对高温超导体的本征约瑟夫森结在外加电磁辐射下的电荷不平衡效应进行了详细的数值模拟。我们表明，电荷不平衡是负责的Shapiro步骤的值增加的非平衡参数的斜率。结之间的耦合导致斜率值沿堆栈的分布。非周期性边界条件将IV-特征中的Shapiro阶跃从由$V_{ss}=\hbar f /(2e)$确定的正则位置移动，其中$f$是外部辐射的频率。这一事实使模糊的解释实验发现夏皮罗步移的电荷不平衡效应。
英文摘要：
Detailed numerical simulations of intrinsic Josephson junctions of high temperature superconductors under external electromagnetic radiation are performed taking into account a charge imbalance effect. We demonstrate that the charge imbalance is responsible for a slope in the Shapiro step the value of which increases with a nonequilibrium parameter. Coupling between junctions leads to the distribution of the slope's values along the stack. The nonperiodic boundary conditions shift the Shapiro step in IV-characteristics from the canonical position determined by $V_{ss}=\hbar f /(2e)$, where $f$ is a frequency of external radiation. This fact makes ambiguous the interpretation of the experimentally found Shapiro step shift by the charge imbalance effect.
It is widely believed that superconducting junctions involving topological insulators and hosting Majorana-like bound states may exhibit unusual "fractional" ($4π$-periodic) ac Josephson effect. Accordingly, "fractional" Shapiro steps on the current-voltage characteristics of such junctions are expected to occur under external microwave radiation. Here, we microscopically evaluate Shapiro steps in topologically trivial highly transparent superconducting weak links. The key features recovered within our analysis -- including, e.g., the so-called "missing" Shapiro steps -- turn out to be similar…
We report the experimental observation of half-integer Shapiro steps in the strong ferromagnetic Josephson junction (Nb-NiFe-Nb) by investigating the current-phase relation under radiofrequency microwave excitation. The half-integer Shapiro steps are robust in a wide temperature range from T = 4 to 7 K. The half-integer Shapiro steps could be attributed to co-existence of 0- and pi-states in the strong ferromagnetic NiFe Josephson junctions with the spatial variation of the2 NiFe thickness. This scenario is also supported by the high-resolution transmission electron microscopy characterization…
The Majorana zero-energy modes (MZMs) residing at the boundary of topological superconductors have attracted a great deal of interest recently, as they provide a platform to explore fundamental physics such as non-Abelian statistics, as well as fault-tolerant quantum computation. Period doubling of Shapiro steps in a Josephson junction under microwave irradiation has been regarded as strong evidence for the emergence of the MZMs at the junction edges. However, questions remain as to how the Shapiro steps respond to the presence of a 4π-periodic Josephson current. In this study, we investigated…
A superconducting quantum interference device (SQUID) comprising 0- and $π$-Josephson junctions (JJs), called $π$-SQUID, is studied by the resistively shunted junction model. The $π$-SQUID shows half-integer Shapiro-steps (SS) under microwave irradiation at the voltage $V$ = $(\hbar/2e)Ω(n/2)$, with angular frequency $Ω$ and half-integer $n$/2 in addition to integer $n$. We show that the $π$-SQUID can be a $π$-qubit with spontaneous loop currents by which the half-integer SS are induced. Making the 0- and $π$-JJs equivalent is a key for the half-integer SS and realizing the $π$-qubit.
We show that ultrasound can induce the Shapiro steps (SS) in the charge-density-wave (CDW) state. When ultrasound with frequency $ω$ and a dc voltage are applied, the SS occur at the current $I$ $\propto$ $nω$ with integer $n$. Even and odd multiples of SS are represented by two couplings between the CDW and ultrasound. Although an ac voltage bias with frequency $ω$ induces the SS at $I\propto nω$, the ultrasound bias enhances the odd multiples more strongly than the even ones. This is the difference between the ultrasound and the ac voltage. Since the SS cause abrupt peaks in the $dV/dI$, the…
University of Florence（佛罗伦萨大学）；European Laboratory for Nonlinear Spectroscopy (LENS)（欧洲非线性光谱学实验室）；Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO)（意大利国家光学研究所）；Quantum Research Centre, Technology Innovation Institute（技术创新研究所量子研究中心）
All fractional Shapiro steps in the RSJ model with two Josephson harmonics
L. D. Landau Institute for Theoretical Physics RAS（朗道理论物理研究所）；Moscow Institute of Physics and Technology（莫斯科物理技术学院）；Laboratory for Condensed Matter Physics, HSE University（高等经济大学凝聚态物理实验室）
We report on the influence a preferential magnetic vortices motion has on the magnitude of the inverse ac Josephson effect (the appearance of dc current Shapiro steps) and the coherent operation of asymmetrical parallel arrays of YBaCuO Josephson junctions (JJ) irradiated with microwave (MW) radiation in the presence of an applied magnetic field B. The preferential direction of motion of the Josephson vortices is due to the asymmetry-induced ratchet effect and has a dramatic impact: for a particular positive dc bias current I when the flux-flow is robust multiple pronounced Shapiro-steps are o…
Joule overheating poisons the fractional ac Josephson effect in topological Josephson junctions
在三维拓扑绝缘体（TI）表面上设计的拓扑约瑟夫森结在常规Andreev束缚态的连续体中具有马约拉纳束缚态（MBS）。这些MBS的不同特征在于$4π$ -它们的能量-相位关系的周期性，其产生分数交流约瑟夫森效应和在$r\!f$照射下的奇夏皮罗台阶的抑制。然而，最近的实验表明，有几个，或者只是第一个，奇怪的夏皮罗步骤是失踪，对解释投下怀疑。在这里，我们表明，约瑟夫森结上定制的大带隙三维TI Bi $_2$ Se $_3$表现出分数交流约瑟夫森效应作用于第一夏皮罗步骤。用一个改进的反向分流结模型，我们证明了高阶奇Shapiro台阶的弹性可以用焦耳过热驱动的热中毒来解释。此外，我们发现在夏皮罗叶之间的节点，这提供了一个直接的和新颖的签名的MBS所携带的电流的残余超电流。我们的研究结果展示了拓扑约瑟夫森结中的热效应的关键作用，并支持马约拉纳起源的奇数夏皮罗步骤的部分抑制。
Phase-Locking of Vortex Lattices Interacting with Periodic Pinning
我们研究Shapiro步骤的涡旋晶格相互作用的周期性钉扎阵列驱动的交流和直流电流。涡流是由间隙涡运动通过周期性势而产生的，周期性势是由被钉扎在钉扎部位的涡产生的。在B_B < B < 2.25B_B的情况下，观察到Shapiro台阶，其中最显著的台阶出现在间隙涡晶格具有高度对称性的情况下。锁相电流阶跃的宽度作为交流驱动的幅度的函数被发现遵循与理论一致的贝塞尔函数。
In the presence of a 4$π$-periodic contribution to the current phase relation, for example in topological Josephson junctions, odd Shapiro steps are expected to be missing. While missing odd Shapiro steps have been observed in several material systems and interpreted in the context of topological superconductivity, they have also been observed in topologically trivial junctions. Here, we study the evolution of such trivial missing odd Shapiro steps in Al-InAs junctions in the presence of an in-plane magnetic field $B^θ$. We find that the odd steps reappear at a crossover $B^θ$ value, exhibitin…
