The high-frequency response of a Josephson junction is numerically investigated. The resistively shunted junction (RSJ) model and the resistively and capacitively shunted junction (RCSJ) model are employed. Simulation results for the Shapiro steps are different between the two models. The difference with respect to the RF current is explained by employing a simple resistor and capacitor model.
The high-frequency response of a Josephson junction is numerically investigated. The resistively shunted junction (RSJ) model and the resistively and capacitively shunted junction (RCSJ) model are employed. Simulation results for the Shapiro steps are different between the two models. The difference with respect to the RF current is explained by employing a simple resistor and capacitor model.
Experimental I-V curves of microwave-driven Josephson tunnel junctions with resistive shunts are reported. The results are in very good agreement with numerical calculations using the resistively shunted junction model. In the low-frequency regime there are three distinct regions in the I-V curves and two different types of Shapiro steps. It is demonstrated that the overall shape of the I-V curves can be explained by using an adiabatic interpretation of the junction response. The two different types of Shapiro steps are related to a compensation effect between dc and rf bias currents.
Abstract The pursuit of high-speed response and precise reconstruction of phase reversal within Josephson junction constitutes the principal research objectives for the device model in the superconducting single flux quantum (SFQ) circuits. The proposing of the resistive-capacitive-inductive-shunted junction (RCLSJ) model by incorporating a shunted inductance on the classical resistive-capacitive-shunted junction (RCSJ) model, indeed achieves a more accurate description of the Current–Voltage ( I – V ) characteristics of Josephson junctions. However, the effectiveness of the RCLSJ model in dynamic simulations of SFQ circuits has not yet been verified. We proposed a simple and convenient test structure for D flip-flop (DFF) circuits to obtain the variation of its bias margin over a wide frequency sweep range. Post-simulations using the RCLSJ model were performed for DFF circuits. It was found that there are still matching problems between the simulations and tests, especially in the higher frequency region. Based on the junction area structure and layout application under the SIMIT-Nb03 process, a corrected RCLSJ model, designated as the RCLSJv model, was developed. This model mainly reassigns the parasitic inductance of the junction area and introduces correction coefficients by fitting the test data. The validity of the model has been verified through the comprehensive fitting of multiple sets of DFFs’ test data. In comparation with the RCSJ model, the deviation between the test and simulation results was successfully confined within 3%. Notably, in the frequency range above 60 GHz, the matching degree exhibits a remarkable enhancement, with an improvement factor ranging from 2 to 5 times.
High Tc Josephson junctions have IcRn products as large as a few mV at liquid helium temperature, and hence, the frequency normalized by IcRn∕Φ0 becomes on the order of 10−3 for a gigahertz (GHz) microwave signal. (Here, Ic, Rn, and Φ0 are the critical current, the normal resistance, and a flux quantum, respectively.) It is well known that a microwave-current-driven Josephson junction does not exhibit clear Shapiro steps under such low frequency conditions. Instead of Shapiro steps, however, we often observe a current-step-like structure in the current–voltage curve of YBa2Cu3O7−δ grain boundary Josephson junctions coupled to a GHz signal. In this article, we present a model analysis for such current-step-like structures. Two types of device models are employed: a simple resistively and capacitively shunted junction model and a rf-field-driven two-junction superconducting quantum interference device model. Numerical results of the latter model agree with the experimental results, which indicates that the envelope of small Shapiro steps, including the effects of microwave-induced motion of flux quanta, appears as a current-step-like structure in a high Tc Josephson device coupled to a GHz microwave.
Abstract Josephson junctions based on superconducting materials are fundamental components for quantum detection, quantum communication and quantum computers. An accurate behavioral model of Josephson junctions is the prerequisite for predicting various superconducting circuits. In this study, We present a resistively and capacitively shunted junction (RCSJ) model-based behavioral-level model for the current-voltage characteristics of Josephson junctions. This model accurately predicts the current-voltage characteristics and their temperature dependencies of Josephson junctions made of different materials under three typical working modes: underdamped voltage-driven, overdamped current-driven, and underdamped current-driven. Additionally, it forecasts the critical current and superconducting energy gap characteristics with respect to temperature, as well as the constraint relationship between the shunt resistance, superconducting energy gap, and critical current. Comparing the measured data with the simulation predictions, the model has an average accuracy of 85.9%, which illustrates the reliability of the model.
Results on analytical and computational investigations of high frequency dynamics of Josephson junctions, characterized by nonzero capacitance and the second harmonic in the current-phase relation are presented. These attributes each influence on behaviour of integer Shapiro steps and lead to formation of non-integer Shapiro steps. Analytic theory of the integer and non-integer Shapiro steps has been developed for so-called high frequency limit. The analytical and numerical results are compared with experimental data for hybrid heterostructures YBCO/Au/Nb. Detector response for the case of high fluctuation level has been considered as well.
The nonlinear response of a short Josephson Junction (JJ), being irradiated simultaneously with two high-frequency signals, has been studied in the framework of the nonlinear Resistively-Shunted Junction (RSJ) Model. One of the signals, hereafter referred to as "probe signal", has a small amplitude I/sub pr/<I/sub c/ (I/sub c/ is the critical current of the JJ) and frequency f/sub pr/, and is used to monitor the response of the junction to the other high-power signal with amplitude I/sub pm/ and frequency f/sub pm/, hereafter referred to as "pump signal". Varying the frequency ratio f(pm)/f/sub pr/ from 0.5 to 100, and the current amplitude of the probe signal from 0.01 to 0.9 of I/sub c/, we found that the dependence of the junction impedance at the frequency f/sub pr/, Z/sub s//sup fpr/, versus I/sub pm/ preserves its general features, independent of f/sub pm//f/sub pr/ and I/sub pr//I/sub c/ values. At the same time, some particular features, like negative values of Re(Z/sub s//sup fpr/) and "fine" structure of the steps in Z/sub s//sup fpr/ (I/sub pm/ are observed for f/sub pm//f/sub pr/<1 and for particular values of I/sub pr//I/sub c/. In general, the behavior of Z/sub s//sup pr/(I/sub pm/) is rather different from that predicted by the nonlinear RSJ model for a short JJ in the regime of single-frequency irradiation, when one and the same signal plays the roles of the pump and the probe signals simultaneously. Possible applications of the model are briefly discussed.