3 research outputs found
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
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
Spectrophotometric determination of optical parameters of lithium niobate films
Lithium niobate films on silicon substrates have been synthesized by high-frequency magnetron sputtering of a target. The spectral dependences of the reflectance in the 300â700Â nm range at small incidence angles and the angular dependence of p- and s-polarized light for a discrete set of wavelengths from 300 to 700Â nm with wavelength increments of 50Â nm, for angles of 1 arc deg, have been obtained using spectrophotometry. The refractive indicies, the film thickness and the extinction coefficients have been determined using a numerical method for solving inverse problems. The initial approximations for the solution of inverse problems have been defined using methods based on the estimation of the interference extrema positions in the reflection spectra. The resultant refractive indicies of the film differ from those typical of LiNbO3 single crystals. These differences are attributed to the structural disorder induced by the predominant crystallite orientation and the absorption in the film