arXiv subjects

Gloria Platero

Publications and source records attributed to Gloria Platero.

At least 109 records · Page 6Linked to original sources

arXiv2006

Magnetoresistivity Modulated Response in Bichromatic Microwave Irradiated Two Dimensional Electron Systems

We analyze the effect of bichromatic microwave irradiation on the magnetoresistivity of a two dimensional electron system. We follow the model of microwave driven Larmor orbits in a regime where two different microwave lights with different frequencies are illuminating the sample ($w_{1}$ and $w_{2}$). Our calculated results demonstrate that now the electronic orbit centers are driven by the superposition of two harmonic oscillatory movements with the frequencies of the microwave sources. As a result the magnetoresisitivity response presents modulated pulses in the amplitude with a frequency of $\frac{w_{1}-w_{2}}{2}$, whereas the main response oscillates with $\frac{w_{1}+w_{2}}{2}$.

cond-mat.mes-hall↗

arXiv2006

Spin filtering through excited states in double quantum dot pumps

Recently it has been shown that ac-driven double quantum dots can act as spin pumps and spin filters. By calculating the current through the system for each spin polarization, by means of the time evolution of the reduced density matrix in the sequential tunneling regime (Born-Markov approximation), we demonstrate that the spin polarization of the current can be controlled by tuning the parameters (amplitude and frequency) of the ac field. Importantly, the pumped current as a function of the applied frequency presents a series of peaks which are uniquely associated with a definite spin polarization. We discuss how excited states participating in the current allow the system to behave as a bipolar spin filter by tuning the ac frequency and intensity. We also discuss spin relaxation and decoherence effects in the pumped current and show that measuring the width of the current vs frequency peaks allows to determine the spin decoherence time $T_{2}$.

cond-mat.mes-hall↗

arXiv2005

Spin-dependent transport through magnetic nanojunctions

Coherent electronic transport through a molecular device is studied using non-equilibrium Green's function (NEGF) formalism. Such device is made of a carbon nanowire which is connected to ferromagnetic electrodes. The molecule itself is described with the help of Hubbard model (Coulomb interactions are treated by means of the Hartree-Fock approximation), while the coupling to the electrodes is modeled through the use of a broad-band theory. It was shown that magnetoresistance varies periodically with increasing the length of atomic wire (in the linear response regime) and oscillates with increasing of bias voltage (in the nonlinear response regime). Since the TMR effect for analyzed structures is predicted to be large (tens of percentage), considered junctions seem to be suitable for application as a magnetoresistive elements in the future electronic circuits.

cond-mat.mes-hall↗

arXiv2005

AC-driven double quantum dots as spin pumps and spin filters

We propose and analyze a new scheme of realizing both spin filtering and spin pumping by using ac-driven double quantum dots in the Coulomb blockade regime. By calculating the current through the system we demonstrate that the spin polarization of the current can be controlled by tuning the parameters (amplitude and frequency) of the ac field. We also discuss spin relaxation and decoherence effects in the pumped current.

cond-mat.mes-hall↗

arXiv2004

Theoretical approach to micro wave radiation-induced zero-resistance states in 2D electron systems

We present a theoretical model in which the existence of radiation-induced zero-resistance states is analyzed. An exact solution for the harmonic oscillator wave function in the presence of radiation, and a perturbation treatment for elastic scattering due to randomly distributed charged impurities, form the foundations of our model. Following this model most experimental results are reproduced, including the formation of resistivity oscillations, their dependence on the intensity and frequency of the radiation, temperature effects, and the locations of the resistivity minima. The existence of zero-resistance states is thus explained in terms of the interplay of the electron MW-driven orbit dynamics and the Pauli exclusion principle.

cond-mat.mes-hall↗

arXiv2003

Photon-assisted transport in semiconductor nanostructures

In this review we focus on electronic transport through semiconductor nanostructures which are driven by ac fields. Along the review we describe the available experimental information on different nanostructures, like resonant tunneling diodes, superlattices or quantum dots, together with the theoretical tools needed to describe the observed features. These theoretical tools such as, for instance, the Floquet formalism, the non-equilibrium Green's function technique or the density matrix technique, are suitable for tackling with photon-assisted transport problems where the interplay of different aspects like nonequilibrium, nonlinearity, quantum confinement or electron-electron interactions gives rise to many intriguing new phenomena. Along the review we give many examples which demonstrate the possibility of using appropriate ac fields to control/manipulate coherent quantum states in semiconductor nanostructures.

cond-mat.mes-hall↗

arXiv2002

Spin-polarized current oscillations in diluted magnetic semiconductor multiple quantum wells

We study the spin and charge dynamics of electrons in n-doped II--VI semiconductor multiple quantum wells when one or more quantum wells are doped with Mn. The interplay between strongly nonlinear inter-well charge transport and the large tunable spin-splitting induced by exchange interactions with spin-polarized Mn ions produces interesting new spin dependent features. The tunneling current between quantum wells can be strongly spin polarized and, under certain conditions, can develop self sustained oscillations under a finite dc voltage. The spin polarization oscillates in both magnetic and nonmagnetic quantum wells and the time average in magnetic wells can differ from its zero-voltage value. Our numerical simulations demonstrate that the amplitude of the spin polarization oscillations depends on the distribution of magnetic wells within the sample. We discuss how the spin polarized current and the spin polarization of the quantum wells can be tailored experimentally.

cond-mat↗

arXiv2001

Field-domain spintronics in magnetic semiconductor multiple quantum wells

We develop a theory of non-linear growth direction transport in magnetically doped II-VI compound semiconductor multiple-quantum-well systems. We find that the formation of electric field domains can be controlled by manipulating the space dependence of the band electron spin-polarization, using its exchange coupling to local moments. We emphasize the importance of band electron spin relaxation in limiting the strength of these effects.

cond-mat↗

arXiv2001

Photoassisted dynamical transport in multiple quantum wells

We study the dynamical transport in weakly coupled superlattices in the presence of intense radiation in the THz regime. We derive a general model for the time dependent tunneling current within the Keldysh nonequilibrium-Green-function formalism. For the particular situation in which fast scattering procceses drive the system to local equilibrium in the wells drastic changes are found in the current vs. voltage curves.

cond-mat↗

arXiv2001

Canted phase in double quantum dots

We perform a Hartree-Fock calculation in order to describe the ground state of a vertical double quantum dot in the absence of magnetic fields parallel to the growth direction. Intra- and interdot exchange interactions determine the singlet or triplet character of the system as the tunneling is tuned. At finite Zeeman splittings due to in-plane magnetic fields, we observe the continuous quantum phase transition from ferromagnetic to symmetric phase through a canted antiferromagnetic state. The latter is obtained even at zero Zeeman energy for an odd electron number.

cond-mat.mes-hall↗

arXiv2000

Low temperature transport in AC-driven Quantum Dots in the Kondo regime

We present a fully nonequilibrium calculation of the low temperature transport properties of a quantum dot in the Kondo regime when an AC potential is applied to the gate voltage. We solve a time dependent Anderson model with finite on-site Coulomb interaction. The interaction self-energy is calculated up to second order in perturbation theory in the on-site interaction, in the context of the Keldysh non-equilibrium technique, and the effect of the AC voltage is taken into account exactly for all ranges of AC frequencies and AC intensities. The obtained linear conductance and time-averaged density of states of the quantum dot evolve in a non trivial way as a function of the AC frequency and AC intensity of the harmonic modulation.

cond-mat.str-el↗

arXiv2000

Quasiperiodic time dependent current in driven superlattices: distorted Poincare maps and strange attractors

Intriguing routes to chaos have been experimentally observed in semiconductor superlattices driven by an ac field. In this work, a theoretical model of time dependent transport in ac driven superlattices is numerically solved. In agreement with experiments, distorted Poincare maps in the quasiperiodic regime are found. They indicate the appearance of very complex attractors and routes to chaos as the amplitude of the AC signal increases. Distorted maps are caused by the discrete well-to-well jump motion of a domain wall during spiky high-frequency self-sustained oscillations of the current.

cond-mat↗

arXiv1999

Current self-oscillations, spikes and crossover between charge monopole and dipole waves in semiconductor superlattices

Self-sustained current oscillations in weakly-coupled superlattices are studied by means of a self-consistent microscopic model of sequential tunneling including boundary conditions naturally. Well-to-well hopping and recycling of charge monopole domain walls produce current spikes (high frequency modulation) superimposed on the oscillation. For highly doped injecting contacts, the self-oscillations are due to dynamics of monopoles. As the contact doping decreases, a lower-frequency oscillatory mode due to recycling and motion of charge dipoles is predicted. For low contact doping, this mode dominates and monopole oscillations disappear. At intermediate doping, both oscillation modes coexist as stable solutions and hysteresis between them is possible.

cond-mat↗

arXiv1998

Kondo effect in AC transport through Quantum dots

A theory of the Kondo effect in quantum dots at zero temperature in the presence of arbitrary intense AC potentials is presented.We generalize the Friedel-Langreth sum rule to take care of charge conservation and propose a consistent procedure to study a time dependent Anderson Hamiltonian. The effect of the AC potential on both the quantum dot density of states and the linear conductance shows the importance of using a theory which describes intradot finite interaction and nonperturbative effects.

cond-mat.str-el↗

arXiv1997

Microscopic Model for Sequential Tunneling in Semiconductor Multiple Quantum Wells

We propose a selfconsistent microscopic model of vertical sequential tunneling through a multi-quantum well.The model includes a detailed description of the contacts,uses the Transfer Hamiltonian for expressions of the current and it treats the Coulomb interaction within a mean field approximation. We analyze the current density through a double well and a superlattice and study the formation of electric field domains and multistability coming from the Coulomb interaction. Phase diagrams of parameter regions (bias, doping in the heterostructure and in the contacts,etc) where the different solutions exist are given.

cond-mat↗

arXiv1997

Electron-Photon interaction in resonant tunneling diodes

We develope a model to describe the transmission coefficient and tunneling current in the presence of photon-electron coupling in a resonant diode. Our model takes into account multiphoton processes as well as the transitions between electronic states with different wave numbers. This is crutial to explain the experimental features observed in the tunneling current through a double barrier which cannot be reproduced with more simplified established models. According to our results, what experiments show in the current density are quantum photon-assisted features coming from multiphoton transitions which are not related with sample heating.

cond-mat↗

arXiv1996

Dynamical Localization and Absolute Negative Conductance in an ac driven double quantum well

We analyze the I-V characteristic of a double quantum well integrated in an antenna and driven by THz radiation.We propose a microscopic model to calculate the sequential current including selfconsistently the Coulomb interaction in a mean field approximation.Additional features in the current appear which depend not only on the frequency and intensity of the ac field but also on the charge in the wells.We observe,for some intensities and frequencies of the ac field,dynamical localization, i.e., quenching of the transmission,and, in the linear response regime, absolute negative conductance.We compare our calculations with recent experiments in driven double wells.

cond-mat↗

arXiv1995

Photoassisted sequential resonant tunneling through superlattices

We have analyzed theoretically the photoassisted tunneling current through a superlattice in the presence of an AC potential. For that purpose we have developed a new model to calculate the sequential resonant currrent trhough a superlattice based in the TRansfer Hamiltonian Method. The tunneling current presents new features due to new effective tunneling chanels coming from the photoside bands induced by the AC field. Our theoretical results are in good agreement with the available experimental evidence.

cond-mat↗