Influence of capacitance and thermal fluctuations on the Josephson diode effect in asymmetric higher-harmonic SQUIDs,Physical Review B

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Influence of capacitance and thermal fluctuations on the Josephson diode effect in asymmetric higher-harmonic SQUIDs
Physical Review B ( IF 3.2 ) Pub Date : 2024-09-10 , DOI: 10.1103/physrevb.110.104508
G. S. Seleznev _{1,

2} , Ya. V. Fominov _{1,

2,

3}

Affiliation

Asymmetric two-junction SQUIDs with different current-phase relations in the two Josephson junctions, involving higher Josephson harmonics, demonstrate a flux-tunable Josephson diode effect (asymmetry between currents flowing in the opposite directions, which can be tuned by the magnetic flux through the interferometer loop). We theoretically investigate influence of junction capacitance and thermal fluctuations on performance of such Josephson diodes. Our main focus is on the “minimal model” with one junction in the SQUID loop possessing the sinusoidal current-phase relation and the other one featuring additional second harmonic. Capacitance generally weakens the diode effect in the resistive branch (R state) of the current-voltage characteristic (CVC) both in the absence and in the presence of external ac irradiation. At the same time, it leads to qualitatively new features of the Josephson diode effect such as asymmetry of the retrapping currents (which are a manifestation of hysteretic CVC). In particular, the limiting case of the single-sided hysteresis becomes accessible. In its turn, thermal fluctuations are known to lead to nonzero average voltages at any finite current, even below the critical value. We demonstrate that in the diode regime, the fluctuation-induced voltage can become strongly (exponentially) asymmetric. In addition, we find asymmetry of the switching currents arising both due to thermal activation and due to Josephson plasma resonances in the presence of ac irradiation.

中文翻译：

电容和热波动对不对称高次谐波 SQUID 中约瑟夫森二极管效应的影响

两个约瑟夫森结中具有不同电流相位关系的不对称双结 SQUID，涉及更高的约瑟夫森谐波，展示了通量可调谐约瑟夫森二极管效应（沿相反方向流动的电流之间的不对称性，可以通过穿过干涉仪环路）。我们从理论上研究了结电容和热波动对此类约瑟夫森二极管性能的影响。我们主要关注的是“最小模型”，其中 SQUID 环路中的一个结点具有正弦电流相位关系，另一个结点具有附加的二次谐波。无论是否存在外部交流辐射，电容通常都会削弱电流电压特性 (CVC) 电阻支路（R 状态）中的二极管效应。同时，它带来了约瑟夫森二极管效应的新特性，例如重新捕获电流的不对称性（这是迟滞 CVC 的表现）。特别是，单侧磁滞的极限情况变得容易实现。反过来，众所周知，热波动会在任何有限电流下导致非零平均电压，甚至低于临界值。我们证明，在二极管状态下，波动引起的电压可能会变得强烈（指数）不对称。此外，我们发现由于热激活和交流辐射存在下的约瑟夫森等离子体共振而产生开关电流的不对称性。

更新日期：2024-09-10

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