Recent high-resolution absorption spectroscopy on excited excitons in cuprous oxide [Nature 514, 343 (2014)] has revealed significant deviations of their spectrum from that of the ideal hydrogenlike series. Here we show that the complex band dispersion of the crystal, determining the kinetic energies of electrons and holes, strongly affects the exciton binding energies. Specifically, we show that the nonparabolicity of the band dispersion is the main cause of the deviation from the hydrogen series. Experimental data collected from high-resolution absorption spectroscopy in electric fields validate the assignment of the deviation to the nonparabolicity of the band dispersion.
We study the Rydberg exciton absorption of Cu_{2}O in the presence of free carriers injected by above-band-gap illumination. Already at plasma densities ρ_{EH} below one hundredth electron-hole pair per μm^{3}, exciton lines are bleached, starting from the highest observed principal quantum number, while their energies remain constant. Simultaneously, the band gap decreases by correlation effects with the plasma. An exciton line loses oscillator strength when the band gap approaches its energy, vanishing completely at the crossing point. Adapting a plasma-physics description, we describe the observations by an effective Bohr radius that increases with rising plasma density, reflecting the Coulomb interaction screening by the plasma.
M. citrifolia is a tropical plant with a long tradition of medicinal use in Polynesia and tropical parts of eastern Asia and Australia. One of its favorite uses is the treatment of painful inflammatory conditions, such as arthritis. The analgesic activity of Noni fruit puree on mice was investigated using the hot plate test. A 10% solution of freeze concentrated Noni fruit puree in the drinking water of mice reduced the pain sensitivity comparably to the central analgesic drug tramadol. This effect was only partly reversed by the application of the morphine antagonist naloxone. An alcohol extract of noni fruit puree also caused an inhibition of MMP-9 release from human monocytes after stimulation with LPS. This effect was comparable to hydrocortisone (10(-5) m). The findings suggest that preparations of noni fruits are effective in decreasing pain and joint destruction caused by arthritis.
We demonstrate that the optical linewidth of Rydberg excitons in Cu 2 O can be completely explained by scattering with acoustical and optical phonons, whereby the dominant contributions stems from the non-polar optical 3 Gand 5 Gmodes. The consequences for the observation of polariton effects are discussed. We find that an anti-crossing of photon and exciton dispersions exists only for states with main quantum numbers n>28, so polariton effects do not play any role in the experiments reported up to now.
The basic theoretical foundation for the modelling of phonon-assisted absorption spectra in direct bandgap semiconductors, introduced by Elliott 60 years ago 1 using second order perturbation theory, results in a square root shaped dependency close to the absorption edge. A careful analysis of the experiments 2 reveals that for the yellow S excitons in Cu2O the lineshape does not follow that square root dependence. The reexamination of the theory shows that the basic assumptions of constant matrix elements and constant energy denominators is invalid for semiconductors with dominant exciton effects like Cu2O, where the phonon-assisted absorption proceeds via intermediate exciton states. The overlap between these and the final exciton states strongly determines the dependence of the absorption on the photon energy. To describe the experimental observed line shape of the indirect absorption of the yellow S exciton states we find it necessary to assume a momentum dependent deformation potential for the optical phonons.
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