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.Comment: 5 pages and 4 figure

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 $\frac{w_{1}+w_{2}}{2}$.Comment: 4 pages, 3 figures Accepted in Applied Physics Letter

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.Comment: 4 pages and 4 figures. Accepted in Phys Rev

Microwave-induced resistance oscillations and zero-resistance states in 2D electron systems with two occupied subbands

We report on theoretical studies of recently discovered microwave-induced resistance oscillations and zero resistance states in Hall bars with two occupied subbands. In the same results, resistance presents a peculiar shape which appears to have a built-in interference effect not observed before. We apply the microwave-driven electron orbit model, which implies a radiation-driven oscillation of the two-dimensional electron system. Thus, we calculate different intra and inter-subband electron scattering rates and times that are revealing as different microwave-driven oscillations frequencies for the two electronic subbands. Through scattering, these subband-dependent oscillation motions interfere giving rise to a striking resistance profile. We also study the dependence of irradiated magnetoresistance with power and temperature. Calculated results are in good agreement with experiments.Comment: 7 pages, 6 figure

Dynamical nuclear spin polarization induced by electronic current through double quantum dots

We analyze electron spin relaxation in electronic transport through coherently coupled double quantum dots in the spin blockade regime. In particular, we focus on hyperfine interaction as the spin relaxation mechanism. We pay special attention to the effect of the dynamical nuclear spin polarization induced by the electronic current on the nuclear environment. We discuss the behaviour of the electronic current and the induced nuclear spin polarization versus an external magnetic field for different hyperfine coupling intensities and interdot tunnelling strengths. We take into account, for each magnetic field, all hyperfine mediated spin relaxation processes coming from the different opposite spin levels approaches. We find that the current as a function of the external magnetic field shows a peak or a dip, and that the transition from a current dip to a current peak behaviour is obtained by decreasing the hyperfine coupling or by increasing the interdot tunnelling strength. We give a physical picture in terms of the interplay between the electrons tunnelling out of the double quantum dot and the spin flip processes due to the nuclear environment.Comment: 25 pages and 8 figures. To be published in New Journal of Physic

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.Comment: Revtex 3.0 4 pages, 4 figures uuencoded compressed tar-fil