738 research outputs found
Optically induced transparency in bosonic cascade lasers
Bosonic cascade lasers are terahertz (THz) lasers based on stimulated
radiative transitions between bosonic condensates of excitons or
exciton-polaritons confined in a trap. We study the interaction of an incoming
THz pulse resonant in frequency with the transitions between neighboring energy
levels of the cascade. We show that at certain optical pump conditions the
cascade becomes transparent to the incident pulse: it neither absorbs nor
amplifies it, in the mean field approximation. The populations of intermediate
levels of the bosonic cascade change as the THz pulse passes, nevertheless. In
comparison, a fermionic cascade laser does not reveal any of these properties.Comment: 4 pages, 5 figure
Quantization of entropy in a quasi-two-dimensional electron gas
We demonstrate that the partial entropy of a two-dimensional electron gas
(2DEG) exhibits quantized peaks at resonances between the chemical potential
and electron levels of size quantization. In the limit of no scattering, the
peaks depend only on the subband quantization number and are independent on
material parameters, shape of the confining potential, electron effective mass
and temperature. The quantization of partial entropy is a signature of a
topological phase transition in a 2DEG. In the presence of stationary disorder,
the magnitude of peaks decreases. Its deviation from the quantized values is a
direct measure of the disorder induced smearing of the electronic density of
states.Comment: 4 pages, 2 figure
Light Mediated Superconducting Transistor
Bose-condensation of mass-less quasiparticles (photons) can be easily
achieved at the room temperature in lasers. On the other hand, condensation of
bosons having a non-zero mass requires usually ultra-low temperatures.
Recently, it has been shown that polaritons, which are half-light-half-matter
quasi-particles, may form condensed states at high temperatures (up to 300K).
Polaritons composed by electron-hole pairs coupled to confined light modes in
optical cavities may form a Bardeen-Cooper-Schriefer (BCS) superfluid. We
propose a new transistor based on stimulated scattering of electron-hole pairs
into the BCS polariton mode. A pn-junction embedded inside an optical cavity
resonantly emits light into the cavity mode. If the cavity mode energy slightly
exceeds the band-gap energy, it couples with electron-hole pairs with zero
centre of mass wave-vector but non-zero wave-vector of relative motion. This
creates a super-current in the plane of the structure. In an isotropic case,
its direction is chosen by the system spontaneously. Otherwise, it is pinned to
the external in-plane bias. We calculate the phase diagram for the
electron-hole-polariton system.Comment: 11 pages, 3 figure
Exciton-photon coupling in a ZnSe based microcavity fabricated using epitaxial liftoff
We report the observation of strong exciton-photon coupling in a ZnSe based
microcavity fabricated using epitaxial liftoff. Molecular beam epitaxial grown
ZnSe/ZnCdSe quantum wells with a one wavelength optical length
at the exciton emission were transferred to a SiO/TaO mirror with a
reflectance of 96% to form finesse matched microcavities. Analysis of our angle
resolved transmission spectra reveals key features of the strong coupling
regime: anticrossing with a normal mode splitting of at ;
composite evolution of the lower and upper polaritons; and narrowing of the
lower polariton linewidth near resonance. The heavy hole exciton oscillator
strength per quantum well is also deduced to be .Comment: 3 pages, 3 figure
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