quantum states are discrete, and the transitions between states are well defined and irreversible. If the critical current is not too large, the transitions generally occur only between adjacent states; that is, $\ensuremath{\Delta}k=\ifmmode\pm\else\textpm\fi{}1$. At large critical current, multiple quantum jumps are observed. On the other hand, if $L{i}_{c}<\frac{{\ensuremath{\Phi}}_{0}}{2(1+\ensuremath{\gamma})}$, the quantum states merge into one another continuously and reversibly. In this case the magnetic behavior inthe neighborhood of the half-quantum points is related to the depairing or gapless regime in superconductivity. Measurements of the ac properties of the weakly connected ring at 30 MHz are interpreted directly in terms of the static properties under the influence of a time-varying applied field. In fact, no qualitative corrections to the theory are expected up to frequencies of the order of the superconducting energy gap.