Theory of light-induced current in molecular-tunneling junctions excited with intense shaped pulses

A theory for light-induced current by strong optical pulses in molecular-tunneling junctions is described. We consider a molecular bridge represented by its highest occupied and lowest unoccupied levels, HOMO and LUMO, respectively. We take into account two types of couplings between the molecule and the metal leads: electron transfer that gives rise to net current in the biased junction and energy transfer between the molecule and electron-hole excitations in the leads. Using a Markovian approximation, we derive a closed system of equations for the expectation values of the relevant variables: populations and molecular polarization that are binary, and exciton populations that are tetradic in the annihilation and creation operators for electrons in the molecular states. We have proposed an optical control method using chirped pulses for enhancing charge transfer in unbiased junctions where the bridging molecule is characterized by a strong charge-transfer transition. An approximate analytical solution of the resulting dynamical equation is supported by a full numerical solution. When energy transfer between the molecule and electron-hole excitations in the leads is absent, the optical control problem for inducing charge transfer with linearly chirped pulse can be reduced to the Landau-Zener transition to a decaying level. When chirp is fast with respect to the rate of the electron transfer, the Landau theory is recovered. The proposed control mechanism is potentially useful for developing novel opto-electronic single-electron devices with optical gating based on molecular nanojunctions.Comment: 14 pages, 7 figures; submitted to PR

Electron Transport in Double Quantum Dot governed by Nuclear Magnetic Field

We investigate theoretically electron transfer in a doble dot in a situation where it is governed by nuclear magnetic field: This has been recently achieved in experiment. We show how to partially compensate the nuclear magnetic field to restore Spin Blockade

Efficient Magnetization Reversal with Noisy Currents

We propose to accelerate reversal of the ferromagnetic order parameter in spin valves by electronic noise. By solving the stochastic equations of motion we show that the current-induced magnetization switching time is drastically reduced by a modest level of externally generated current (voltage) noise. This also leads to a significantly lower power consumption for the switching process.Comment: 4 pages, 3 figure

Lineamientos de política pública para el sector de agua potable y saneamiento

Incluye bibliografíaUna versión preliminar del presente documento fue presentada y debatida en la Conferencia Regional "Construyendo Compromiso, Eficiencia y Equidad para Servicios Sustentables de Agua Potable y Saneamiento en América Latina y el Caribe" (Sede de la CEPAL, Santiago de Chile, 15 y 16 de marzo de 2011) (véase el anexo 2)Este documento sintetiza -en forma de lineamientos de políticas públicas para el sector de agua potable y saneamiento- la experiencia acumulada en el desarrollo de las actividades de investigación y asistencia técnica (véase el anexo 1); realizadas en el marco del proyecto "Sustentabilidad y la igualdad de oportunidades en globalización. Componente 1, Tema 4: Construyendo Compromiso, Eficiencia y Equidad para Servicios Sustentables de Agua Potable y Saneamiento en América Latina y el Caribe", cuyo objetivo fue fortalecer la capacidad de los gobiernos de los países de la región para diseñar e implementar políticas públicas efectivas con énfasis en compromiso, eficiencia, equidad y sostenibilidad. Las lecciones se agrupan en las siguientes ocho líneas de análisis: i); factores exógenos determinantes del desempeño y la sustentabilidad de la prestación de los servicios; ii); eficiencia en organismos prestadores; iii); organización institucional del sector; iv); estructura industrial; v); regulación y contratos; vi); tarifas y subsidios; vii); políticas para población rural; y viii); nuevas condicionantes que impone la globalización. Una versión preliminar del presente documento fue presentada y debatida en la Conferencia Regional "Construyendo Compromiso, Eficiencia y Equidad para Servicios Sustentables de Agua Potable y Saneamiento en América Latina y el Caribe" (Sede de la CEPAL, Santiago de Chile, 15 y 16 de marzo de 2011); (véase el anexo 2);. Este documento ha sido eleborado en el marco del proyecto "Sustentabilidad e igualdad de oportunidades en globalización. Componente 1, Tema 4: Construyendo compromiso, eficiencia y equidad para servicios sustentables de agua potable y saneamiento en América Latina y el Caribe" (GER 08/004);, ejecutado por la Comisión Económica para América Latina y el Caribe (CEPAL); en conjunto con la Cooperación Técnica Alemana (GTZ); y financiado por el Ministerio Federal de Cooperación Económica y Desarrollo de Alemania (BMZ);, y la cooperación del proyecto "Gestión sostenible de los recursos naturales y de las infraestructuras" (FRA/09/002);, ejecutado por la CEPAL en conjunto con el Ministerio de Asuntos Exteriores de Francia

Shot Noise in Mesoscopic Transport Through Localised States

We show that shot noise can be used for studies of hopping and resonant tunnelling between localised electron states. In hopping via several states, shot noise is seen to be suppressed compared with its classical Poisson value $S_I=2eI$ ($I$ is the average current) and the suppression depends on the distribution of the barriers between the localised states. In resonant tunnelling through a single impurity an enhancement of shot noise is observed. It has been established, both theoretically and experimentally, that a considerable increase of noise occurs due to Coulomb interaction between two resonant tunnelling channels.Comment: 7 pages, 5 figures; Proceedings of the 10th Conference on Hopping and Related Phenomena (Trieste 2003); requires Wiley style files (included

Magnetic field induced effects in the high source-drain bias current of weakly coupled vertical quantum dot molecules

We report on the basic properties of recently observed magnetic field resonance, induced time dependent oscillation, and hysteresis effects in the current flowing through two weakly coupled vertical quantum dots at high source-drain bias (up to a few tens of mV). These effects bare some similarity to those reported in the N=2 spin-blockade regime, usually for weak in-plane magnetic field, of quantum dot molecules and attributed to hyperfine coupling, except here the measurements are conducted outside of the spin-blockade regime and the out-of-plane magnetic field is up to ~6 T.Comment: 3 pages, 3 figures, accepted for publication in Physica E in EP2DS 17 conference proceeding

Statistics of Transmission Eigenvalues for a Disordered Quantum Point Contact

We study the distribution of transmission eigenvalues of a quantum point contact with nearby impurities. In the semi-classical case (the chemical potential lies at the conductance plateau) we find that the transmission properties of this system are obtained from the ensemble of Gaussian random reflection matrices. The distribution only depends on the number of open transport channels and the average reflection eigenvalue and crosses over from the Poissonian for one open channel to the form predicted by the circuit theory in the limit of large number of open channels.Comment: 8 pages, 3 figure

Enhanced shot noise in resonant tunnelling via interacting localised states

In a variety of mesoscopic systems shot noise is seen to be suppressed in comparison with its Poisson value. In this work we observe a considerable enhancement of shot noise in the case of resonant tunnelling via localised states. We present a model of correlated transport through two localised states which provides both a qualitative and quantitative description of this effect.Comment: 4 pages, 4 figure