We report measurements of switching-current distribution (SWCD) from a phase-diffusion branch to a quasiparticle-tunneling branch as a function of temperature in a cuprate-based intrinsic Josephson junction. Contrary to the thermal-activation model, the width of the SWCD increases with decreasing temperature, down to 1.5 K. Based on the multiple-retrapping model, we quantitatively demonstrate that the quality factor of the junction in the phase-diffusion regime determines the observed temperature dependence of the SWCD.
Thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions and hysteresis
Comment on "Composite excitation of Josephson phase and spin waves in ferromagnetic Josephson junctions" (S.Hikino, M.Mori, S.Takahashi, and S.Maekawa, arXiv:1009.3551)
Josephson radiation is a useful signature for detecting Majorana zero modes in topological superconductors. We study the Josephson radiation of the underdamped topological Josephson junction within the quantum resistively and capacitively shunted junction model. We show that the quantum dynamics of the Majorana two-level system induce oscillatory patterns in the Josephson emission spectra. With the Floquet method, we obtain analytical results for these oscillatory patterns and find that they are well described by Bessel functions. We perform numerical simulations to verify the analytical resul…
We highlight the reproducibility and level of control over the electrical properties of YBa$_2$Cu$_3$O$_7$ Josephson junctions fabricated with irradiation from a focused helium ion beam. Specifically, we show the results of electrical transport properties for several junctions fabricated using a large range of irradiation doses. At the lower end of this range, junctions exhibit superconductor-normal metal-superconductor (SNS) Josephson junction properties. However, as dose increases there is a transition to electrical characteristics consistent with superconductor-insulator-superconductor (SIS…
Collective resonance modes of Josephson vortices in sandwiched stack of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ intrinsic Josephson junctions
在长结极限下，观察到Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+x}$单晶的本征约瑟夫森结（IJJ）的电流-电压特性中，低偏置涡旋流分支在密集约瑟夫森涡旋态分裂成多个子分支.每个子分支对应于串联耦合的约瑟夫森结中的等离子体模式。分裂成低偏置线性子分支的斜率和子分支间模式切换字符的扩展是在良好的定量协议与预测的弱，但有限的结间电容耦合模型与电感耦合。这表明电容耦合在精确描述串联堆叠IJJ中的涡旋动力学中的作用的重要性。
We study magnetization reversal in a $φ_0$ Josephson junction with direct coupling between magnetic moment and Josephson current. Our simulations of magnetic moment dynamics show that by applying an electric current pulse, we can realize the full magnetization reversal. We propose different protocols of full magnetization reversal based on the variation of the Josephson junction and pulse parameters, particularly, electric current pulse amplitude, damping of magnetization and spin-orbit interaction. We discuss experiments which can probe the magnetization reversal in $φ_0$-junctions.
The most important practical characteristic of a Josephson junction is its critical current. The shape of the junction determines the specific form of the magnetic-field dependence of the its Josephson current. Here we address the magnetic diffraction patterns of specially shaped planar Josephson tunnel junctions. We focus on a wide ensemble of generalized ellipses, called superellipses, which retain the second order symmetry. We analyze the implications of this type of isometry and derive the explicit expressions for the threshold curves of superelliptic Josephson junctions. A detailed study …
The development of superconducting memory and logic based on magnetic Josephson junctions relies on an understanding of junction properties and, in particular, the dependence of critical current on external magnetic flux (i.e. Fraunhofer patterns). With the rapid development of Josephson junctions with various forms of inhomogeneous barrier magnetism, Fraunhofer patterns are increasingly complex. In this paper we model Fraunhofer patterns for magnetic Josephson junctions in which the barrier magnetic susceptibility is position- and external magnetic field dependent. The model predicts anomalou…
The physics of Josephson tunnel junctions drastically depends on their geometrical configurations. The shape of the junction determines the specific form of the magnetic-field dependence of the its Josephson current. Here we address the magnetic diffraction patterns of specially shaped planar Josephson tunnel junctions in the presence of an in-plane magnetic field of arbitrary orientations. We focus on a wide ensemble of junctions whose shape is invariant under point reflection. We analyze the implications of this type of isometry and derive the threshold curves of junctions whose shape is the…
We investigate stationary charge imbalance effect in the system of coupled overdamped Josephson junctions. We show that coupling between junction and nonzero stationary charge imbalance in the resistive state bring to a decrease of the Josephson frequency in the Josephson junctions of the stack. The formed difference in Josephson frequency leads to the nonuniform switch to the Shapiro step regime in the presence of external electromagnetic radiation and appearance of kinks of voltage on the IV-characteristics of the stack. We also show that stationary charge imbalance brings to the slope of th…
Vortex-flow electromagnetic emission in stacked intrinsic Josephson junctions
通过观察Josephson涡旋流电流-电压特性中的多个子分支，证实了在Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+x}$的叠层本征约瑟夫森结中存在由约瑟夫森涡旋晶格运动激发的集体横向等离子体模.我们还观察到了约瑟夫森涡旋晶格与集体横等离子体模共振产生微波辐射的现象，这为研制约瑟夫森涡旋流电磁振荡器提供了可能。
Superconductivity is a result of quantum coherence at macroscopic scales. Two superconductors separated by a metallic or insulating weak link exhibit the AC Josephson effect - the conversion of a DC voltage bias into an AC supercurrent. This current may be used to activate mechanical oscillations in a suspended weak link. As the DC voltage bias condition is remarkably difficult to achieve in experiments, here we analyse theoretically how the Josephson effect can be exploited to activate and detect mechanical oscillations in the experimentally relevant condition with purely DC current bias. We …
We report on the noise properties of ion-irradiated YBa$_2$Cu$_3$O$_7$ Josephson junctions. This work aims at investigating the linewidth of the Josephson oscillation with a detector response experiment at $\simeq$132 GHz. Experimental results are compared with a simple analytical model based on the Likharev-Semenov equation and the de Gennes dirty limit approximation. We show that the main source of low-frequency fluctuations in these junctions is the broadband Johnson noise and that the excess ($\frac{1}{f}$) noise contribution does not prevail in the temperature range of interest, as report…
We present a unified description of a junction between $s$-wave (BCS) superconductors and a junction between $p$-wave superconductors in a topologically nontrivial phase, which relies on a scattering state expansion. We compute Josephson current and thermal noise in the two kinds of junction and exhibit some characteristic features for a junction of two topological superconductors hosting Majorana zero-energy modes.
We report the electrical transport in vertical Josephson tunnel junctions (area 400 $μm$$^2$) using GdBa$_2$Cu$_3$O$_7$$_{-δ}$ electrodes and SrTiO$_3$ as an insulating barrier (with thicknesses between 1 nm and 4 nm). The results show Josephson coupling for junctions with SrTiO$_3$ barriers of 1 nm and 2 nm. The latter displays a Josephson of 8.9 mV at 12 K. This value is larger than the usually observed in planar arrays of junctions. Our results are promising for the development of superconducting electronic devices in the terahertz regime.
The phase dynamics of the stack of long Josephson junctions has been studied. Both inductive and capacitive couplings between Josephson junctions have been taken into account in the calculations. The IV--curve, bias current dependence of radiation power and dynamics of each JJs of the stack have been investigated. The coexistence of the charge traveling wave and fluxon states has been observed. This state can be considered as a new collective excitation in the system of coupled Josephson junctions. We demonstrate that the observed collective excitation leads to the decreasing of radiation powe…
