6,047 research outputs found
Nonequilibrium nuclear-electron spin dynamics in semiconductor quantum dots
We study the spin dynamics in charged quantum dots in the situation where the
resident electron is coupled to only about 200 nuclear spins and where the
electron spin splitting induced by the Overhauser field does not exceed
markedly the spectral broadening. The formation of a dynamical nuclear
polarization as well as its subsequent decay by the dipole-dipole interaction
is directly resolved in time. Because not limited by intrinsic nonlinearities,
almost complete nuclear polarization is achieved, even at elevated
temperatures. The data suggest a nonequilibrium mode of nuclear polarization,
distinctly different from the spin temperature concept exploited on bulk
semiconductorsComment: 5 pages, 4 figure
Nominally forbidden transitions in the interband optical spectrum of quantum dots
We calculate the excitonic optical absorption spectra of (In,Ga)As/GaAs
self-assembled quantum dots by adopting an atomistic pseudopotential approach
to the single-particle problem followed by a configuration-interaction approach
to the many-body problem. We find three types of allowed transitions that would
be naively expected to be forbidden. (i) Transitions that are parity forbidden
in simple effective mass models with infinite confining wells (e.g. 1S-2S,
1P-2P) but are possible by finite band-offsets and orbital-mixing effects; (ii)
light-hole--to--conduction transitions, enabled by the confinement of
light-hole states; and (iii) transitions that show and enhanced intensity due
to electron-hole configuration mixing with allowed transitions. We compare
these predictions with results of 8-band k.p calculations as well as recent
spectroscopic data. Transitions in (i) and (ii) explain recently observed
satellites of the allowed P-P transitions.Comment: Version published in Phys. Rev.
Modulation of a surface plasmon-polariton resonance by sub-terahertz diffracted coherent phonons
Coherent sub-THz phonons incident on a gold grating that is deposited on a
dielectric substrate undergo diffraction and thereby induce an alteration of
the surface plasmon-polariton resonance. This results in efficient
high-frequency modulation (up to 110 GHz) of the structure's reflectivity for
visible light in the vicinity of the plasmon-polariton resonance. High
modulation efficiency is achieved by designing a periodic nanostructure which
provides both plasmon-polariton and phonon resonances. Our theoretical analysis
shows that the dynamical alteration of the plasmon-polariton resonance is
governed by modulation of the slit widths within the grating at the frequencies
of higher-order phonon resonances.Comment: 5 pages, 4 figure
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