100 research outputs found
Comment on "Topological stability of the half-vortices in spinor exciton-polariton condensates"
We show that recent paper by Flayac et al. [Phys. Rev. B 81, 045318 (2010)
and arXiv:0911.1650] is misleading. We demonstrate the existence of static
half-quantum vortices in exciton-polariton condensates and calculate the
warping of their polarization texture produced by TE-TM splitting of polariton
band.Comment: 4 pages, 1 figure. More material was added (in particular, on the
current flow)
Vortices in exciton-polariton condensates with polarization splitting
The presence of polarization splitting of exciton-polariton branches in
planar semiconductor microcavities has a pronounced effect on vortices in
polariton condensates. We show that the TE-TM splitting leads to the coupling
between the left and right half-vortices (vortices in the right and left
circular components of the condensate), that otherwise do not interact. We
analyze also the effect of linear polarization pinning resulted from a fixed
splitting between two perpendicular linear polarizations. In this case,
half-vortices acquire strings (solitons) attached to them. The half-vortices
with strings can be detected by observing the interference fringes of light
emitted from the cavity in two circular polarizations. The string affects the
fringes in both polarizations. Namely, the half-vortex is characterized by an
asymmetric fork-like dislocation in one circular polarization; the fringes in
the other circular polarization are continuous, but they are shifted by
crossing the string.Comment: 4 pages, 2 figs, Optics of Excitons in Confined Systems 11 (Madrid,
7-11 september 2009
Radiative coupling and weak lasing of exciton-polariton condensates
In spite of having finite life-time exciton-polaritons in microcavities are
known to condense at strong enough pumping of the reservoir. We present an
analytical theory of such Bose-condensates on a set of localized one-particle
states: condensation centers. To understand physics of these arrays one has to
supplement the Josephson coupling by the radiative coupling caused by the
interference of the light emitted by different centers. Combination of these
couplings with the one-site interaction between the bosons leads to a rich
nonlinear dynamics. In particular, a new regime of radiation appears. We call
it weak lasing: the centers have macroscopic occupations and radiate
coherently, but the coupling alone is sufficient for stabilization. The system
can have several stable states and switch between them. Moreover, the time
reversal symmetry in this regime is, as a rule, broken. A number of existing
experimental puzzles find natural interpretation in the framework of this
theory.Comment: 5 pages, 2 figure
Pseudo diamagnetism of four component exciton condensates
We analyze the spin structure of the ground state of four-component exciton
condensates in coupled quantum wells as a function of spin-dependent
interactions and applied magnetic field. The four components correspond to the
degenerate exciton states characterized by and spin projections
to the axis of the structure. We show that in a wide range of parameters, the
chemical potential of the system increases as a function of magnetic field,
which manifests a pseudo-diamagnetism of the system. The transitions to
polarized two- and one-component condensates can be of the first-order in this
case. The predicted effects are caused by energy conserving mixing of
and excitons.Comment: 4 pages, 2 figure
The Lausanne Infant Crying Stress Paradigm: Validation of an Early Postpartum Stress Paradigm with Women at Low vs. High Risk of Childbirth-Related Posttraumatic Stress Disorder.
Stress reactivity is typically investigated in laboratory settings, which is inadequate for mothers in maternity settings. This study aimed at validating the Lausanne Infant Crying Stress Paradigm (LICSP) as a new psychosocial stress paradigm eliciting psychophysiological stress reactivity in early postpartum mothers (n = 52) and to compare stress reactivity in women at low (n = 28) vs. high risk (n = 24) of childbirth-related posttraumatic stress disorder (CB-PTSD). Stress reactivity was assessed at pre-, peri-, and post-stress levels through salivary cortisol, heart rate variability (high-frequency (HF) power, low-frequency (LF) power, and LF/HF ratio), and perceived stress via a visual analog scale. Significant time effects were observed for all stress reactivity outcomes in the total sample (all p < 0.01). When adjusting for perceived life threat for the infant during childbirth, high-risk mothers reported higher perceived stress (p < 0.001, d = 0.91) and had lower salivary cortisol release (p = 0.023, d = 0.53), lower LF/HF ratio (p < 0.001, d = 0.93), and marginally higher HF power (p = 0.07, d = 0.53) than low-risk women. In conclusion, the LICSP induces subjective stress and autonomic nervous system (ANS) reactivity in maternity settings. High-risk mothers showed higher perceived stress and altered ANS and hypothalamic-pituitary-adrenal reactivity when adjusting for infant life threat. Ultimately, the LICSP could stimulate (CB-)PTSD research
Twist of generalized skyrmions and spin vortices in a polariton superfluid
We study the spin vortices and skyrmions coherently imprinted into an exciton-polariton condensate on a planar semiconductor microcavity. We demonstrate that the presence of a polarization anisotropy can induce a complex dynamics of these structured topologies, leading to the twist of their circuitation on the Poincare sphere of polarizations. The theoretical description of the results carries the concept of generalized quantum vortices in two-component superfluids, which are conformal with polarization loops around an arbitrary axis in the pseudospin space
Magneto-shear modes and a.c. dissipation in a two-dimensional Wigner crystal
The a.c. response of an unpinned and finite 2D Wigner crystal to electric
fields at an angular frequency has been calculated in the dissipative
limit, , where is the scattering rate. For
electrons screened by parallel electrodes, in zero magnetic field the
long-wavelength excitations are a diffusive longitudinal transmission line mode
and a diffusive shear mode. A magnetic field couples these modes together to
form two new magneto-shear modes. The dimensionless coupling parameter where and are the
speeds of transverse and longitudinal sound in the collisionless limit and
and are the tensor components of the
magnetoconductivity. For , both the coupled modes contribute
to the response of 2D electrons in a Corbino disk measurement of
magnetoconductivity. For , the electron crystal rotates rigidly in
a magnetic field. In general, both the amplitude and phase of the measured a.c.
currents are changed by the shear modulus. In principle, both the
magnetoconductivity and the shear modulus can be measured simultaneously.Comment: REVTeX, 7 pp., 4 eps figure
Vortices in polariton OPO superfluids
This chapter reviews the occurrence of quantised vortices in polariton
fluids, primarily when polaritons are driven in the optical parametric
oscillator (OPO) regime. We first review the OPO physics, together with both
its analytical and numerical modelling, the latter being necessary for the
description of finite size systems. Pattern formation is typical in systems
driven away from equilibrium. Similarly, we find that uniform OPO solutions can
be unstable to the spontaneous formation of quantised vortices. However,
metastable vortices can only be injected externally into an otherwise stable
symmetric state, and their persistence is due to the OPO superfluid properties.
We discuss how the currents charactering an OPO play a crucial role in the
occurrence and dynamics of both metastable and spontaneous vortices.Comment: 40 pages, 16 figure
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