Transient Zitterbewegung of charge carriers in graphene and carbon nanotubes

Observable effects due to trembling motion (Zitterbewegung, ZB) of charge carriers in bilayer graphene, monolayer graphene and carbon nanotubes are calculated. It is shown that, when the charge carriers are prepared in the form of gaussian wave packets, the ZB has a transient character with the decay time of femtoseconds in graphene and picoseconds in nanotubes. Analytical results for bilayer graphene allow us to investigate phenomena which accompany the trembling motion. In particular, it is shown that the transient character of ZB in graphene is due to the fact that wave subpackets related to positive and negative electron energies move in opposite directions, so their overlap diminishes with time. This behavior is analogous to that of the wave packets representing relativistic electrons in a vacuum.Comment: 7 pages, 3 figures, augmented versio

Conduction electrons localized by charged magneto-acceptors A2−^{2-} in GaAs/GaAlAs quantum wells

A variational theory is presented of A$^{1-}$ and A$^{2-}$ centers, i.e. of a negative acceptor ion localizing one and two conduction electrons, respectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic field parallel to the growth direction. A combined effect of the well and magnetic field confines conduction electrons to the proximity of the ion, resulting in discrete repulsive energies above the corresponding Landau levels. The theory is motivated by our experimental magneto-transport results which indicate that, in a heterostructure doped in the GaAs well with Be acceptors, one observes a boil-off effect in which the conduction electrons in the crossed-field configuration are pushed by the Hall electric field from the delocalized Landau states to the localized acceptor states and cease to conduct. A detailed analysis of the transport data shows that, at high magnetic fields, there are almost no conducting electrons left in the sample. It is concluded that one negative acceptor ion localizes up to four conduction electrons.Comment: 8 pages, 5 figure

A Novel Reporter Mouse Uncovers Endogenous Brn3b Expression.

Brn3b (Pou4f2) is a class-4 POU domain transcription factor known to play central roles in the development of different neuronal populations of the Central Nervous System, including retinal ganglion cells (RGCs), the neurons that connect the retina with the visual centers of the brain. Here, we have used CRISPR-based genetic engineering to generate a Brn3b-mCherry reporter mouse without altering the endogenous expression of Brn3b. In our mouse line, mCherry faithfully recapitulates normal Brn3b expression in the retina, the optic tracts, the midbrain tectum, and the trigeminal ganglia. The high sensitivity of mCherry also revealed novel expression of Brn3b in the neuroectodermal cells of the optic stalk during early stages of eye development. Importantly, the fluorescent intensity of Brn3b-mCherry in our reporter mice allows for noninvasive live imaging of RGCs using Scanning Laser Ophthalmoscopy (SLO), providing a novel tool for longitudinal monitoring of RGCs

Risk of climate-induced damage in historical textiles

Eleven wool and silk historic textiles and two modern artist's canvases were examined to determine their water vapour adsorption, moisture dimensional response and tensile behaviour. All the textiles showed a similar general pattern of moisture response. A rise in ambient relative humidity (RH) from dry conditions produced expansion of a textile until a certain critical RH level after which a contraction occurred to a greater or lesser degree depending on the yarn crimp and the weave geometry. The largest expansion recorded between the dry state and 80% RH was 1.2 and 0.9% for wool and silk textiles, respectively. The largest shrinkage of 0.8% at high RH range was experienced by a modern linen canvas. Two potential damage mechanisms related to the moisture response of the textiles—stress building as a result of shrinkage of the textile restrained in its dimensional response and the fretting fatigue when yarns move with friction one against another—were found insignificant in typical textile display environments unless the textiles are severely degraded or excessively strained in their mounting

Cyclotron motion in graphene

We investigate cyclotron motion in graphene monolayers considering both the full quantum dynamics and its semiclassical limit reached at high carrier energies. Effects of zitterbewegung due to the two dispersion branches of the spectrum dominate the irregular quantum motion at low energies and are obtained as a systematic correction to the semiclassical case. Recent experiments are shown to operate in the semiclassical regime.Comment: 6 pages, 1 figure include

Low energy inelastic electron scattering from carbon monoxide: I. Excitation of the a³ Π, a'³ Σ ⁺ and A¹ Π electronic states

Differential scattering cross sections for electron excitation of the three lowest excited electron states of carbon monoxide are obtained experimentally using low-energy electron energy-loss spectroscopy and theoretically using the R-matrix method. The incident electron energies range from near-threshold of 6.3 eV to 20 eV. Experimental scattering angles range from 20° to 120°. The normalization of the experimental cross sections is made to available experimental elastic scattering data (Gibson et al 1996 J. Phys. B: At. Mol. Opt. Phys. 29 3197). The R-matrix calculations use three distinct close-coupling models and their results are compared to available experimental and theoretical cross sections. The overall comparison leads to significantly improved description of the excitation cross sections for this target