RESUMO
A gallium interstitial defect is thought to be responsible for the spectacular spin-dependent recombination in GaAs_{1-x}N_{x} dilute nitrides. Current understanding associates this defect with at least two in-gap levels corresponding to the (+/0) and (++/+) charge-state transitions. Using a spin-sensitive photoinduced current transient spectroscopy, the in-gap electronic structure of a x=0.021 alloy is revealed. The (+/0) state lies ≈0.27 eV below the conduction band edge, and an anomalous, negative activation energy reveals the presence of not one but two other in-gap states. The observations are consistent with a (++/+) state ≈0.19 eV above the valence band edge, and a (+++/++) state ≈25 meV above the valence band edge.
RESUMO
The ability to measure nanoradian polarization rotations, θF, in the photon shot noise limit is investigated for partially crossed polarizers (PCP), a static Sagnac interferometer, and an optical bridge, each of which can in principle be used in this limit with near equivalent figures-of-merit (FOM). In practice a bridge to PCP/Sagnac source noise rejection ratio of 1/4θF2 enables the bridge to operate in the photon shot noise limit even at high light intensities. The superior performance of the bridge is illustrated via the measurement of a 3 nrad rotation arising from an axial magnetic field of 0.9 nT applied to a terbium gallium garnet. While the Sagnac is functionally equivalent to the PCP in terms of the FOM, unlike the PCP it is able to discriminate between rotations with different time (T) and parity (P) symmetries. The Sagnac geometry implemented here is similar to that used elsewhere to detect non-reciprocal (T¯P) rotations like those due to the Faraday effect. Using a Jones' matrix approach, novel Sagnac geometries uniquely sensitive to non-reciprocal TP¯ (e.g. magneto-electric or magneto-chiral) rotations, as well as to reciprocal rotations (e.g. due to linear birefringence, TP, or to chirality, TP¯) are proposed.
RESUMO
Photoinduced matter motion in thin films containing azobenzene derivatives grafted to a polymer backbone is investigated by means of near-field probe microscopy. We evidence the existence of two different photomechanical processes which produce mass transport. One is governed by the light intensity pattern and the other by the light polarization pattern. The intensity-driven mechanism is found to critically depend on the polymer matrix while the polarization-driven mechanism occurs with almost the same efficiency in different materials. Depending on the relationship between the polarization and intensity patterns, the two processes may either compete or cooperate giving rise to a nontrivial directional mass transport process.
RESUMO
An asymmetrical ferromagnetic cobalt bilayer (18 nm Au/0.8 nm Co/2.2 nm Au/1.3 nm Co/1.5 nm Au) operates as a self-calibrated spin polarimeter with a high spin selectivity for free electrons injected at a few eV above the Fermi level. We present the analysis of transmitted currents as a function of the incident energy, based on a model of spin polarization dilution into the first gold layer and ballistic transport close to the vacuum level throughout the sample.
