40 research outputs found
Dressed atom versus exciton polariton: From Rabi oscillations to the Fermi Golden rule
We rederive the dressed atom and the exciton polariton within the {\it same}
framework to make clear that their difference only comes from the number of
electrons available for photoexcitations. Using it, we analytically show how
the time dependence of the photon number transforms from an oscillating
behavior (at the stimulated or vacuum Rabi frequency) to an exponential decay
(identical for atom and semiconductor) when the excited state lifetime
decreases. Although the matter ground state is in both cases coupled by
monochromatic photons {\it not to a continuum but to a discrete state}, this
decay yet follows a kind of Fermi Golden rule. The energy conservation it
contains, is however conceptually different
Key role of the moire potential for the quasi-condensation of interlayer excitons in van der Waals heterostructures
Interlayer excitons confined in bilayer heterostructures of transition metal
dichalcogenides (TMDs) offer a promising route to implement two-dimensional
dipolar superfluids. Here, we study the experimental conditions necessary for
the realisation of such collective state. Particularly, we show that the moire
potential inherent to TMD bilayers yields an exponential increase of the
excitons effective mass. To allow for exciton superfluidity at sizeable
temperatures it is then necessary to intercalate a high- dielectric
between the monolayers confining electrons and holes. Thus the moire lattice
depth is sufficiently weak for a superfluid phase to theoretically emerge below
a critical temperature of around 10 K. Importantly, for realistic experimental
parameters interlayer excitons quasi-condense in a state with finite momentum,
so that the superfluid is optically inactive and flows spontaneously.Comment: 6 pages, 4 figure
Spectroscopic Signatures for the Dark Bose-Einstein Condensation of Spatially Indirect Excitons
We study semiconductor excitons confined in an electrostatic trap of a GaAs
bilayer heterostructure. We evidence that optically bright excitonic states are
strongly depleted while cooling to sub-Kelvin temperatures. In return, the
other accessible and optically dark states become macroscopically occupied so
that the overall exciton population in the trap is conserved. These combined
behaviours constitute the spectroscopic signature for the mostly dark
Bose-Einstein condensation of excitons, which in our experiments is restricted
to a dilute regime within a narrow range of densities, below a critical
temperature of about 1K.Comment: 7 pages and 5 figure
Thermal excitation of Trivelpiece-Gould modes in a pure electron plasma
Thermally excited plasma modes are observed in trapped, near-thermal-equilibrium pure electron plasmas over a temperature range of 0.05<T<5 eV. The measured thermal emission spectra together with a separate measurement of the wave absorption coefficient uniquely determines the temperature. Alternately, kinetic theory including the antenna geometry and the measured mode damping (i.e. spectral width) gives the plasma impedance, obviating the reflection measurement. This non-destructive temperature diagnostic agrees well with standard diagnostics, and may be useful for expensive species such as anti-matter
Quasi-condensation of bilayer excitons in a periodic potential
We study two-dimensional excitons confined in a lattice potential, for high
fillings of the lattice sites. We show that a quasi-condensate is possibly
formed for small values of the lattice depth, but for larger ones the critical
phase-space density for quasi-condensation rapidly exceeds our experimental
reach, due to the increase of the excitons effective mass. On the other hand,
in the regime of a deep lattice potential where excitons are strongly localised
at the lattice sites, we show that an array of phase-independent
quasi-condensates, different from a Mott insulating phase, is realised.Comment: 5 pages 4 figure