Dynamics and transformations of Josephson vortex lattice in layered superconductors

We consider dynamics of Josephson vortex lattice in layered superconductors with magnetic, charge (electrostatic) and charge-imbalance (quasiparticle) interactions between interlayer Josephson junctions taken into account. The macroscopic dynamical equations for interlayer Josephson phase differences, intralayer charge and electron-hole imbalance are obtained and used for numerical simulations. Different transformations of the vortex lattice structure are observed. It is shown that the additional dissipation due to the charge imbalance relaxation leads to the stability of triangular lattice.Comment: 9 pages, 3 eps figures, to be published in Phys. Rev.

Resonances, instabilities, and structure selection of driven Josephson lattice in layered superconductors

We investigate dynamics of Josephson vortex lattice in layered high T$_{c}$ superconductors at high magnetic fields. It is shown that the average electric current depends on the lattice structure and is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode. We find the stability regions of moving lattice. It is shown that a specific lattice structure at given velocity is uniquely selected by the boundary conditions: at small velocities periodic triangular lattice is stable and looses its stability at some critical velocity. At even higher velocities a structure close to a rectangular lattice is restored.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let

A tunable macroscopic quantum system based on two fractional vortices

We propose a tunable macroscopic quantum system based on two fractional vortices. Our analysis shows that two coupled fractional vortices pinned at two artificially created \kappa\ discontinuities of the Josephson phase in a long Josephson junction can reach the quantum regime where coherent quantum oscillations arise. For this purpose we map the dynamics of this system to that of a single particle in a double-well potential. By tuning the \kappa\ discontinuities with injector currents we are able to control the parameters of the effective double-well potential as well as to prepare a desired state of the fractional vortex molecule. The values of the parameters derived from this model suggest that an experimental realisation of this tunable macroscopic quantum system is possible with today's technology.Comment: We updated our manuscript due to a change of the focus from qubit to macroscopic quantum effect

Magnetic interference patterns in 0-Pi SIFS Josephson junctions: effects of asymmetry between 0 and Pi regions

We present a detailed analysis of the dependence of the critical current I_c on the magnetic field B of 0, Pi, and 0-Pi superconductor-insulator-ferromagnet-superconductor Josephson junctions. I_c(B) of the 0 and Pi junction closely follows a Fraunhofer pattern, indicating a homogeneous critical current density j_c(x). The maximum of I_c(B) is slightly shifted along the field axis, pointing to a small remanent in-plane magnetization of the F-layer along the field axis. I_c(B) of the 0-Pi junction exhibits the characteristic central minimum. I_c however has a finite value here, due to an asymmetry of j_c in the 0 and Pi part. In addition, this I_c(B) exhibits asymmetric maxima and bumped minima. To explain these features in detail, flux penetration being different in the 0 part and the Pi part needs to be taken into account. We discuss this asymmetry in relation to the magnetic properties of the F-layer and the fabrication technique used to produce the 0-Pi junctions

Dynamic structure selection and instabilities of driven Josephson lattice in high-temperature superconductors

We investigate the dynamics of the Josephson vortex lattice in layered high-T$_{c}$ superconductors at high magnetic fields. Starting from coupled equations for superconducting phases and magnetic field we derive equations for the relative displacements [phase shifts] between the planar Josephson arrays in the layers. These equations reveal two families of steady-state solutions: lattices with constant phase shifts between neighboring layers, starting from zero for a rectangular configuration to $\pi$ for a triangular configuration, and double-periodic lattices. We find that the excess Josephson current is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode at the wave vector selected by the lattice structure. The regular lattices exhibit several kinds of instabilities. We find stability regions of the moving lattice in the plane lattice structure - Josephson frequency. A specific lattice structure at given velocity is selected uniquely by boundary conditions, which are determined by the reflection properties of electromagnetic waves generated by the moving lattice. With increase of velocity the moving configuration experiences several qualitative transformations. At small velocities the regular lattice is stable and the phase shift between neighboring layers smoothly decreases with increase of velocity, starting from $\pi$ for a static lattice. At the critical velocity the lattice becomes unstable. At even higher velocity a regular lattice is restored again with the phase shift smaller than $\pi/2$. With increase of velocity, the structure evolves towards a rectangular configuration.Comment: 28 pages, 12 figures, submitted to Phys. Rev.

Controllable plasma energy bands in a 1D crystal of fractional Josephson vortices

We consider a 1D chain of fractional vortices in a long Josephson junction with alternating $\pm\kappa$ phase discontinuities. Since each vortex has its own eigenfrequency, the inter-vortex coupling results in eigenmode splitting and in the formation of an oscillatory energy band for plasma waves. The band structure can be controlled at the design time by choosing the distance between vortices or \emph{during experiment} by varying the topological charge of vortices or the bias current. Thus one can construct an artificial vortex crystal with controllable energy bands for plasmons.Comment: 4 pages, 2 Fig

THz extended spectrum of the monodeuterated methyl formate (DCOOCH3)

Context. Laboratory spectral recordings and an accurate molecular spectral analysis of any potential interstellar molecule are essential for generating a complete spectroscopic line list. This permits predicting the frequencies and intensities of any transition so that subsequently, it can be identified in the interstellar medium. Aims. Our analysis of DCOOCH3 aims to provide a comprehensive spectral catalog that encompasses as much as possible the frequency coverage of the new-generation far-IR and submillimeter wave observation facilities. Methods. We newly measured the rotational spectrum of DCOOCH3 in the laboratory of the Jet Propulsion Laboratory in the frequency range of 0.85 to 1.5 THz. We jointly analyzed the new data with literature data using the rho axis method, which is a tool developed for the spectral analysis of molecules with large-amplitude internal CH3 rotors. Results. We fit 27 spectroscopic constants of DCOOCH3 to 3763 transitions with highest values of J = 69 and Ka = 36 of the ground torsional state with a standard (unitless) deviation of 0.97. With respect to previous work, this is a significantly better result that was obtained with 2060 more transitions, and we also achieved a better accuracy for the new parameter values.This research was supported by the FIS2011-28738-C02-02 project (MINECO, Spain), the French PCMI (Programme National de Physique Chimie du Milieu Interstellaire), and the National Natural Science Foundation of China (Grant No. 11174098). M.C. acknowledges the research stay at the Universite Paris Diderot under the Guest Faculty programme in May 2014. Portions of this paper present research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Government sponsorship is acknowledged

Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the c-axis

We studied a response of Bi-2212 mesa type structures to 100 GHz microwave radiation. We found that applying magnetic field of about 0.1 T across the layers enables to observe collective Shapiro step response corresponding to a synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At high microwave power we observed up to 10th harmonics of the fundamental Shapiro step. Besides, we found microwave induced flux-flow step position of which is proportional to the square root of microwave power and that can exceed at high enough powers 1 THz operating frequency of IJJ oscillations.Comment: 11 pages including 5 figures, accepted for publication in JETP Letter

The Phase Transition to a Square Vortex Lattice in Type-II Superconductors with Fourfold Anisotropy

We investigate the stability of the square vortex lattice which has been recently observed in experiments on the borocarbide family of superconductors. Taking into account the tetragonal symmetry of these systems, we add fourfold symmetric fourth-derivative terms to the Ginzburg-Landau(GL) free energy. At $H_{c2}$ these terms may be treated perturbatively to lowest order to locate the transition from a distorted hexagonal to a square vortex lattice. We also solve for this phase boundary numerically in the strongly type-II limit, finding large corrections to the lowest-order perturbative results. We calculate the relative fourfold $H_{c2}$ anisotropy for field in the $xy$ plane to be 4.5% at the temperature, $T_c^{\Box}$, where the transition occurs at $H_{c2}$ for field along the $z$ axis. This is to be compared to the 3.6% obtained in the perturbative calculation. Furthermore, we find that the phase boundary in the $H-T$ phase diagram has positive slope near $H_{c2}$.Comment: 15 pages including 2 figures, LaTe

Phase separation in a lattice model of a superconductor with pair hopping

We have studied the extended Hubbard model with pair hopping in the atomic limit for arbitrary electron density and chemical potential. The Hamiltonian considered consists of (i) the effective on-site interaction U and (ii) the intersite charge exchange interactions I, determining the hopping of electron pairs between nearest-neighbour sites. The model can be treated as a simple effective model of a superconductor with very short coherence length in which electrons are localized and only electron pairs have possibility of transferring. The phase diagrams and thermodynamic properties of this model have been determined within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. We have also obtained rigorous results for a linear chain (d=1) in the ground state. Moreover, at T=0 some results derived within the random phase approximation (and the spin-wave approximation) for d=2 and d=3 lattices and within the low density expansions for d=3 lattices are presented. Our investigation of the general case (as a function of the electron concentration and as a function of the chemical potential) shows that, depending on the values of interaction parameters, the system can exhibit not only the homogeneous phases: superconducting (SS) and nonordered (NO), but also the phase separated states (PS: SS-NO). The system considered exhibits interesting multicritical behaviour including tricritical points.Comment: 15 pages, 9 figures; pdf-ReVTeX, final version, corrected typos; submitted to Journal of Physics: Condensed Matte