2,258 research outputs found
Electron-spin beat susceptibility of excitons in semiconductor quantum wells
Recent time-resolved differential transmission and Faraday rotation
measurements of long-lived electron spin coherence in quantum wells displayed
intriguing parametric dependencies. For their understanding we formulate a
microscopic theory of the optical response of a gas of optically incoherent
excitons whose constituent electrons retain spin coherence, under a weak
magnetic field applied in the quantum well's plane. We define a spin beat
susceptibility and evaluate it in linear order of the exciton density. Our
results explain the many-body physics underlying the basic features observed in
the experimental measurements
Solar neutrino interactions: Using charged currents at SNO to tell neutral currents at Super-Kamiokande
In the presence of flavor oscillations, muon and tau neutrinos can contribute
to the Super-Kamiokande (SK) solar neutrino signal through the neutral current
process \nu_{\mu,\tau} e^{-}\to \nu_{\mu,\tau} e^{-}. We show how to separate
the \nu_e and \nu_{\mu,\tau} event rates in SK in a model independent way, by
using the rate of the charged current process \nu_e d \to p p e^{-} from the
Sudbury Neutrino Observatory (SNO) experiment, with an appropriate choice of
the SK and SNO energy thresholds. Under the additional hypothesis of no
oscillations into sterile states, we also show how to determine the absolute
^{8}B neutrino flux from the same data set, independently of the \nu_e survival
probability.Comment: 14 pages (RevTeX), incl. 3 figures (epsf), submitted to Phys. ReV.
Directional optical switching and transistor functionality using optical parametric oscillation in a spinor polariton fluid
Over the past decade, spontaneously emerging patterns in the density of
polaritons in semiconductor microcavities were found to be a promising
candidate for all-optical switching. But recent approaches were mostly
restricted to scalar fields, did not benefit from the polariton's unique
spin-dependent properties, and utilized switching based on hexagon far-field
patterns with 60{\deg} beam switching (i.e. in the far field the beam
propagation direction is switched by 60{\deg}). Since hexagon far-field
patterns are challenging, we present here an approach for a linearly polarized
spinor field, that allows for a transistor-like (e.g., crucial for
cascadability) orthogonal beam switching, i.e. in the far field the beam is
switched by 90{\deg}. We show that switching specifications such as
amplification and speed can be adjusted using only optical means
Non-Hermitian dispersion sign reversal of radiative resonances in two dimensions
In a recent publication [Wurdack et al., Nat. Comm. 14:1026 (2023)], it was
shown that in microcavities containing atomically thin semiconductors
non-Hermitian quantum mechanics can lead to negative exciton polariton masses.
We show that mass-sign reversal can occur generally in radiative resonances in
two dimensions (without cavity) and derive conditions for it (critical
dephasing threshold etc.). In monolayer transition-metal dichalcogenides, this
phenomenon is not invalidated by the strong electron-hole exchange interaction,
which is known to make the exciton massless
Gapless fluctuations and exceptional points in semiconductor lasers
We analyze the spectrum of spatially uniform, single-particle fluctuation
modes in the linear electromagnetic response of a semiconductor laser. We show
that if the decay rate of the interband polarization, , and the
relaxation rate of the occupation distribution, , are different, a
gapless regime exists in which the order parameter (linear
in the coherent photon field amplitude and the interband polarization) is
finite but there is no gap in the real part of the single-particle fluctuation
spectrum. The laser being a pumped-dissipative system, this regime may be
considered a non-equilibrium analog of gapless superconductivity. We analyze
the fluctuation spectrum in both the photon laser limit, where the interactions
among the charged particles are ignored, and the more general model with
interacting particles. In the photon laser model, the order parameter is
reduced to a momentum-independent quantity, which we denote by . We
find that, immediately above the lasing threshold, the real part of the
fluctuation spectrum remains gapless when and becomes gapped when exceeds the upper
bound of this range. Viewed as a complex function of and the
electron-hole energy, the eigenvalue set displays some interesting exceptional
point (EP) structure around the gapless-gapped transition. The transition point
is a third-order EP, where three eigenvalues (and eigenvectors) coincide.
Switching on the particle interactions in the full model modifies the spectrum
of the photon laser model and, in particular, leads to a more elaborate EP
structure. However, the overall spectral behavior of the continuous
(non-collective) modes of the full model can be understood on the basis of the
relevant results of the photon laser model
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