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Role of Quantum Confinement in Luminescence Efficiency of Group IV Nanostructures
Experimental results obtained previously for the photoluminescence efficiency
(PL) of Ge quantum dots (QDs) are theoretically studied. A
- plot of PL versus QD diameter () resulted in an
identical slope for each Ge QD sample only when . We
identified that above 6.2 nm: due to a changing
effective mass (EM), while below 4.6 nm: due to
electron/ hole confinement. We propose that as the QD size is initially
reduced, the EM is reduced, which increases the Bohr radius and interface
scattering until eventually pure quantum confinement effects dominate at small
Low-energy excitations of a linearly Jahn-Teller coupled orbital quintet
The low-energy spectra of the single-mode h x (G+H) linear Jahn-Teller model
is studied by means of exact diagonalization. Both eigenenergies and
photoemission spectral intensities are computed. These spectra are useful to
understand the vibronic dynamics of icosahedral clusters with partly filled
orbital quintet molecular shells, for example C60 positive ions.Comment: 14 pages revte
Comment on "Linear wave dynamics explains observations attributed to dark-solitons in a polariton quantum fluid"
In a recent preprint (arXiv:1401.1128v1) Cilibrizzi and co-workers report
experiments and simulations showing the scattering of polaritons against a
localised obstacle in a semiconductor microcavity. The authors observe in the
linear excitation regime the formation of density and phase patterns
reminiscent of those expected in the non-linear regime from the nucleation of
dark solitons. Based on this observation, they conclude that previous
theoretical and experimental reports on dark solitons in a polariton system
should be revised. Here we comment why the results from Cilibrizzi et al. take
place in a very different regime than previous investigations on dark soliton
nucleation and do not reproduce all the signatures of its rich nonlinear
phenomenology. First of all, Cilibrizzi et al. consider a particular type of
radial excitation that strongly determines the observed patterns, while in
previous reports the excitation has a plane-wave profile. Most importantly, the
nonlinear relation between phase jump, soliton width and fluid velocity, and
the existence of a critical velocity with the time-dependent formation of
vortex-antivortex pairs are absent in the linear regime. In previous reports
about dark soliton and half-dark soliton nucleation in a polariton fluid, the
distinctive dark soliton physics is supported both by theory (analytical and
numerical) and experiments (both continuous wave and pulsed excitation).Comment: 4 pages, 2 figure
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