arXiv subjects

G. Platero

Publications and source records attributed to G. Platero.

35 records · Page 2Linked to original sources

arXiv2008

Tunnel spectroscopy in ac-driven quantum dot nanoresonators

Electronic transport in a triple quantum dot shuttle device in the presence of an ac field is analyzed within a fully quantum mechanical framework. A generalized density matrix formalism is used to describe the time evolution for electronic state occupations in a dissipative phonon bath. In the presence of an ac gate voltage, the electronic states are dressed by photons and the interplay between photon and vibrational sidebands produces current characteristics that obey selection rules. Varying the ac parameters allows to tune the tunneling current features. In particular, we show that coherent destruction of tunneling can be achieved in our device.

cond-mat.other↗

arXiv2007

Hysteretic behavior in weakly coupled double-dot transport in the spin blockade regime

Double quantum dot systems in the spin blockade regime exhibit leakage currents that have been attributed to the Hyperfine interaction. We model weakly coupled double-dot transport using a rate equation approach which accounts for Hyperfine flip-flop transitions. The rate equations allow us to obtain self-consistently the time evolution for electronic charge occupations and for the nuclei polarizations in each dot. We analyze the current in the spin blockade region as a function of magnetic field and observe hysteretic behavior for fields corresponding to the crossing between triplet and singlet states.

cond-mat.mes-hall↗

arXiv2007

Multiquantum well spin oscillator

A dc voltage biased II-VI semiconductor multiquantum well structure attached to normal contacts exhibits self-sustained spin-polarized current oscillations if one or more of its wells are doped with Mn. Without magnetic impurities, the only configurations appearing in these structures are stationary. Analysis and numerical solution of a nonlinear spin transport model yield the minimal number of wells (four) and the ranges of doping density and spin splitting needed to find oscillations.

cond-mat.mes-hall↗

arXiv2006

Removing spin blockade by photon-assisted tunneling in double quantum dots

Pauli exclusion principle can lead to a supression of transport through double quantum dots, even if both quantum dots are connected by a resonant driving ac field. In this work, we study how this effect, known as spin blockade, can be removed by means of the influence of the driving field on the contacts to the leads.

cond-mat.mes-hall↗

arXiv2006

From zero resistance states to absolute negative conductivity in microwave irradiated 2D electron systems

Recent experimental results regarding a 2D electron gas subjected to microwave radiation reveal that magnetoresistivity, apart from presenting oscillations and zero resistance states, can evolve to negative values at minima. In other words, the current can evolve from flowing with no dissipation, to flow in the opposite direction of the dc bias applied. Here we present a theoretical model in which the existence of radiation-induced absolute negative conductivity is analyzed. Our model explains the transition from zero resistance states to absolute negative conductivity in terms of multiphoton assisted electron scattering due to charged impurities. It shows as well, how this transition can be driven by tuning microwave frequency and intensity. Then it opens the possibility of controlling the electron Larmor orbits dynamics (magnetoconductivity) in microwave driven nanodevices. The analysis of zero resistance states is therefore promising because new optical and transport properties in nanodevices will be expected.

cond-mat.mes-hall↗

arXiv2005

Temperature effects on microwave-induced resistivity oscillations and zero resistance states in 2D electron systems

In this work we address theoretically a key issue concerning microwave-induced longitudinal resistivity oscillations and zero resistance states, as is tempoerature. In order to explain the strong temperature dependence of the longitudinal resistivity and the thermally activated transport in 2DEG, we have developed a microscopic model based on the damping suffered by the microwave-driven electronic orbit dynamics by interactions with the lattice ions yielding acoustic phonons. Recent experimental results show a reduction in the amplitude of the longitudinal resistivity oscillations and a breakdown of zero resistance states as the radiation intensity increases. In order to explain it we have included in our model the electron heating due to large microwave intensities and its effect on the longitudinal resistivity.

cond-mat.mes-hall↗

arXiv2004

Charge Transport Through Open, Driven Two-Level Systems with Dissipation

We derive a Floquet-like formalism to calculate the stationary average current through an AC driven double quantum dot in presence of dissipation. The method allows us to take into account arbitrary coupling strengths both of a time-dependent field and a bosonic environment. We numerical evaluate a truncation scheme and compare with analytical, perturbative results such as the Tien-Gordon formula.

cond-mat.mes-hall↗

arXiv2004

Localization of interacting electrons in quantum dot arrays driven by an ac-field

We investigate the dynamics of two interacting electrons moving in a one-dimensional array of quantum dots under the influence of an ac-field. We show that the system exhibits two distinct regimes of behavior, depending on the ratio of the strength of the driving field to the inter-electron Coulomb repulsion. When the ac-field dominates, an effect termed coherent destruction of tunneling occurs at certain frequencies, in which transport along the array is suppressed. In the other, weak-driving, regime we find the surprising result that the two electrons can bind into a single composite particle -- despite the strong Coulomb repulsion between them -- which can then be controlled by the ac-field in an analogous way. We show how calculation of the Floquet quasienergies of the system explains these results, and thus how ac-fields can be used to control the localization of interacting electron systems.

cond-mat.mes-hall↗

arXiv2002

Electron Dynamics in AC-Driven Quantum Dots

We investigate the dynamics of interacting electrons confined to two types of quantum dot system, when driven by an external AC field. We first consider a system of two electrons confined to a pair of coupled quantum dots by using an effective two-site model of Hubbard-type. Numerically integrating the Schroedinger equation in time reveals that for certain values of the strength and frequency of the field the tunneling between the dots can be destroyed, thus allowing the correlated two-electron states to be manipulated. We then show how Floquet theory can be used to predict the field parameters at which this effect occurs. We then consider the case of confining the electrons to a single two-dimensional quantum dot in the limit of low particle-density. In this system the electrons form strongly correlated states termed Wigner molecules, in which the Coulomb interaction causes them to become highly localised in space. Again using an effective model of Hubbard-type, we investigate how the AC field can drive the dynamics of the Wigner states. As before, we find that the AC field can be used to control the tunneling between various charge configurations, and we relate this to the presence of avoided crossings in the Floquet quasi-energy spectrum. These results hold out the exciting possibility of using AC fields to control the time evolution of entangled states in mesoscopic devices, which has great relevance to the rapidly advancing field of quantum information processing.

cond-mat.mes-hall↗

arXiv2002

Dynamical control of correlated states in a square quantum dot

In the limit of low particle density, electrons confined to a quantum dot form strongly correlated states termed Wigner molecules, in which the Coulomb interaction causes the electrons to become highly localized in space. By using an effective model of Hubbard-type to describe these states, we investigate how an oscillatory electric field can drive the dynamics of a two-electron Wigner molecule held in a square quantum dot. We find that, for certain combinations of frequency and strength of the applied field, the tunneling between various charge configurations can be strongly quenched, and we relate this phenomenon to the presence of anti-crossings in the Floquet quasi-energy spectrum. We further obtain simple analytic expressions for the location of these anti-crossings, which allows the effective parameters for a given quantum dot to be directly measured in experiment, and suggests the exciting possibility of using ac-fields to control the time evolution of entangled states in mesoscopic devices.

cond-mat.mes-hall↗

arXiv2001

Coherent transport in a two-electron quantum dot molecule

We investigate the dynamics of two interacting electrons confined to a pair of coupled quantum dots driven by an external AC field. By numerically integrating the two-electron Schroedinger equation in time, we find that for certain values of the strength and frequency of the AC field we can cause the electrons to be localised within the same dot, in spite of the Coulomb repulsion between them. Reducing the system to an effective two-site model of Hubbard type and applying Floquet theory leads to a detailed understanding of this effect. This demonstrates the possibility of using appropriate AC fields to manipulate entangled states in mesoscopic devices on extremely short timescales, which is an essential component of practical schemes for quantum information processing.

cond-mat.mes-hall↗

arXiv2001

Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices

We examine how the current--voltage characteristics of a doped weakly coupled superlattice depends on temperature. The drift velocity of a discrete drift model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated as a function of temperature. Numerical simulations and theoretical arguments show that increasing temperature favors the appearance of current self-oscillations at the expense of static electric field domain formation. Our findings agree with available experimental evidence.

cond-mat↗

arXiv2000

Microscopic derivation of transport coefficients and boundary conditions in discrete drift-diffusion models of weakly coupled superlattices

A discrete drift-diffusion model is derived from a microscopic sequential tunneling model of charge transport in weakly coupled superlattices provided temperatures are low or high enough. Realistic transport coefficients and novel contact current--field characteristic curves are calculated from microscopic expressions, knowing the design parameters of the superlattice. Boundary conditions clarify when possible self-sustained oscillations of the current are due to monopole or dipole recycling.

cond-mat↗

arXiv1998

Magnetic Field Induced Charge Instabilities in Weakly Coupled Superlattices

Using a time dependent selfconsistent model for vertical sequential tunneling,we study the appearance of charge instabilities that lead to the formation of electric field domains in a weakly coupled doped superlattice in the presence of high magnetic fields parallel to the transport direction. The interplay between the high non linearity of the system --coming from the Coulomb interaction-- and the inter-Landau-level scattering at the domain walls (regions of charge accumulation inside the superlattice) gives rise to new unstable negative differential conductance regions and extra stable branches in the sawtooth-like I-V curves.

cond-mat↗

arXiv1997

Photon Assisted Electric Field Domains in Semiconductor Doped Superlattices

We study photon-assisted tunneling (PAT) through weakly-coupled doped semiconductor superlattices (SL's) in the high voltage regime. A self-consistent model which treats the Coulomb interaction in a mean field approximation is considered. We discuss the formation of electric field domains in the presence of THz radiation and the appearance of new multistability regions caused by the combined effect of the strong non linearity coming from the Coulomb interaction and the new PAT channels.We show how the electric field domains can be supported by the virtual photonic sidebands due to multiple photon emission and absorption.

cond-mat↗

arXiv1996

Coherent resonant tunneling in ac fields

We have analyzed the tunneling transmission probability and electronic current density through resonant heterostructures in the presence of an external electromagnetic field. In this work, we compare two different models for a double barrier : In the first case the effect of the external field is taken into account by spatially dependent AC voltages and in the second one the electromagnetic field is described in terms of a photon field that irradiates homogeneously the whole sample. While in the first description the tunneling takes place mainly through photo sidebands in the case of homogeneous illumination the main effective tunneling channels correspond to the coupling between different electronic states due to photon absorption and emission. The difference of tunneling mechanisms between these configurations is strongly reflected in the transmission and current density which present very different features in both cases. In order to analyze these effects we have obtained, within the Transfer Hamiltonian framework, a general expression for the transition probability for coherent resonant tunneling in terms of the Green's function of the system.

cond-mat↗

arXiv1994

Coherent and sequential photoassisted tunneling through a semiconductor double barrier structure

We have studied the problem of coherent and sequential tunneling through a double barrier structure, assisted by light considered to be present All over the structure, i,e emitter, well and collector as in the experimental evidence. By means of a canonical transformation and in the framework of the time dependent perturbation theory, we have calculated the transmission coefficient and the electronic resonant current. Our calculations have been compared with experimental results turning out to be in good agreement. Also the effect on the coherent tunneling of a magnetic field parallel to the current in the presence of light, has been considered.

cond-mat↗