48 research outputs found
Uncoupled excitons in semiconductor microcavities detected in resonant Raman scattering
We present an outgoing resonant Raman-scattering study of a GaAs/AlGaAs based microcavity embedded in a p-i-n junction. The p-i-n junction allows the vertical electric field to be varied, permitting control of exciton-photon detuning and quenching of photoluminescence which otherwise obscures the inelastic light scattering signals. Peaks corresponding to the upper and lower polariton branches are observed in the resonant Raman cross sections, along with a third peak at the energy of uncoupled excitons. This third peak, attributed to disorder activated Raman scattering, provides clear evidence for the existence of uncoupled exciton reservoir states in microcavities in the strong-coupling regime
Quantum-fluid dynamics of microcavity polaritons
Semiconductor microcavities offer a unique system to investigate the physics
of weakly interacting bosons. Their elementary excitations, polaritons--a
mixture of excitons and photons--behave, in the low density limit, as bosons
that can undergo a phase transition to a regime characterised by long range
coherence. Condensates of polaritons have been advocated as candidates for
superfluidity; and the formation of vortices as well as elementary excitations
with a linear dispersion are actively sought after. In this work, we have
created and set in motion a macroscopically degenerate state of polaritons and
let it collide with a variety of defects present in the sample. Our experiments
show striking manifestations of a coherent light-matter packet that displays
features of a superfluid, although one of a highly unusual character as it
involves an out-of-equilibrium dissipative system where it travels at
ultra-fast velocity of the order of 1% the speed of light. Our main results are
the observation of i) a linear polariton dispersion accompanied with
diffusion-less motion, ii) flow without resistance when crossing an obstacle,
iii) suppression of Rayleigh scattering and iv) splitting into two fluids when
the size of the obstacle is comparable with the size of the wavepacket. This
work opens the way to the investigation of new phenomenology of
out-of-equilibrium condensates.Comment: 22 pages, 5 figure
Exploring the relation between childhood trauma, temperamental traits and mindfulness in borderline personality disorder
Background: Deficits in mindfulness-related capacities have been described in borderline personality disorder (BPD). However, little research has been conducted to explore which factors could explain these deficits. This study assesses the relationship between temperamental traits and childhood maltreatment with mindfulness in BPD. Methods: A total of 100 individuals diagnosed with BPD participated in the study. Childhood maltreatment was assessed using the Childhood Trauma Questionnaire (CTQ-SF), temperamental traits were assessed using the Zuckerman-Khulman Personality Questionnaire (ZKPQ), and mindfulness capabilities were evaluated with the Five Facet Mindfulness Questionnaire (FFMQ). Results: Hierarchical regression analyses were performed including only those CTQ-SF and ZKPQ subscales that showed simultaneous significant correlations with mindfulness facets. Results indicated that neuroticism and sexual abuse were predictors of acting with awareness; and neuroticism, impulsiveness and sexual abuse were significant predictors of non-judging. Temperamental traits did not have a moderator effect on the relationship between childhood sexual abuse and mindfulness facets. Conclusions: These results provide preliminary evidence for the effects of temperamental traits and childhood trauma on mindfulness capabilities in BPD individuals. Further studies are needed to better clarify the impact of childhood traumatic experiences on mindfulness capabilities and to determine the causal relations between these variables
The Cerenkov effect revisited: from swimming ducks to zero modes in gravitational analogs
We present an interdisciplinary review of the generalized Cerenkov emission
of radiation from uniformly moving sources in the different contexts of
classical electromagnetism, superfluid hydrodynamics, and classical
hydrodynamics. The details of each specific physical systems enter our theory
via the dispersion law of the excitations. A geometrical recipe to obtain the
emission patterns in both real and wavevector space from the geometrical shape
of the dispersion law is discussed and applied to a number of cases of current
experimental interest. Some consequences of these emission processes onto the
stability of condensed-matter analogs of gravitational systems are finally
illustrated.Comment: Lecture Notes at the IX SIGRAV School on "Analogue Gravity" in Como,
Italy from May 16th-21th, 201