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Nonequilibrium steady state conditions induced by a dc current can alter the physical properties of strongly correlated electron systems. In this regard, it was recently shown that dc current can trigger novel electronic states, such as current-induced diamagnetism, which cannot be realized in equilibrium conditions. However, reversible control of diamagnetism has not been achieved yet. Here, we demonstrate reversible in situ control between a Mott insulating state and a diamagnetic semimetal-like state by a dc current in the Ti-substituted bilayer ruthenate ${\mathrm{Ca}}_{3}({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{)}_{2}{\mathrm{O}}_{7}$ ($x=0.5%$). By performing simultaneous magnetic and resistive measurements, we map out the temperature vs current-density phase diagram in the nonequilibrium steady state of this material. The present results open up the possibility of creating novel electronic states in a variety of strongly correlated electron systems under dc current.

Autoresonance is a self-sustained resonance mechanism due to a driving force whose frequency monotonically varies with time. We theoretically show that the autoresonance mechanism allows an efficient switching of perpendicular magnetization by spin-orbit spin-transfer torques. We find that a threshold current for the autoresonant switching can be much smaller than that of conventional spin-orbit torque switching driven by a DC current. Moreover, the suggested scheme allows fully deterministic switching without the help of any external field.

We demonstrate experimentally the operation of a deterministic Josephson ratchet with tunable asymmetry. The ratchet is based on a φ Josephson junction with a ferromagnetic barrier operating in the underdamped regime. The system is probed also under the action of an additional dc current, which acts as a counterforce trying to stop the ratchet. Under these conditions the ratchet works against the counterforce, thus producing a nonzero output power. Finally, we estimate the efficiency of the φ Josephson junction ratchet.

Using the Kadanoff-Baym-Keldysh formalism, we employ nonequilibrium dynamical mean-field theory to exactly solve for the nonlinear response of an electron-mediated charge-density-wave-ordered material. We examine both the dc current and the order parameter of the conduction electrons as the ordered system is driven by the electric field. Although the formalism we develop applies to all models, for concreteness, we examine the charge-density-wave phase of the Falicov-Kimball model, which displays a number of anomalous behaviors including the appearance of subgap density of states as the temperature increases. These subgap states should have a significant impact on transport properties, particularly the nonlinear response of the system to a large dc electric field., 10 pages, 8 figures

The general solution for ballistic electronic transport through double-barrier Josephson junctions is derived. We show the existence of a regime of phase-coherent transport in which the supercurrent is proportional to the single barrier transparency and the way in which this coherence is destroyed for increasing interlayer thickness. The quasiparticle dc current at arbitrary voltage is determined., 4 pages, 2 figures, submitted to Phys. Rev. B

We study the energy barrier for flux entry of a geometric origin in type-I superconducting strips using magneto-optical observations of the flux structure. The magnetic field is applied perpendicularly to the broad surface and, optionally, a dc current is sent along the strip. As a direct manifestation of this barrier, the appearance of flux-free zones at the edges of the strip is observed. The width of these zones, the field for first-flux penetration, and the critical current originated due to the geometrical barrier are measured. The dependence of these parameters on the geometry of the sample, applied field, transport current, and temperature presented here is in good qualitative agreement with a recent theory by Benkraouda and Clem.

We calculate the dc current-voltage ($I\ensuremath{-}V$) relation for a ballistic superconductor-normal metal-superconductor (${S}_{1}N{S}_{2}$) junction, where the two superconducting contacts have different energy gaps (${\ensuremath{\Delta}}_{2}g~{\ensuremath{\Delta}}_{1}g~0$). Several new features appear in the $I\ensuremath{-}V$ relation as it evolves from a $\mathrm{NS}$ junction (${\ensuremath{\Delta}}_{1}=0$) to the symmetric $\mathrm{SNS}$ junction (${\ensuremath{\Delta}}_{1}={\ensuremath{\Delta}}_{2}$). The dc current ${I}_{0}$ flowing at small voltages is ${I}_{0}=4\frac{e{\ensuremath{\Delta}}_{1}}{h}$, and is different from the critical current ${I}_{c}$. The differential conductance changes abruptly at $eV={\ensuremath{\Delta}}_{2}\ensuremath{-}{\ensuremath{\Delta}}_{1}$ due to the loss of a single Andreev reflection from the larger-gap superconductor. Finally, the voltages ${\ensuremath{\Delta}}_{n}$ at which subharmonic gap structures appear in the $I\ensuremath{-}V$ relation for temperatures ${k}_{B}T\ensuremath{\simeq}{\ensuremath{\Delta}}_{2}$ depend on both energy gaps ${\ensuremath{\Delta}}_{1}$ and ${\ensuremath{\Delta}}_{2}$. We find a systematic way to classify this subgap structure.

We report numerical studies of phase locking in two-dimensional (2D) arrays of Josephson junctions. In the conventional 2D arrays biased with dc current in the horizontal (X) direction, the phase-locked solution is only possible in arrays with no disorder. In the presence of disorder in the junction critical currents, we see vertical (Y) columns of phase locked clusters form in the array with no intercolumn locking. As an extension, we introduced a geometry called XY-biased array, where the array is biased in both X and Y directions. In XY-biased array we found a dynamical state, where all junction voltages are strictly dc and the only oscillating components are the supercurrents in each junction. This dynamical state is stable against experimentally achievable disorder in the junction critical currents. \textcopyright{} 1996 The American Physical Society.

The response of $360\ifmmode^\circ\else\textdegree\fi{}$ domain walls in narrow magnetic stripes to applied dc and ac currents, investigated by micromagnetic simulation, differs qualitatively from the response of $180\ifmmode^\circ\else\textdegree\fi{}$ domain walls. The $360\ifmmode^\circ\else\textdegree\fi{}$ domain-wall velocity scales with a dc current but is independent of an applied magnetic field along the stripe. An annihilation process occurs at a critical dc current density that varies with the applied field. When a $360\ifmmode^\circ\else\textdegree\fi{}$ wall is perturbed, it oscillates at a characteristic frequency in the gigahertz range which is tunable by the applied magnetic field, and an ac current applied at half the characteristic frequency excites a resonant response.

Despite the similarity of the broadband noise measured with a dc current in the two charge-density wave materials, NbSe 3 and o-TaS 3 , the noise measured with ac bias is very different. The memory function for the underlying configurational fluctuations in NbSe 3 is much more easily disrupted by bias switching, suggesting a different mechanism

We demonstrate the strong impact of the oscillator nonlinearity on the line broadening by studying spin-transfer-induced microwave emission in MgO-based tunnel junctions as a function of both the injected dc current and the temperature. In addition, we give clear evidences that the intrinsic noise is not dominated by thermal fluctuations but rather by the chaotization of the magnetic system induced by the spin transfer torque. A consequence is that the spectral linewidth is almost not reduced in decreasing the temperature.

Time-dependent electron-transport processes are often studied in the wide-band limit. In this paper, a generalized Floquet approach beyond the wide-band limit is developed for the general treatment of memory effect on the virtually unexplored multiphoton (MP) coherent destruction of tunneling (CDT) phenomenon of periodically driven electrode-wire-electrode nanoscale systems. As a case study, we apply the approach for a detailed analysis of the electron-transport dc current in the electrode-quantum double dot-electrode system, showing the significance of memory effect as well as illustrating the origin of the MP-CDT phenomenon.

We predict the current-induced formation of equilibrium phase textures for a multicomponent superconducting order parameter. Using the two-component Ginzburg-Landau and Usadel equations, we show that, for weakly coupled comoving superconducting condensates, the dc current $I$ first causes the breakdown of the phase-locked state at $Ig{I}_{c1}$ followed by the formation of intrinsic phase textures well below the depairing current ${I}_{d}$. These phase textures can manifest themselves in multilayer structures, atomic Bose condensate mixtures in optical lattices, and two-gap superconductors, particularly ${\mathrm{MgB}}_{2}$, where they can result in oscillating and resistive switching effects.

The shape of the V-I characteristics leading to a peak in the differential resistance r_d=dV/dI in the vicinity of the order-disorder transition in NbSe2 is investigated. r_d is large when measured by dc current. However, for a small Iac on a dc bias r_d decreases rapidly with frequency, even at a few Hz, and displays a large out-of-phase signal. In contrast, the ac response increases with frequency in the absence of dc bias. These surprisingly opposite phenomena and the peak in r_d are shown to result from a dynamic coexistence of two vortex matter phases rather than from the commonly assumed plastic depinning., Comment: 12 pages 4 figures. Accepted for publication in PRB rapid

The giant magnetoimpedance (GMI) effect in positive magnetostrictive glass-coated amorphous ${\mathrm{Co}}_{83.2}{\mathrm{Mn}}_{7.6}{\mathrm{Si}}_{5.8}{\mathrm{B}}_{3.3}$ microwire has been studied as a function of a dc magnetic field $\ensuremath{-}140l{H}_{\mathrm{dc}}l140\mathrm{Oe}$ and frequency $0.1lfl12.85\mathrm{MHz}.$ A maximum change of 43% in the MI of the as-quenched sample has been observed around 5 MHz frequency. Heat treatment of the sample by passing a dc current of 50 mA through it enhances the MI value to a large extent (maximum change \ensuremath{\sim}94%) by increasing the outer domain volume and inducing a transverse anisotropy. On the other hand, application of an external tensile stress reduces the GMI value by increasing the inner core domain and developing an axial anisotropy. In an as-quenched sample, the maximum value of MI is observed at ${H}_{\mathrm{dc}}\ensuremath{\sim}0$ when measured at frequency $fl8\mathrm{MHz}$ beyond which a two peak MI profile is seen. The heat-treated sample shows this two peak behavior from a much lower frequency (below 1 MHz) and additional peaks at ${H}_{\mathrm{dc}}\ensuremath{\sim}0$ for $fg10\mathrm{MHz}.$ Asymmetry in the MI peaks of a microwire has been produced by passing a dc current through the sample during impedance measurement. The magnetization of the as-quenched and heat-treated samples has also been studied to understand the domain structure and magnetoimpedance results.

A quantum-mechanical transport theory is developed to nonlinear electrical-transport phenomena in Hubbard chains. The intrasite Coulomb repulsion is assumed to be sufficiently strong, and the electron-transfer term is treated as a perturbation. The interaction between electrons and intrasite vibrations is taken into account by two types of coupling terms. The effects of the electron-phonon interaction and structural disorder are discussed. dc current peaks and negative resistance are found and explained by considering four possible carrier-transfer processes between sites. In disordered systems, new current peaks characterized by the disorder are also found.