Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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6 records were found.
Spin and population dynamics of photoexcited carriers in GaAs/AlGaAs and InGaAs/InP quantum wells is investigated from 5K to 300K, revealing transition between excitonic and free carrier spin-relaxation at intermediate temperatures. Localisation is found to prolong spin relaxation of excitons by two orders of magnitude.
Spin and population dynamics of photoexcited carriers in GaAs/AlGaAs and InGaAs/InP quantum wells is investigated from 5K to 300K, revealing transition between excitonic and free carrier spin-relaxation at intermediate temperatures. Localisation is found to prolong spin relaxation of excitons by two orders of magnitude.
Optical spin-dynamic measurements in a high-mobility n-doped GaAs/AlGaAs quantum well show oscillatory evolution at 1.8 K consistent with a quasi-collision-free D’yakonov-Perel’-Kachorovskii regime. Above 5 K evolution becomes exponential as expected for collision-dominated spin dynamics. Momentum scattering times extracted from Hall mobility and Monte Carlo simulation of spin polarization agree at 1.8 K but diverge at higher temperatures, indicating the importance of electron-electron scattering and an intrinsic upper limit for the spin-relaxation rate.
We describe optical measurements of electron spin dynamics in a high-mobility n-doped GaAs/AlGaAs quantum well which test the customary assumptions of the D'yakonov, Perel’ and Kachorovskii mechanism of electron spin relaxation. At 1.8 K, spin evolution is oscillatory indicating breakdown of collision-dominated relaxation. At higher temperatures spin evolution is exponential but extracted scattering times deviate strongly from transport momentum relaxation times. This discrepancy can be ascribed to electron–electron scattering previously overlooked as a contributor to spin relaxation.
Room temperature picosecond pump-probe transmission measurements on InGaAsP/InGaAsP MQWs have shown large rotation (~40°) of probe polarisation induced by circularly polarised pump. We report low temperature investigations in a lattice matched In(.43)Ga(.57)As/InP MQW 8nm wide which does not reproduce this remarkable effect. Our measurements were made with an all-solid-state optical parametric oscillator tunable from 1.2 to 6µm. The non-linear crystal is periodically poled lithium niobate fabricated at Southampton, pumped synchronously by a modelocked, diode pumped Nd:YLF laser
Room temperature picosecond pump-probe transmission measurements on InGaAsP/InGaAsP MQWs have shown large rotation (~40°) of probe polarisation induced by circularly polarised pump and have been proposed as a mechanism for optical switching. We report low temperature investigations in a lattice matched 8nm.
