Evidence of radiation-driven Landau states in 2D electron systems: magnetoresistance oscillations phase shift

We provide the ultimate explanation of one of the core features of microwave-induced magnetoresistance oscillations in high mobility two dimensional electron systems: the 1/4-cycle phase shift of minima. We start with the radiation-driven electron orbits model with the novel concept of scattering flight-time between Landau states. We calculate the extrema and nodes positions obtaining an exact coincidence with the experimental ones. The main finding is that the physical origin of the phase shift is a delay of $\frac{\pi}{2}$ of the radiation-driven Landau guiding center with respect to radiation, demonstrating the oscillating nature of the irradiated Landau states. We analyze the dependence of this minima on radiation frequency and power and its possible shift with the quality of the sampleComment: 5 pages, 3 figure

Resonance peak shift in the photo-current of ultrahigh-mobility two-dimensional electron systems

We report on a theoretical study on the rise of strong peaks at the harmonics of the cyclotron resonance in the irradiated magnetoresistance in ultraclean two-dimensional electron systems. The motivation is the experimental observation of a totally unexpected strong resistance peak showing up at the second harmonic. We extend the radiation-driven electron orbit model (previously developed to study photocurrent oscillations and zero resistance states) to a ultraclean scenario that implies longer scattering time and longer mean free path. Thus, when the mean free path is equivalent, in terms of energy, to twice the cyclotron energy ($2\hbar w_{c}$), the electron behaves as under an effective magnetic field twice the one really applied. Then, at high radiation power and/or low temperature, a resistance spike can be observed {\it at the second harmonic}. For even cleaner samples the energy distance could increase to three or four times the cyclotron energy giving rise to resistance peaks at higher harmonics (third, fourth, etc.), i.e., a resonance peak shift to lower magnetic fields as the quality of the sample increases. Thus, by selecting the sample mobility one automatically would select the radiation resonance response without altering the radiation frequency.Comment: Accepted in Physical Review B 6 pages, 5 figure

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.Comment: 8 pages,2 Postscript Figure

Effect of a in-plane magnetic field on the microwave assisted magnetotransport in a two-dimensional electron system

In this work we present a theoretical approach to study the effect of an in-plane (parallel) magnetic field on the microwave-assisted transport properties of a two-dimensional electron system. Previous experimental evidences show that microwave-induced resistance oscillations and zero resistance states are differently affected depending on the experimental set-up: two magnetic fields (two-axis magnet) or one tilted magnetic field. In the first case, experiments report a clear quenching of resistance oscillations and zero resistance states. In a tilted field, one obtains oscillations displacement and quenching but the latter is unbalanced and less intense. In our theoretical proposal we explain these results in terms of the microwave-driven harmonic motion performed by the electronic orbits and how this motion is increasingly damped by the in-plane field.Comment: Figure 1 has been change