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The control and manipulation of filamentary resistive switching (FRS) is essential for practical applications in fields like non-volatile memories and neuromorphic computing. However, key aspects of the dynamics of conductive filament formation and their influence on device resistance remain incompletely understood. In this work we study FRS in binary oxides based memristors by investigating the dynamics of oxygen vacancies (OV) on a two dimensional lattice and their role in forming low-resistance paths that facilitate the transition between high and low global resistance states. We reveal that the mere formation of an OV percolation path is insufficient to induce a transition to a low-resistance state. Instead, an OV concentration exceeding a critical threshold across all sites in the filament is required to generate a low-resistivity conducting path. Furthermore, we simulate the impact of static defects -which block OV migration and would correspond to voids in real porous samples-, on filament formation. We show that there is a range of defect density values where OV percolate through the sample, leading to the formation of OV filaments, but conductive paths remain absent. Additionally, a small concentration of defects can reduce the final value of the low-resistance state, thereby increasing the ON-OFF ratio. These findings provide valuable insights into optimizing defective nanomaterials with memristive properties, which are crucial for advancing in-memory and neuromorphic computing technologies., Comment: 8 figures, 28 pages in preprint form

Ferroelectric memristors are intensively studied due to their potential implementation in data storage and processing devices. In this work we show that the memristive behavior of metal/ferroelectric oxide/metal devices relies on the competition of two effects: the modulation of metal/ferroelectric interface barriers by the switchable ferroelectric polarization and the electromigration of oxygen vacancies, with the depolarizing field playing a fundamental role in the latter. We simulate our experimental results with a phenomenological model that includes both effects and we reproduce several non-trivial features of the electrical response, including resistance relaxations observed after external poling. Besides providing insight into the underlying physics of these complex devices, our work suggests that it is possible to combine non-volatile and volatile resistive changes in single ferroelectric memristors, an issue that could be useful for the development of neuromorphic devices., Comment: 23 pages in preprint form, 5 figures

The development of novel devices for neuromorphic computing and non-traditional logic operations largely relies on the fabrication of well controlled memristive systems with functionalities beyond standard bipolar behavior and digital ON-OFF states. In the present work we demonstrate for Ta$_2$O$_5$-based devices that it is possible to selectively activate/deactivate two series memristive interfaces in order to obtain clockwise or counter-clockwise multilevel squared remanent resistance loops, just by controlling the (a)symmetry of the applied stimuli and independently of the nature of the used metallic electrodes. Based on our thorough characterization, analysis and modeling, we show that the physical origin of this electrical behavior relies on controlled oxygen vacancies electromigration between three different zones of the active Ta$_2$O$_{5-x}$ layer: a central -- bulk -- one and two quasi-symmetric interfaces with reduced TaO$_{2-h(y)}$ layers. Our devices fabrication process is rather simple as it implies the room temperature deposition of only one CMOS compatible oxide -- Ta-oxide -- and one metal, suggesting that it might be possible to take advantage of these properties at low cost and with easy scability. The tunable opposite remanent resistance loops circulations with multiple -- analogic -- intermediate stable states allows mimicking the adaptable synaptic weight of biological systems and presents potential for non-standard logic devices., Comment: 9 pages, 7 figures

We investigate the switching kinetics of oxygen vacancies (Ov) diffusion in LPCMO-Ag memristive interfaces by performing experiments on the temperature dependence of the high resistance (HR) state under thermal cycling. Experimental results are well reproduced by numerical simulations based on thermally activated Ov diffusion processes and fundamental assumptions relying on a recent model proposed to explain bipolar resistive switching in manganite- based cells. The confident values obtained for activation energies and diffusion coefficient associated to Ov dynamics, constitute a validation test for both model predictions and Ov diffusion mechanisms in memristive interfaces.

We study non-equilibrium electron transport through a quantum impurity coupled to metallic leads using the equation of motion technique at finite temperature T. Assuming that the interactions are taking place solely in the impurity and focusing in the infinite Hubbard limit, we compute the out of equilibrium density of states and the differential conductance G_2(T,V) to test several scaling laws. We find that G_2(T,V)/G_2(T,0) is a universal function of both eV/T_K and T/T_K, being T_K the Kondo temperature. The effect of an in plane magnetic field on the splitting of the zero bias anomaly in the differential conductance is also analyzed. For a Zeeman splitting \Delta, the computed differential conductance peak splitting depends only on \Delta/T_K, and for large fields approaches the value of 2\Delta . Besides the traditional two leads setup, we also consider other configurations that mimics recent experiments, namely, an impurity embedded in a mesoscopic wire and the presence of a third weakly coupled lead. In these cases, a double peak structure of the Kondo resonance is clearly obtained in the differential conductance while the amplitude of the highest peak is shown to decrease as \ln(eV/T_K). Several features of these results are in qualitative agreement with recent experimental observations reported on quantum dots., Comment: 9 pages, 7 figures

We investigate the spin accumulation effect in eccentric semiconductor multichannel rings with Rashba spin-orbit interaction and threaded by a magnetic flux. Due to the finite eccentricity, the spin polarization induced at the borders of the sample is anisotropic and exhibits different patterns and intensities at specific angular directions. This effect, reminiscent of the spin polarization drift induced by the application of an in plane electric field, could be used to manipulate and functionalize the spin polarization in electronic nanorings., Comment: 14 pages preprint form,5 figures

We investigate the behavior of the dc voltage drop in a periodically driven double barrier structure (DBS) sensed by voltages probes that are weakly coupled to the system. We find that the four terminal resistance $R_{4t}$ measured with the probes located outside the DBS results identical to the resistance measured in the same structure under a stationary bias voltage difference between left and right reservoirs. This result, valid beyond the adiabatic pumping regime, can be taken as an indication of the universal character of $R_{4t}$ as a measure of the resistive properties of a sample, irrespectively of the mechanism used to induce the transport., Comment: 4 pages, 3 figures

We investigate the dc response of a 1D disordered ring coupled to a reservoir and driven by a magnetic flux with a linear dependence on time. We identify two regimes: (i) A localized or large length L regime, characterized by a dc conductance, g_{dc}, whose probability distribution P(g_{dc}) is identical to the one exhibited by a 1D wire of the same length L and disorder strength placed in a Landauer setup. (ii) A "multifloquet" regime for small L and weak coupling to the reservoir, which exhibits large currents and conductances that can be g_{dc} > 1, in spite of the fact that the ring contains a single electronic transmission channel. The crossover length between the multifloquet to the single channel transport regime, L_c, is controlled by the coupling to the reservoir., Comment: 5 pages, 4 figures

We calculate the distribution of the conductance G in a one-dimensional disordered wire at finite temperature T and bias voltage V in a independent-electron picture and assuming full coherent transport. At high enough temperature and bias voltage, where several resonances of the system contribute to the conductance, the distribution P(G(T,V)) can be represented with good accuracy by autoconvolutions of the distribution of the conductance at zero temperature and zero bias voltage. The number of convolutions depends on T and V. In the regime of very low T and V, where only one resonance is relevant to G(T,V), the conductance distribution is analyzed by a resonant tunneling conductance model. Strong effects of finite T and V on the conductance distribution are observed and well described by our theoretical analysis, as we verify by performing a number of numerical simulations of a one-dimensional disordered wire at different temperatures, voltages, and lengths of the wire. Analytical estimates for the first moments of P(G(T,V)) at high temperature and bias voltage are also provided., Comment: 9 pages, 7 figures, Submitted to PRB

We show that a finite magnetic flux threading a multichannel semiconductor ring induces spin accumulation at the borders of the sample when the Rashba spin-orbit interaction is taken into account even in the absence of external electric fields., Comment: 5 pages, 4 figures

We study the edge states in a two dimensional electron gas with a transverse magnetic field and Rashba spin-orbit coupling. In the bulk, the interplay between the external field perpendicular to the gas plane and the spin-orbit coupling leads to two branches of states that, within the same energy window, have different cyclotron radii. For the edge states, surface reflection generates hybrid states with the two cyclotron radii. We analyze the spectrum and spin structure of these states and present a semiclassical picture of them., Comment: 7 pages, 8 figures

Here we report on several anomalies in quantum transport at the band center of a bipartite lattice with vacancies that are surely due to its chiral symmetry, namely: no weak localization effect shows up, and, when leads have a single channel the transmission is either one or zero. We propose that these are a consequence of both the chiral symmetry and the large number of states at the band center. The probability amplitude associated to the eigenstate that gives unit transmission ressembles a classical trajectory both with or without vacancies. The large number of states allows to build up trajectories that elude the blocking vacancies explaining the absence of weak localization., Comment: 5 pages, 5 figures

Finite size effects in the localization properties of disordered quantum wires are analyzed through conductance calculations. Disorder is induced by introducing vacancies at random positions in the wire and thus preserving the chiral symmetry. For quasi one-dimensional geometries and low concentration of vacancies, an exponential decay of the mean conductance with the wire length is obtained even at the center of the energy band. For wide wires, finite size effects cause the conductance to decay following a non-pure exponential law. We propose an analytical formula for the mean conductance that reproduces accurately the numerical data for both geometries. However, when the concentration of vacancies increases above a critical value, a transition towards the suppression of the conductance occurs. This is a signature of the presence of ultra-localized states trapped in finite regions of the sample., Comment: 5 figures, revtex4

The effect of disorder on confined metallic cavities with an Aharonov-Bohm flux line is addressed. We find that, even deep in the diffusive regime, large values of persistent currents may arise for a wide variety of geometries. We present numerical results supporting an anomalous scaling law of the average typical current $< I_{typ}>$ with the strength of disorder $w$, $< I_{typ}> \sim w^{- \gamma}$ with $\gamma < 2$. This is contrasted with previously reported results obtained for cylindrical samples where a scaling $< I_{typ}> \sim w^{-2}$ has been found. Possible links to, up to date, unexplained experimental data are finally discussed., Comment: 5 pages, 4 figures

New aspects of spectral fluctuations of (quantum) chaotic and diffusive systems are considered, namely autocorrelations of the spacing between consecutive levels or spacing autocovariances. They can be viewed as a discretized two point correlation function. Their behavior results from two different contributions. One corresponds to (universal) random matrix eigenvalue fluctuations, the other to diffusive or chaotic characteristics of the corresponding classical motion. A closed formula expressing spacing autocovariances in terms of classical dynamical zeta functions, including the Perron-Frobenius operator, is derived. It leads to a simple interpretation in terms of classical resonances. The theory is applied to zeros of the Riemann zeta function. A striking correspondence between the associated classical dynamical zeta functions and the Riemann zeta itself is found. This induces a resurgence phenomenon where the lowest Riemann zeros appear replicated an infinite number of times as resonances and sub-resonances in the spacing autocovariances. The theoretical results are confirmed by existing ``data''. The present work further extends the already well known semiclassical interpretation of properties of Riemann zeros., Comment: 28 pages, 6 figures, 1 table, To appear in the Gutzwiller Festschrift, a special Issue of Foundations of Physics

A quasi-one-dimensional quantum dot containing two interacting electrons is analyzed in search of signatures of chaos. The two-electron energy spectrum is obtained by diagonalization of the Hamiltonian including the exact Coulomb interaction. We find that the level-spacing fluctuations follow closely a Wigner-Dyson distribution, which indicates the emergence of quantum signatures of chaos due to the Coulomb interaction in an otherwise non-chaotic system. In general, the Poincar\'e maps of a classical analog of this quantum mechanical problem can exhibit a mixed classical dynamics. However, for the range of energies involved in the present system, the dynamics is strongly chaotic, aside from small regular regions. The system we study models a realistic semiconductor nanostructure, with electronic parameters typical of gallium arsenide., Comment: 4 pages, 3ps figures

Confinement and surface roughness (SR) effects on the magnitude of the persistent current are analized for ballistic bidimensional metallic samples. Depending on the particular geometry, localized border states can show up at half filling. These border states contribute coherently to the persistent current and its magnitude is enhanced with respect to their value in the absent of confinement. A linear scaling of the typical current $I_{typ}$ with the number of conduction channels M is obtained. This result is robust with respect to changes in the relevant lengths of the samples and to the SR. Possible links of our results to experiments are also discussed., Comment: 5 pages, 6 figures

We consider a bidimensional discrete annular cavity with surface roughness (SR) threaded by a magnetic flux. In the ballistic regime and at half filling, localized border-states show up. These border states contribute coherentely to the persistent current and the magnitude of the typical current $I_{typ}$ is enhaced with respect to their value in the absence of confinement. This result is robust with respect to changes in the relevant lengths of the sample., Comment: 6 pages, 3 ps figures included

In the present article we perform analytical and numerical calculations related to persistent currents in 2D isolated mesoscopic annular cavities threaded by a magnetic flux. The system considered has a high number of open channels and therefore the single particle spectrum exhibits many level crossings as the flux varies. We determine the effect of the distribution of level crossings in the typical persistent current., Comment: 23 pages, including 6 figures

We consider a single particle spectrum as given by the eigenvalues of the Wigner-Dyson ensembles of random matrices, and fill consecutive single particle levels with n fermions. Assuming that the fermions are non-interacting, we show that the distribution of the total energy is Gaussian and its variance grows as n^2 log n in the large-n limit. Next to leading order corrections are computed. Some related quantities are discussed, in particular the nearest neighbor spacing autocorrelation function. Canonical and gran canonical approaches are considered and compared in detail. A semiclassical formula describing, as a function of n, a non-universal behavior of the variance of the total energy starting at a critical number of particles is also obtained. It is illustrated with the particular case of single particle energies given by the imaginary part of the zeros of the Riemann zeta function on the critical line., Comment: 28 pages in Latex format, 5 figures, submitted for publication to Physica D