Nonmonotonous temperature dependence of Shapiro steps in YBCO grain boundary junctions

The amplitudes of the first Shapiro steps for an external signal with frequencies of 72 and 265 GHz are measured as function of the temperature from 20 to 80 K for a 6 μm Josephson grain boundary junction fabricated by YBaCuO film deposition on an yttria-stabilized zirconia bicrystal substrate. Non-monotonic dependences of step heights for different external signal frequencies were found in the limit of a weak driving signal, with the maxima occurring at different points as function of the temperature. The step heights are in agreement with the calculations based on the resistively–capacitively shunted junction model and Bessel theory. The emergence of the receiving optima is explained by the mutual influence of the varying critical current and the characteristic frequency.

Josephson Effect in MgB2/Pd/Nb Trilayer Josephson Junctions

This paper reports fabrication techniques and results of MgB2/Pd/Nb trilayer Josephson junctions. The MgB2 bottom electrode was co-evaporated by molecular beam epitaxy (MBE) technique from both magnesium and boron sources at a low substrate temperature ~ 300 °C, while the interlayer and the top niobium electrode (Pd/Nb bilayer) were deposited ex-situ using RF sputtering. The junctions exhibited and Josephson effect as well as a modulation of the critical current in a magnetic field applied in a direction normal to the junction plane. Fractional and integer Shapiro steps were observed at voltages corresponding to the frequency of the applied microwave radiation field. The products of the junctions compare well with the previously reported values. The results suggest that it should be possible to fabricate all-MgB2 and MgB2 as one of the electrodes Superconductor/Normal/Superconductor (SNS), Superconductor/Insulator/Superconductor (SIS) or even Superconductor/Ferromagnet/Superconductor (SFS) tunnel junctions with interesting characteristics and for various applications. Keywords: MgB2; all-MgB2; Josephson Tunnel junctions; trilayer devices; Niobium

Microcontroller-based simulation of a nonlinear resistive-capacitive-inductance shunted Josephson junction model and applications in electromechanical engineering

The equations, modelling a nonlinear resistive-capacitive-inductance shunted Josephson junction (NRCLJJ) subjected to various signal shapes of the electrical current, are simulated experimentally using the Arduino Uno-type microcontroller that takes benefit of its simplicity, lost cost, high precision, ease of implementation, and stability compared to the voltage-controlled oscillators (VCO) circuitry. Real time electrical signals are observed presenting various dynamics. Shapiro steps (SS) from the IV-characteristics are also obtained. These real electrical signals are then used to power an electromechanical pendulum in the second part of this work. Bifurcation diagram shows that the pendulum exhibits periodic and chaotic dynamics.

Description of Shapiro steps on the potential energy surface of a Frenkel–Kontorova model, Part II: free boundaries of the chain

We explain Shapiro steps in a Frenkel–Kontorova (FK) model for a 1D chain of particles with free boundaries. The action of an external alternating force for the oscillating structure of the chain is important here. The different ’floors’ of the potential energy surface (PES) of this model play an important role. They are regions of kinks, double kinks, and so on. We will find out that the preferable movements are the sliding of kinks or antikinks through the chain. The more kinks / antikinks are included the higher is the ’floor’ through the PES. We find the Shapiro steps moving and oscillating anywhere between the floors. They start with a single jump over the highest SP in the global valley through the PES, like in part I of this series. They finish with complicated oscillations in the PES, for excitations directly over the critical depinning force. We use an FK model with free boundary conditions. In contrast to other results in the past, for this model, we obtain Shapiro steps in an unexpected, inverse sequence. We demonstrate Shapiro steps for a case with soft ’springs’ between an 8-particle FK chain. Graphic abstract

Description of Shapiro steps on the potential energy surface of a Frenkel–Kontorova model Part I: The chain in a variable box

We explain the vibrations of a Frenkel–Kontorova (FK) model under Shapiro steps by the action of an external alternating force. We demonstrate Shapiro steps for a case with soft ‘springs’ between an 8-particles FK chain. Shapiro steps start with a single jump over the highest $$\hbox {SP}_4$$ SP 4 in the global valley through the PES. They finish with doubled, and again doubled oscillations. We study in this part I a traditional FK model with periodic boundary conditions.