We investigate the effect of the oft-neglected cubic terms of the Dresselhaus spin-orbit coupling on the longitudinal current response of a two-dimensional electron gas with both Rashba and linear Dresselhaus interactions. Changes caused by these nonlinear-in-momentum terms on the absorption spectrum becomes more notable under SU(2) symmetry conditions, when the Rashba and linear Dresselhaus coupling strengths are tuned to be equal. The longitudinal optical response no longer vanishes then and shows a strong dependence on the direction of the externally applied electric field, giving a signature of the relative size of the several spin-orbits contributions. This anisotropic response arises from the non isotropic splitting of the spin states induced by the interplay of Rashba and Dresselhaus couplings. However, the presence of the cubic terms introduces characteristic spectral features and can modify the overall shape of the spectra for some values of the relative sizes of the spin-orbit parameters. In addition to the control through the driven frequency or electrical gating, this directional aspect of the current response suggests new ways of manipulation and supports the use of interband optics as a sensitive probe of spin-orbit mechanisms in semiconductor spintronics.
Ag and Cu nanoparticles supported in mordenite structure have been formed applying reduction temperatures in the range 100-400 C and varying Ag/Cu atomic ratios. Absorbance spectra of samples exhibit signature features consistent with absorption via localized surface plasmons propagating in metallic nanoparticles. The formation of binary Ag-Cu nanoparticles is inferred. Theoretical calculations within an average field Maxwell-Garnett model modified for a three component composite system are used to interpret resonance shifts and relative intensities of plasmon peaks in the experimental findings. Within the applied model the relative volume occupied by each metallic species can be changed. This permits the simulation of experimental conditions of the samples. It is experimentally found that the simultaneous presence of two metal species during the synthesis affects reduction temperatures, stability and relative concentration of embedded nanoparticles. Furthermore the observed optical spectra of the supported bimetallic nanoparticles is contrasted with that of single metal nanoparticles studied previously. Our study represents a contribution to the possibility of optical monitoring of synthetic pathways in zeolite + metal nanoparticle systems.
We investigate the dielectric response, the optical conductivity, and the plasmon spectrum of a two-dimensional electron gas with Rashba and Dresselhaus spin–orbit (SO) interaction. Using the self-consistent field approach, we derive expressions for the dispersion relations of the intra- and inter-SO plasmons. We found that the latter is immersed within the continuum of inter-SO single-particle excitations. The intra-SO plasmons remain undamped and almost unaffected by the SO coupling. The longitudinal optical conductivity shows, however, a dependence on the direction of the externally applied potential, caused by the anisotropic splitting of the spin states. In addition to the control through the driving frequency or electrical gating, this new aspect of the optical absorption spectrum might be useful in spintronics applications.
We investigate the optical conductivity and plasmon spectrum of a two-dimensional electron gas with Rashba and
Dresselhaus spin-orbit interaction. Using the self-consistent field approach we derive expressions for the dispersion
relations of the intra- and inter-SO plasmons. We found that the latter are immersed within the continuum of
inter-SO single-particle excitations. The intra-SO plasmons remain undamped and almost unaffected by the
spin-orbit coupling. Remarkably, the optical conductivity shows however a dependence on the direction of the
externally applied electric field, caused by the anisotropic splitting of the spin states. In addition to the control
through the driving frequency or electrical gating, this new aspect of the optical absorption spectrum might be
useful in spintronics applications.
Optical spectra of noble metal nano-particles supported on different types of zeolites are studied and compared. The absorbance spectra of Cu, Ag and Au nanoparticles supported on mordenite, β-zeolite, Na/Y and H/Y zeolites respectively are reported. Spectra for pre-exchanged Au-Cu/Na/Y, Au-Ni/Na/Y and Au-Fe/Na/Y are also studied. A simple effective medium approach (Maxwell-Garnett) is used to obtain a theoretical complex effective dielectric function of the composite and to asses the sensibility of the plasmon resonance to the sample characteristics. The knowledge of these properties can hopefully be applied to the development of optical tools to monitor the synthetic path.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Near field, Microscopes, Polarization, Nonlinear optics, Second-harmonic generation, 3D image processing, Image resolution, Scanning tunneling microscopy
Existing optical scanning microscopes don't allow the determination of the depth below the surface of the sample under which where scatterers might be located, due to the simple exponential decay of their evanescent probing field. We propose a nonlinear near field microscope which would allow three dimensional images of buried structures with nanometric resolution along all dimensions.
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