88 research outputs found
Impact Excitation by Hot Carriers in Carbon Nanotubes
We investigate theoretically the efficiency of intra-molecular hot carrier
induced impact ionization and excitation processes in carbon nanotubes. The
electron confinement and reduced screening lead to drastically enhanced
excitation efficiencies over those in bulk materials. Strong excitonic coupling
favors neutral excitations over ionization, while the impact mechanism
populates a different set of states than that produced by photoexcitation. The
excitation rate is strongly affected by optical phonon excitation and a simple
scaling of the rate with the field strength and optical phonon temperature is
obtained.Comment: 5 pages 4 figure
Exciton-phonon effects in carbon nanotube optical absorption
We find that the optical properties of carbon nanotubes reflect remarkably
strong effects of exciton-phonon coupling. Tight-binding calculations show that
a significant fraction of the spectral weight of the absorption peak is
transferred to a distinct exciton+phonon sideband, which is peaked at around
200 meV above the main absorption peak. This sideband provides a distinctive
signature of the excitonic character of the optical transition. The
exciton-phonon coupling is reflected in a dynamical structural distortion,
which contributes a binding energy of up to 100 meV. The distortion is
surprisingly long-ranged, and is strongly dependent on chirality.Comment: 5 pages, 3 figure
Scaling of excitons in carbon nanotubes
Light emission from carbon nanotubes is expected to be dominated by excitonic
recombination. Here we calculate the properties of excitons in nanotubes
embedded in a dielectric, for a wide range of tube radii and dielectric
environments. We find that simple scaling relationships give a good description
of the binding energy, exciton size, and oscillator strength.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Let
Atomoxetine reduces hyperactive/impulsive behaviours in neurokinin-1 receptor 'knockout' mice.
Mice with functional ablation of the neurokinin-1 receptor gene (NK1R(-/-)) display behavioural abnormalities which resemble the hyperactivity, inattention and impulsivity seen in Attention Deficit Hyperactivity Disorder (ADHD). Here, we investigated whether the established ADHD treatment, atomoxetine, alleviates these abnormalities when tested in the light/dark exploration box (LDEB) and 5-Choice Serial Reaction-Time Task (5-CSRTT)
Optical trapping with "on-demand" two-photon luminescence using Cr:LiSAF laser with optically addressed saturable Bragg reflector
We demonstrate a diode-pumped Cr:LiSAF laser with controllable and reliable fast switching between its continuous-wave and mode-locked states of operation using an optically-addressed semiconductor Bragg reflector, permitting dyed microspheres to be continuously trapped and monitored using a standard microscope imaging and on-demand two-photon-excited luminescence techniques
Reactivity of Sodium Pentaphospholide Na[cyclo-P5] towards C≡E (E=C, N, P) Triple Bonds
A diglyme solution of Na[cyclo-P5] (1) reacts with alkynes and isolobal nitriles and phosphaalkynes to afford the otherwise elusive (aza)phospholide anions 2 a–c, 4 a,b, and 6. The reaction of Na[cyclo-P5] with alkynes and nitriles was studied by means of DFT methods, which suggested a concerted mechanism for the formation of 2 a and 4 b. The anions 2 a–c, 4 a,b, and 6 coordinate in an η5-fashion towards FeII to give the sandwich (aza)phosphametallocenes 3 a–c, 5 a,b and 7 in moderate to good yields. The new compounds were characterized by means of multinuclear NMR spectroscopy, single-crystal X-ray diffraction and cyclic voltammetry
Electronically highly cubic conditions for Ru in alpha-RuCl3
We studied the local Ru 4d electronic structure of alpha-RuCl3 by means of
polarization dependent x-ray absorption spectroscopy at the Ru-L2,3 edges. We
observed a vanishingly small linear dichroism indicating that electronically
the Ru 4d local symmetry is highly cubic. Using full multiplet cluster
calculations we were able to reproduce the spectra excellently and to extract
that the trigonal splitting of the t2g orbitals is -12 meV, i.e.
negligible as compared to the Ru 4d spin-orbit coupling constant. Consistent
with our magnetic circular dichroism measurements, we found that the ratio of
the orbital and spin moments is 2.0, the value expected for a Jeff = 1/2 ground
state. We have thus shown that as far as the Ru 4d local properties are
concerned, alpha-RuCl3 is an ideal candidate for the realization of Kitaev
physics
Electron-phonon effects and transport in carbon nanotubes
We calculate the electron-phonon scattering and binding in semiconducting
carbon nanotubes, within a tight binding model. The mobility is derived using a
multi-band Boltzmann treatment. At high fields, the dominant scattering is
inter-band scattering by LO phonons corresponding to the corners K of the
graphene Brillouin zone. The drift velocity saturates at approximately half the
graphene Fermi velocity. The calculated mobility as a function of temperature,
electric field, and nanotube chirality are well reproduced by a simple
interpolation formula. Polaronic binding give a band-gap renormalization of ~70
meV, an order of magnitude larger than expected. Coherence lengths can be quite
long but are strongly energy dependent.Comment: 5 pages and 4 figure
Spin re-orientation induced anisotropic magnetoresistance switching in LaCoNiO thin films
Realization of novel functionalities by tuning magnetic interactions in rare
earth perovskite oxide thin films opens up exciting technological prospects.
Strain-induced tuning of magnetic interactions in rare earth cobaltates and
nickelates is of central importance due to their versatility in electronic
transport properties. Here we reported the spin re-orientation induced
switching of anisotropic magnetoresistance (AMR) and its tunability with strain
in epitaxial LaCoNiO thin films across the
ferromagnetic transition. Moreover, with strain tuning, we could observe a
two-fold to four-fold symmetry crossover in AMR across the magnetic transition
temperature. The magnetization measurements revealed an onset of ferromagnetic
transition around 50 K, and a further reduction in temperature showed a subtle
change in the magnetization dynamics, which reduced the ferromagnetic
long-range ordering and introduced glassiness in the system. X-ray absorption
and X-ray magnetic circular dichroism spectroscopy measurements over Co and Ni
L edges revealed the Co spin state transition below the magnetic transition
temperature leading to the AMR switching and also the presence of Ni and
Co ions evidencing the charge transfer from Ni to Co ions. Our work
demonstrated the tunability of magnetic interactions mediated electronic
transport in cobaltate-nickelate thin films, which is relevant in understanding
Ni-Co interactions in oxides for their technological applications such as in
AMR sensors
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