20 research outputs found
Coupled system of electrons and exciton-polaritons: Screening, dynamical effects, and superconductivity
Bose-Fermi systems such as mixtures of electrons with excitons or
exciton-polaritons are extensively discussed as candidates to host a variety of
intriguing phenomena, including polaron formation, drag effects, supersolidity,
and superconductivity. In this work, assuming the strong-coupling regime
between the semiconductor excitons and cavity photons, we develop the many-body
theory approach addressing the interplay of different types of interaction
among various species in such a mixture, wherein we take into account dynamical
density responses of both the Bose-condensed exciton-polaritons and the
two-dimensional electron gas inside an optical microcavity. As was anticipated
previously, at high enough polariton densities the lower hybrid mode of the
system's excitation spectrum acquires a roton minimum, making the system prone
to superconducting pairing in the vicinity of the roton instability. We analyze
the possibility of polariton-BEC-mediated superconductivity in the electron gas
taking into account full momentum and frequency dependence of the gap, as well
as in the Eliashberg approach where the momentum dependence is neglected, and
in the Bardeen-Cooper-Schrieffer approach that discards the frequency
dependence and dynamical effects. Considering the interaction screening in
Thomas-Fermi and in random-phase approximations, we estimate the critical
temperatures of superconductivity to be not larger than 0.1 K in the vicinity
of instability. As possible realizations of the coupled polariton-electron
system, semiconductor quantum wells and two-dimensional transition metal
dichalcogenides are considered.Comment: 19 pages, 8 figure
Tunable Bose-Einstein condensation and roton-like excitation spectra with dipolar exciton-polaritons in crossed fields
We develop the many-body theory of dipolar exciton-polaritons in an optical
microcavity in crossed transverse electric and in-plane magnetic fields. Even
for relatively weak fields, we reveal the existence of two minima in the bare
lower-polariton dispersion, which give rise to the tuneable transition between
the polariton Bose-Einstein condensate and that of excitons, produced by the
competition between these minima. We predict that such dipolar condensate
exhibits a roton-maxon character of the excitation spectrum, never before
observed for polaritons. We show that upon the transition between the two
condensation regimes, the weak correlations in the polariton gas give way to
the intermediate interparticle correlations characteristic for excitons, and
that the transition is accompanied by a sharp quenching of photoluminescence as
the lifetime is increased by several orders of magnitude. While in the
polariton regime, the luminescence peak corresponding to the condensate is
shifted to a non-zero angle. The angular dependence of the two-photon decay
time in the Hanbury Brown and Twiss experiment is calculated and used as a tool
to evidence the formation of the macroscopically-coherent state. Our proposal
opens opportunities towards manipulating the superfluid properties and
extended-range dipole-dipole correlations of exciton-polariton condensates.Comment: 16 pages, 6 figure
Topologically driven Rabi-oscillating interference dislocation
Quantum vortices are the quantized version of classical vortices. Their
center is a phase singularity or vortex core around which the flow of particles
as a whole circulates and is typical in superfluids, condensates and optical
fields. However, the exploration of the motion of the phase singularities in
coherently-coupled systems is still underway. We theoretically analyze the
propagation of an interference dislocation in the regime of strong coupling
between light and matter, with strong mass imbalance, corresponding to the case
of microcavity exciton-polaritons. To this end, we utilize combinations of
vortex and tightly focused Gaussian beams, which are introduced through
resonant pulsed pumping. We show that a dislocation originates from
self-interference fringes, due to the non-parabolic dispersion of polaritons
combined with moving Rabi-oscillating vortices. The morphology of singularities
is analyzed in the Poincar\'{e} space for the pseudospin associated to the
polariton states. The resulting beam carries orbital angular momentum with
decaying oscillations due to the loss of overlap between the normal modes of
the polariton system.Comment: 9 pages, 6 figure
Global patterns in genomic diversity underpinning the evolution of insecticide resistance in the aphid crop pest Myzus persicae
Abstract: The aphid Myzus persicae is a destructive agricultural pest that displays an exceptional ability to develop resistance to both natural and synthetic insecticides. To investigate the evolution of resistance in this species we generated a chromosome-scale genome assembly and living panel of >110 fully sequenced globally sampled clonal lines. Our analyses reveal a remarkable diversity of resistance mutations segregating in global populations of M. persicae. We show that the emergence and spread of these mechanisms is influenced by hostâplant associations, uncovering the widespread coâoption of a host-plant adaptation that also offers resistance against synthetic insecticides. We identify both the repeated evolution of independent resistance mutations at the same locus, and multiple instances of the evolution of novel resistance mechanisms against key insecticides. Our findings provide fundamental insights into the genomic responses of global insect populations to strong selective forces, and hold practical relevance for the control of pests and parasites.Peer reviewedFinal Published versio
BioDATA - Biodiversity Data for Internationalisation in Higher Education
BioDATA is an international project on developing skills in biodiversity data management and data publishing. Between 2018 and 2021, undergraduate and postgraduate students from Armenia, Belarus, Tajikistan, and Ukraine, have an opportunity to take part in the intensive courses to become certified professionals in biodiversity data management. They will gain practical skills and obtain appropriate knowledge on: international data standards (Darwin Core); data cleaning software, data publishing software such as the Integrated Publishing Toolkit (IPT), and preparation of data papers. Working with databases, creating datasets, managing data for statistical analyses and publishing research papers are essential for the everyday tasks of a modern biologist. At the same time, these skills are rarely taught in higher education. Most of the contemporary professionals in biodiversity have to gain these skills independently, through colleagues, or through supervision. In addition, all the participants familiarize themselves with one of the important international research data infrastructures such as the Global Biodiversity Information Facility (GBIF). The project is coordinated by the University of Oslo (Norway) and supported by the Global Biodiversity Information Facility (GBIF). The project is funded by the Norwegian Agency for International Cooperation and Quality Enhancement in Higher Education (DIKU)