We present switching current measurements in niobium-aluminum oxide-niobium underdamped Josephson rings. Underdamped Josephson rings display hysteretic current-voltage curves which can be characterized by their switching current, the value of applied current at which the junctions switch to the energy-gap voltage. The value of the switching current is strongly affected by temperature and by the presence of fluxons in the system. We observe a very small voltage (0.2 nV) across the ring prior to switching, indicating a low-velocity fluxon diffusion state before the jump to a full running state. In analogy with previous work on single junctions, we analyze the switching current data with the process of thermal activation over a dissipation barrier, where the system switches from a low velocity state to a high velocity state. We find that our data agrees qualitatively with this description, further supporting the observation of fluxon diffusion.
Switching Current Measurements of EuBa2Cu3Oy Intrinsic Josephson Junctions
研究了两种不同各向异性参数γ（=（m*c/m*ab）1/2）的EuBa 2 Cu 3 O y（Eu 123）本征约瑟夫森结（IJJs）的开关动力学.与Bi 2212中的弱耦合IJJ相比，由于Eu 123 IJJ的强耦合性质，在它们的开关电流分布P（I）中观察到了与单堆约瑟夫森结的热激活逃逸模型的显著偏离。这表明在高温液态He中观察到宏观量子隧穿。
Multi-Junction Switching in Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ Intrinsic Josephson Junctions
研究了多结开关（MJS）的动力学：阵列中的多个本征约瑟夫森结（IJJ）同时切换到有限电压状态。通过改变串联连接到Bi $_2$ Sr $_{1.6}$ La $_{0.4}$ CuO $_{6+δ}$ IJJ阵列的负载电阻，成功地调谐了多开关结（$N$）的数量。宏观量子隧穿机制中$N$的逃逸率的独立性表明MJS是一个$successive$开关过程而不是$collective$过程。MJS的起源解释的负载曲线的梯度和准粒子分支的开关电流在电流-电压平面的相对幅度。
Experiments on the distributions of switching currents in Josephson junctions are sensitive probes of the mechanism by which a junction changes abruptly to a finite voltage state. At low temperatures data exhibit smooth and gradual deviations from the expectations of the classical theory of thermal activation over the barrier in the tilted washboard potential. In this paper it is shown that if a very small proportion of the noise energy entering the apparatus at room temperature survives filtering and reaches the sample, it can enhance the escape rate sufficiently to replicate experimental obs…
Josephson junctions and superconducting wires when probed with current pulses exhibit stochastic switching from superconducting to a stable non-zero voltage state. Electrical current dependence of the switching probability (so called S-curve) or switching current distribution is a fingerprint of the physics governing the escape process. This work addresses the criterion of independent switching event in a series of switching experiments. Treating Josephson junction as an electrical coin with current-tuned switching probability we investigate effect of correlation between switching events on th…
Analysis of Josephson junctions switching time distributions for the detection of single microwave photons
Università di Salerno（萨莱诺大学）；INFN, Gruppo Collegato Salerno（意大利国家核物理研究所萨莱诺协作组）；INFN, Laboratori Nazionali di Frascati（意大利国家核物理研究所弗拉斯卡蒂国家实验室）；University of Roma Tre（罗马第三大学）；Univ. of Sannio（桑尼奥大学）
We test the effect of an external RF field on the switching processes of magnetic Josephson junctions (MJJs) suitable for the realization of fast, scalable cryogenic memories compatible with Single Flux Quantum logic. We show that the combined application of microwaves and magnetic field pulses can improve the performances of the device, increasing the separation between the critical current levels corresponding to logical '0' and '1'. The enhancement of the current level separation can be as high as 80% using an optimal set of parameters. We demonstrate that external RF fields can be used as …
Thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions and hysteresis
Comparative study of macroscopic quantum tunneling in Bi_2Sr_2CaCu_2O_y intrinsic Josephson junctions with different device structures
研究了两种器件结构的$_2$ $_2$ O $_y$本征约瑟夫森结（IJJ）的宏观量子隧穿（MQT）.一种是只有两个或三个IJJ的纳米厚小台面结构，另一种是在窄桥结构上堆叠数百个IJJ。实验结果表明，对于单约瑟夫森结，从零电压状态开始的第一次开关事件的开关电流分布与传统理论吻合较好，表明前一种器件结构从热激活到MQT区的交叉温度与后一种器件结构一样高。结合MQT机制中量子化能级之间的多光子跃迁的观察，这些结果强烈地表明，所观察到的MQT行为是高$T_c$铜酸盐中单个IJJ所固有的，与器件结构无关。从第一电阻状态的第二切换事件的切换电流分布，这是仔细区分从第一切换，也比较了两个器件结构之间。尽管在热传递环境的差异，两个设备的第二切换事件被发现显示出类似的温度无关的行为高达比第一切换的交叉温度高得多的温度。我们认为，它不能解释的自加热由于耗散电流后的第一次切换。作为可能的候选者，MQT过程的第二开关和电子温度的有效增加，由于准粒子注入进行了讨论。
We present a study of the first and second switches (SWs) with nearly identical switching current $I_{\rm SW}$ in Bi$_2$Sr$_2$Ca$_{0.85}$Y$_{0.15}$Cu$_2$O$_y$ intrinsic Josephson junctions (IJJs). In contrast to early studies where a large difference between $I_{\rm SW}^{\rm 1st}$ and $I_{\rm SW}^{\rm 2nd}$ was observed, a crossover temperature $T_{\rm cr}$ to the quantum phase escapes for the 2nd SW is strongly reduced $(\sim$2.8~K) and agrees with that for the 1st SW. This confirms that the anomalous enhancement of $T_{\rm cr}^{\rm 2nd}$, commonly observed in the IJJs with $I_{\rm SW}^{\rm 1…
In this work we give a characterization of the RF effect of memory switching on Nb-Al/AlOx-(Nb)-Pd$_{0.99}$Fe$_{0.01}$-Nb Josephson junctions as a function of magnetic field pulse amplitude and duration, alongside with an electrodynamical characterization of such junctions, in comparison with standard Nb-Al/AlOx-Nb tunnel junctions. The use of microwaves to tune the switching parameters of magnetic Josephson junctions is a step in the development of novel addressing schemes aimed at improving the performances of superconducting memories.
We study analytically and numerically the influence of the quasiparticle charge imbalance on the dynamics of the asymmetric Josephson stack formed by two inequivalent junctions: the fast capacitive junction $JJ_{1}$ and slow non-capacitive junction $JJ_{2}$. We find, that the switching of the fast junction into resistive state leads to significant increase of the effective critical current of the slow junction. At the same time, the initial switching of the slow junction may either increase or decrease the effective critical current of the fast junction, depending on ratio of their resistances…
We predict that the amplitude of the Josephson current through an antiferromagnetic weak link changes by several orders of magnitude upon rotation of the Néel order parameter characterizing the staggered magnetic order. This occurs due the presence of spin-orbit coupling arising from structural inversion asymmetry which makes the band gap in the antiferromagnet highly sensitive to the staggered order parameter direction. We also demonstrate that when phase-biasing the junction, magnetization dynamics is induced which switches the direction of the Néel vector in the antiferromagnet. These resul…
Unequivocal signatures of Majorana zero energy modes in condensed matter systems and manipulation of the associated electron parity states are highly sought after for fundamental reasons as well as for the prospect of topological quantum computing. In this Letter, we demonstrate that a ring of Josephson coupled topological superconducting islands threaded by magnetic flux and attached to a quantum dot acts as an excellent parity-controlled probe of Majorana mode physics. As a function of flux threading through the ring, standard Josephson coupling yields a $Φ_0=h/(2 e)$ periodic features corre…
We discuss the effects of thermal noise on the magnetic response of a lateral ferromagnetic Josephson junction with spin-orbit coupling and out-of-plane magnetization. The direction of the magnetic moment in the ferromagnetic layer can be inverted by using controlled current pulses. This phenomenon is due to the magnetoelectric effect that couples the flowing charge current and the magnetization of the ferromagnet. We investigate the magnetization reversal effect versus intrinsic parameters of the ferromagnet, such as the Gilbert damping and strength of the spin-orbit coupling. We estimate the…
