arXiv subjects

Yu. M. Shukrinov

Publications and source records attributed to Yu. M. Shukrinov.

65 records · Page 4Linked to original sources

arXiv2008

Created-by-current states in long Josephson junctions

Critical curves "critical current - external magnetic field" of long Josephson junctions with inhomogeneity and variable width are studied. We demonstrate the existence of the regions of magnetic field where some fluxon states are stable only, if the external current through the junction is different from zero. Position and size of such regions depend on length of the junction, its geometry, parameters of inhomogeneity and form of the junction. The noncentral (left and right) pure fluxon states are appeared in the inhomogeneous Josephson junction with increase in the junction length. We demonstrate new bifurcation points with change in width of the inhomogeneity and amplitude of the Josephson current through the inhomogeneity.

cond-mat.supr-con↗

arXiv2008

Experimental manifestation of the breakpoint region in the current-voltage characteristics of intrinsic Josephson junctions

The experimental evidence of the breakpoint on the current-voltage characteristics (IVCs) of the stacks of intrinsic Josephson junctions (IJJs) is presented. The influence of the capacitive coupling on the IVCs of Bi$_2$Sr$_2$CaCu$_2$O$_y$ IJJs has been investigated. At 4.2 K, clear breakpoint region is observed on the branches in the IVCs. It is found that the hysteresis observed on the IVC is suppressed due to the coupling compared with that expected from the McCumber parameter. Measurements agree well with the results obtained by the theoretical model.

cond-mat.supr-con↗

arXiv2007

Influence of coupling between junctions on breakpoint current in intrinsic Josephson junctions

We study theoretically the current-voltage characteristics of intrinsic Josephson junctions in high-$T_c$ superconductors. An oscillation of the breakpoint current on the outermost branch as a function of coupling $α$ and dissipation $β$ parameters is found. We explain this oscillation as a result of the creation of longitudinal plasma waves at the breakpoint with different wave numbers. We demonstrate the commensurability effect and predict a group behavior of the current-voltage characteristics for the stacks with a different number of junctions. A method to determine the wave number of longitudinal plasma waves from $α$- and $β$-dependence of the breakpoint current is suggested. We model the $α$- and $β$-dependence of the breakpoint current and obtain good agreement with the results of simulation.

cond-mat.supr-con↗

arXiv2007

Peculiarities of the stacks with finite number of intrinsic Josephson junctions

We study the breakpoint region on the outermost branch of current-voltage characteristics of the stacks with different number of intrinsic Josephson junctions. We show that at periodic boundary conditions the breakpoint region is absent for stacks with even number of junctions. For stacks with odd number of junctions and for stacks with nonperiodic boundary conditions the breakpoint current is increased with number of junctions and saturated at the value corresponding to the periodic boundary conditions. The region of saturation and the saturated value depend on the coupling between junctions. We explain the results by the parametric resonance at the breakpoint and excitation of the longitudinal plasma wave by the Josephson oscillations. A way for the diagnostics of the junctions in the stack is proposed.

cond-mat.supr-con↗

arXiv2006

Common features of vortex structure in long exponentially shaped Josephson junctions and Josephson junctions with inhomogeneities

We study vortex structure in three different models of long Josephson junctions: exponentially shaped Josephson junction and Josephson junctions with resistor and shunt inhomogeneities in barrier layer. Numerical calculations of the possible magnetic flux distributions and corresponding bifurcation curves have done. For these three models the critical curves ``critical current-magnetic field'' are constructed. We develop an idea of the equivalence of exponentially shaped Josephson junction and rectangular junction with distributed inhomogeneity and demonstrate that at some parameters of shunt and resistor inhomogeneities at the ends of the junction the corresponding critical curves are very close to the exponentially shaped one.

cond-mat.supr-con↗

arXiv2006

Vortex structure in long Josephson junction with two inhomogeneities

A report of numerical experiment results on long Josephson junction with one and two rectangular inhomogeneities in the barrier layer is presented. In case of one inhomogeneity we demonstrate the existence of the asymmetric fluxon states. The disappearance of mixed fluxon-antifluxon states when the position of inhomogeneity shifted to the end of the junction is shown. In case with two inhomogeneities the change of the amplitude of Josephson current through the inhomogeneity at the end of junction makes strong effect on the stability of the fluxon states and smoothes the maximums on the dependence ``critical current - magnetic field''.

cond-mat.supr-con↗

arXiv2006

Coordinate transformation in the model of long Josephson junctions: geometrically equivalent Josephson junctions

The transition from the model of a long Josephson junction of variable width to the model of a junction with a coordinate-dependent Josephson current amplitude is effected through a coordinate transformation. This establishes the correspondence between the classes of Josephson junctions of variable width and quasi-one-dimensional junctions with a variable thickness of the barrier layer. It is shown that for a junction of exponentially varying width the barrier layer of the equivalent quasi-one-dimensional junction has a distributed resistive inhomogeneity that acts as an attractor for magnetic flux vortices. The curve of the critical current versus magnetic field for a Josephson junction with a resistive microinhomogeneity is constructed with the aid of a numerical simulation, and a comparison is made with the critical curve of a junction of exponentially varying width. The possibility of replacing a distributed inhomogeneity in a Josephson junction by a local inhomogeneity at the end of the junction is thereby demonstrated; this can have certain advantages from a technological point of view.

cond-mat.supr-con↗

arXiv2005

Effect of coupling on scheme of hysteresis jumps in current-voltage characteristics of intrinsic Josephson junctions in high- superconductors

We report the numerical calculations of the current-voltage characteristics of intrinsic Josephson junctions in high- superconductors. The charging effect at superconducting layers is taken into account. A set of equations is used to study the non-linear dynamics of the system. In framework of capacitively coupled Josephson junctions model we obtain the total number of branches using fixed initial conditions for phases and their derivatives. The influence of the coupling constant αon the current-voltage characteristics at fixed parameter β(β^2=1/β_c, where β_c is McCumber parameter) and the influence of αon β-dependence of the current-voltage characteristics are investigated. We obtain the α-dependence of the branch's slopes and branch's endpoints. The obtained results show new features of the coupling effect on the scheme of hysteresis jumps in current-voltage characteristics of intrinsic Josephson junctions.

cond-mat.supr-con↗

arXiv2004

Static vortices in long Josephson junctions of exponentially varying width

A numerical simulation is carried out for static vortices in a long Josephson junction with an exponentially varying width. At specified values of the parameters the corresponding boundary-value problem admits more than one solution. Each solution (distribution of the magnetic flux in the junction) is associated to a Sturm--Liouville problem, the smallest eigenvalue of which can be used, in a first approximation, to assess the stability of the vortex against relatively small spatiotemporal perturbations. The change in width of the junction leads to a renormalization of the magnetic flux in comparison with the case of a linear one-dimensional model. The influence of the model parameters on the stability of the states of the magnetic flux is investigated in detail, particularly that of the shape parameter. The critical curve of the junction is constructed from pieces of the critical curves for the different magnetic flux distributions having the highest critical currents for the given magnetic field.

cond-mat.supr-con↗

arXiv2004

Vortex structure in exponentially shaped Josephson junctions

We report the numerical calculations of the static vortex structure and critical curves in exponentially shaped long Josephson junctions for in-line and overlap geometries. Each solution of the corresponding boundary value problem is associated with the Sturm-Liouville problem whose minimal eigenvalue allows to make a conclusion about the stability of the vortex. The change in width of the junction leads to the renormalization of the magnetic flux in comparison to the case of a linear one-dimensional model. We study the influence of the model's parameters and, particularly, the shape parameter on the stability of the states of the magnetic flux. We compare the vortex structure and critical curves for the in-line and overlap geometries. Our numerically constructed critical curve of the Josephson junction matches well with the experimental one.

cond-mat.supr-con↗

arXiv2000

Modeling of Tunneling Spectroscopy in HTSC

The tunneling density of states of HTSC is calculated taking into account tight binding band structure, group velocity, and tunneling directionality for s-wave and d-wave gap symmetry. The characteristic density of states has quasiparticle peaks' asymmetry, flat s-wave and cusplike d-wave case subgap behavior, and asymmetric background. We consider that the underlying asymmetry of the conductance peaks is primarily due to the features of quasiparticle energy spectrum, and the d-wave symmetry enhances the degree of the peaks' asymmetry. Increasing of the lifetime broadening factor changes the degree of tunneling conductance peaks' asymmetry, and leads to the confluence of the quasiparticle and van Hove singularity peaks.

cond-mat.supr-con↗