The states of two phase-coupled superconducting rings have been investigated. Multiple current states have been revealed in the dependence of the critical current on the magnetic field. The performed calculations of the critical currents and energy states in a magnetic field have made it possible to interpret the experiment as the measurement of energy states into which the system comes with different probabilities because of the equilibrium and non-equilibrium noises upon the transition from the resistive state to the superconducting state during the measurement of the critical current
Fluxoid dynamics in superconducting thin film rings
我们已经测量了动态的个别磁通量进入和离开undertoped高温超导体Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$，使用可变的样品温度扫描SQUID显微镜的图案化薄膜环。这些结果可以定性地描述使用一个模型，其中的磁通量数的变化由热激活的珍珠涡的成核，和运输的珍珠涡跨越，环壁。
At a superconductor interface with a ferromagnetic insulator (FI), the FI acts to induce a local exchange field within the S layer, which in the presence of spin-orbit interaction promotes a phase modulated superconducting state. Here we demonstrate that within a thin superconducting loop that is partially proximitized by a FI, spontaneous currents form with a magnetization-orientation-dependent chirality with sizable shifts in Little-Parks oscillations. Furthermore, the critical temperature of the loop is also magnetization-orientation-dependent and conversely, the superconducting transition …
Thermal fluctuations of the Josephson current $I$ induced by the magnetic flux through a ring of $N$ superconducting grains are studied. When a half-fluxon is threading the ring, $I$ exhibits incoherent transitions between the two degenerate states due to thermal phase slips. We propose a new numerical method to deal with both equilibrium and dynamic properties of Josephson systems. Computed transition rate has the form $Γ= A(N)\exp[-B(N)/T]$, where $B(N)$ agrees with the analytical result derived for the energy barrier associated with phase slips. In the non-degenerate case (e.g., at a quarte…
We study the ratchet effect in a narrow pinning-free superconductive ring based on time-dependent Ginzburg-Landau (TDGL) equations. Voltage responses to external dc an ac currents at various magnetic fields are studied. Due to asymmetric barriers for flux penetration and flux exit in the ring-shaped superconductor, the critical current above which the flux-flow state is reached, as well as the critical current for the transition to the normal state, are different for the two directions of applied current. These effects cooperatively cause ratchet signal reversal at high magnetic fields, which …
Superconductivity is shown to be completely destroyed in thin mesoscopic or nanoscopic rings closed by the junction with a noticeable interfacial pair breaking and/or a Josephson coupling, if a ring's radius r is less than the minimum radius r_min. The quantity r_min depends on the phase difference across the junction, or on the magnetic flux that controls the phase difference in the flux-biased ring. It also depends on the Josephson and interfacial effective coupling constants, and in particular, on whether the ring is closed by 0 or pi junction. The current-phase relation is substantially mo…
The quantum dynamics of quasi-one-dimensional ring with varying electron filling factor is investigated in presence of external electric field. The system is modeled within Hubbard Hamiltonian with attractive Coulomb correlation, which results in superconducting ground state when away from half-filling. The electric field is induced by applying time-dependent Aharonov-Bohm flux in the perpendicular direction. To explore the non-equilibrium phenomena arising from the field, we adopt exact diagonalization and Crank-Nicolson numerical method. With increase in electric field strength, the electron…
We studied resistance oscillations in two types of superconducting mesoscopic Nb rings. In a simple superconducting ring device, a resistance oscillation with a period of the quantized magnetic flux h/2e was clearly observed. On the other hand, in a micro-bridge ring device where two-narrow parts are embedded in parallel and work as superconductor-normal metal-superconductor junctions, higher harmonic resistance oscillations were obtained when the measurement current was well-tuned. We argue that such higher harmonic resistance oscillations can be detected even in the micro-bridge Nb supercond…
We describe measurements of the thermally-activated transitions between fluxoid states of a single isolated superconducting ring. We compare these measurements with theoretical predictions in which all of the relevant parameters are determined via independent characterization of the same ring. This no-free-parameters comparison shows qualitative agreement over a wide range of temperatures. We discuss possible origins for the remaining discrepancies between the data and theory, in particular the choice of model for the superconducting order parameter's damping.
Magnetic quantum periodicity in the dc voltage is observed when asymmetric rings are switched between superconducting and normal state by a noise or ac current. This quantum effect is used for detection of a non-equilibrium noise with the help of a system of 667 asymmetric aluminum rings of $1 \ μm$ in diameter connected in series. Any noise down to the equilibrium one can be detected with the help of such system with enough great number of asymmetric rings.
We theoretically investigate the critical bias current $j_c$ for a superconducting (SC) ring in a magnetic field. Based on the Ginzburg-Landau theory, we show that $j_c$ exhibits a Little-Parks (LP) oscillation as a function of the magnetic flux passing through the ring, similarly to the LP oscillation in the SC transition temperature. It is also found that for a spin-triplet SC ring, the ${\bf d}$-vector rotates to yield a larger $j_c$, forming a texture along the circumference of the ring. Experimental implications of our result are discussed.
We revisit the critical penetration of Pearl vortices in narrow superconducting flat rings cooled in magnetic fields. Scanning superconducting quantum interference device microscopy measurements showed how magnetic field penetrates and vortices are trapped in flat rings made of amorphous MoGe thin films. Counting the number of trapped vortices for each image, we found that the vortices are completely excluded from the ring annulus when the applied field $H$ is below a threshold field $H_{\rm{p}}$: Above this field, the vortices increase linearly with field. The obtained values of $H_{\rm{p}}$ …
Multiple phase slips phenomena in mesoscopic superconducting rings
通过模拟具有周期边界条件的含时Ginzburg-Landau方程，研究了介观一维圆环在外磁场中的行为。我们分析了从一个亚稳态开始的相位滑移现象的稳定性和不同的可能演化。我们发现一个稳定性条件有关的绕组数的初始解决方案和数量的磁通量子穿透环。多个相位滑移解决方案的分析是基于分析结果和仿真。两个特征时间u的比例的作用进行了研究的情况下，多个相位滑移过渡。我们发现，如果u>>1，连续多个相位滑移将比同时多个相位滑移更有利。如果u<<1 the opposite is true and we confirm that u>>1往往是达到基态的必要条件。讨论了朗之万噪声对相变动力学的影响。
The observations the dc voltage on asymmetric superconducting ring testify that one of the ring segments is a dc power source. The persistent current flows against the total electric field in this segment. This paradoxical phenomenon is observed when the ring or its segments are switched between superconducting and normal state by non-equilibrium noises. We demonstrate that the dc voltage and the power increase with the number of the identical rings connected in series. Large voltage and power sufficient for practical application can be obtained in a system with a sufficiently large number of …
