103 research outputs found
Dynamics of a nanowire superlattice in an ac electric field
With a one-band envelope function theory, we investigate the dynamics of a
finite nanowire superlattice driven by an ac electric field by solving
numerically the time-dependent Schroedinger equation. We find that for an ac
electric field resonant with two energy levels located in two different
minibands, the coherent dynamics in nanowire superlattices is much more complex
as compared to the standard two-level description. Depending on the energy
levels involved in the transitions, the coherent oscillations exhibit different
patterns. A signature of barrier-well inversion phenomenon in nanowire
superlattices is also obtained.Comment: 14 pages, 4 figure
Analysis of optical properties of strained semiconductor quantum dots for electromagnetically induced transparency
Using multiband k*p theory we study the size and geometry dependence on the
slow light properties of conical semiconductor quantum dots. We find the V-type
scheme for electromagnetically induced transparency (EIT) to be most favorable,
and identify an optimal height and size for efficient EIT operation. In case of
the ladder scheme, the existence of additional dipole allowed intraband
transitions along with an almost equidistant energy level spacing adds
additional decay pathways, which significantly impairs the EIT effect. We
further study the influence of strain and band mixing comparing four different
k*p band structure models. In addition to the separation of the heavy and light
holes due to the biaxial strain component, we observe a general reduction in
the transition strengths due to energy crossings in the valence bands caused by
strain and band mixing effects. We furthermore find a non-trivial quantum dot
size dependence of the dipole moments directly related to the biaxial strain
component. Due to the separation of the heavy and light holes the optical
transition strengths between the lower conduction and upper most valence-band
states computed using one-band model and eight-band model show general
qualitative agreement, with exceptions relevant for EIT operation.Comment: 9 pages, 12 figure
Ellipticity weakens chameleon screening
The chameleon mechanism enables a long-range fifth force to be screened in dense environments when nontrivial self-interactions of the field cause its mass to increase with the local density. To date, chameleon fifth forces have mainly been studied for spherically symmetric sources; however, the nonlinear self-interactions mean that the chameleon responds to changes in the shape of the source differently to gravity. In this work we focus on ellipsoidal departures from spherical symmetry and compute the full form of the chameleon force, comparing its shape dependence to that of gravity. Enhancement of the chameleon force by up to 40% is possible when deforming a sphere to an ellipsoid of the same mass, with an ellipticity âŒ0.99
Optical properties and optimization of electromagnetically induced transparency in strained InAs/GaAs quantum dot structures
Unified treatment of coupled optical and acoustic phonons in piezoelectric cubic materials
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