Magnetotransport in two-dimensional electron gas at large filling factors

We derive the quantum Boltzmann equation for the two-dimensional electron gas in a magnetic field such that the filling factor $\nu \gg 1$. This equation describes all of the effects of the external fields on the impurity collision integral including Shubnikov-de Haas oscillations, smooth part of the magnetoresistance, and non-linear transport. Furthemore, we obtain quantitative results for the effect of the external microwave radiation on the linear and non-linear $dc$ transport in the system. Our findings are relevant for the description of the oscillating resistivity discovered by Zudov {\em et al.}, zero-resistance state discovered by Mani {\em et al.} and Zudov {\em et al.}, and for the microscopic justification of the model of Andreev {\em et al.}. We also present semiclassical picture for the qualitative consideration of the effects of the applied field on the collision integral.Comment: 28 pages, 19 figures; The discussion of the role of the effect of the microwave field on the distribution function is revised (see also cond-mat/0310668). Accepted in Phys. Rev.

ELECTRICAL INSTABILITY IN RUBY UNDER OPTICAL PUMPING

The new phenomenon consists in a spontaneous appearance in strongly excited concentrated ruby of domains with strong (~ MV/cm) electric fields of opposite sign which persist for a long time after the termination of pumping. The photoinduced formation of domains was found to depend critically on external conditions (temperature, external electric field, pumping rate and wavelength of optical excitation), as well as on the chromium concentration. Photocurrent measurements support the phenomenological interpretation of the phenomenon as a result of an electrical instability caused by the negative, absolute and differential, conductivity of concentrated ruby under optical excitation

Temperature dependent spectroscopic studies of the electron delocalization dynamics of excited Ce ions in the wide band gap insulator, Lu2SiO5

Electron delocalization processes of optically excited states of Ce3+ impurities in Lu2SiO5 were investigated by means of a temperature and spectrally resolved photoconductivity study. By monitoring separately the strength of the photocurrent resulting from excitation into each of the Ce3+?5d absorption bands, over a broad temperature region, three different delocalization processes, namely direct photoionization, thermal ionization, and tunneling, have been identified. The relative probabilities and temperature dependencies of each of these processes are discussed. The observed exponential temperature increase in the photocurrent, which spans six orders of magnitude, allows for the exact placement of the lowest energy 5d levels of the Ce3+ ions within the band gap. For Lu2SiO5:Ce3+, the lowest 5d state is determined to be 0.45 eV below the conduction band edge.Radiation, Radionuclides and ReactorsApplied Science