Quantum simulation for peak broadening in atom lithography

A grating structure with period of half of the laser wavelength generated by focusing Cr atoms with nearly resonant laser standing wave atom lens was simulated using a quantum-mechanical model.     

Coulomb broadening of the peak of electromagnetically induced transparency in plasma

We have measured the shape of the Autler-Townes doublet and the peak of electromagnetically induced transparency (EIT) under plasma conditions. We compare the experimental results with the calculated spectrum of the probe field of a three-level ArII Λ-scheme by taking into account Coulomb collisions. We show that the Coulomb broadening of the EIT peak is small (less than 40%), while the saturation resonance is broadened under the experimental conditions by a factor of 3. In contrast to the saturation resonance attributable to the Bennett dip in the velocity distribution of the population, the EIT peak is a coherent effect and is broadened mainly through Coulomb dephasing.     

Charge density determination in icosahedral AlPdMn quasicrystal using quantitative convergent beam electron diffraction

Charge density distribution in icosahedral AlPdMn quasicrystal has been studied on a single-crystal specimen by using quantitative convergent beam electron diffraction (QCBED) technique. The QCBED systematic row method was used in the refinement of structure factors. To refine the low-order structure factors, the wave-mechanical formulation of electron diffraction dynamical theory was used in the calculation of electron diffraction intensities for the quasicrystal in fitting the experimental intensity line scan profiles. The shapes of atomic surfaces (occupation domains) were described with symmetry-adapted series of surface harmonics. An iterative procedure was used in determination of structure factors of the quasicrystal. The structure factors of nine strongest symmetry inequivalent reflections according to X-ray diffraction experiment were refined with QCBED technique. The average of refinement results for a given reflection performed on several CBED patterns, which were slightly different in orientation and sample thickness, and on different line scans, was taken as the value of structure factor for the reflection. The obtained structure factors for electrons were transformed into X-ray structure factors with Mott formula. The bonding charge density map for the quasicrystal was constructed with the obtained nine structure factors. Assuming that the atoms are spheres, the gain or loss of electrons for different atoms were calculated. It shows that identical atoms can have different valences at different kinds of positions. The bonding charge is localized along certain directions.     

Intersubband absorption peak broadening due to unscreened inhomogeneity of levels

The shape of the interband absorption peak in quantum wells with uneven heteroboundaries is studied theoretically. Although the large-scale variations of the ground level in strongly doped structures are screened, the energy of intersubband transitions remains inhomogeneous in the 2D plane due to unscreened changes of the energy of an excited level. The equations for intersubband polarization are derived taking into account the Coulomb contributions proportional to e ² and leading to a depolarization shift and the exchange renormalization of the spectrum. The shape of the intersubband absorption peak is analyzed both in the local approximation and taking into account the nonlocality of the response in the 2D plane. In the case of single-layer irregularities of heteroboundaries, this mechanism makes the main contribution to the intersubband absorption peak broadening for the far and intermediate IR range.     

Shrinking of the forward diffraction peak and multiparticle production

It is shown, that independently of any specific model for multiparticle production, the shringking with energy of the forward diffraction peak can be derived assuming local compensation (in rapidity space) of the transverse components of momenta of secondaries. A formalism suitable for this demonstration is developed and a lower bound for the “pomeron slope” is derived. This bound, which involves observable parameters only, is valid under fairly general conditions. Finally, simple experiments which can test the validity of the ideas presented in this paper are suggested.     

Resonant vibrations, peak broadening, and noise in single molecule contacts: the nature of the first conductance peak

We carry out experiments on single-molecule junctions at low temperatures, using the mechanically controlled break junction technique. Analyzing the results obtained with various molecules, the nature of the first peak in the differential conductance spectra is elucidated. We observe an electronic transition with a vibronic fine structure, if the first peak occurs at small voltages. This regime can accurately be described by the resonant tunneling model. At higher voltages, additional smearing is observed and no fine structure can be resolved. A detailed analysis of the noise signal indicates that the onset of current is associated with strong fluctuations as a precursor of current flow. The data indicate that a complex fluctuation-driven transport mechanism takes over in this regime.     

Checkerboard patterns and magnetic resonance peak in cuprate superconductors

We investigate a kind of spin-Peierls transition (SP) in high T_c superconductivity. It is found the antiferromagnetic exchange integral of SP corresponds to the magnetic resonance peak. The kind of spin-Peierls transition applied to cuprate superconductors is that without dimerization of lattice ions and with dimerization of localized hole h_Cu attached to the ion. Absence of the magnetic resonance peak in La-Sr-Cu-O results from the dimerized state of localized hole, h_Cu below T_c into tetramerized phase above T_c in SP transition without dimerization of copper-ion. The checkerboard patterns with four unit cell period originate from the SP of electronic part without ion-dimerization and from charge occupation probability of oxygen-atom around Cu.     

Desorption or disordering from diffraction peak intensity decay?

When an ordered overlayer is heated at a high enough temperature, there is loss of order that can be monitored through the decay of the peak intensity of diffraction spots. This is caused by either particle loss to the gas phase or the onset of diffusion that disorders the overlayer. With the use of model simulations on a c(2 × 2) ordered overlayer, we show how the peak intensity decay can differentiate between the two cases. We further examine the growth laws describing the growth of disorder to see if they obey similar laws as the reverse ordering processes. When no interfaces separating degenerate phases are present, disordering and ordering processes do not obey the same growth laws.     

LCD pixel shape and far-field diffraction patterns

The shape and diffraction pattern of a liquid crystal display (LCD) pixel used in a point-diffraction interferometer is qualitatively evaluated using the experimental diffraction patterns of computer-generated apertures. The diffraction patterns for apertures with contours between a circle and a square were numerically plotted from analytical expressions of these topological forms. The observed patterns are qualitatively in accordance with previous calculations of such apertures using scalar diffraction theory in the far field.     

Quantum-mathematical model of edge and peak point in Fresnel diffraction through a slit

The intensity distribution in Fresnel diffraction through a slit includes numerous small fluctuations referred to as ripples. These ripples make the modelling of the intensity distribution complicated. In this study, we examine the characteristics of the Fresnel diffraction intensity distribution to deduce the rule for the peak position and then propose two types of quantum-mathematical models to obtain the distance between the edge and the peak point. The analysis and simulation indicate that the error in the models is below 0.50 μm. The models can also be used to detect the edges of a diffraction object, and we conduct several experiments to measure the slit width. The experimental results reveal that the repetition accuracy of the method can reach 0.23 μm.     

Direct observation of double diffraction patterns

The double diffraction light intensity of two identical gratings placed parallel in the Fresnel region is sensitive to the lateral displacement ΔX, and is also affected by the air gap R between the gratings. In this note, the dependence of the double diffraction light intensity on ΔX and R for each order beam has been obtained directly by observing the intensity pattern on a screen.     

Possibility of irradiation in quasicrystal–quasicrystal tunneling junctions

We predict the external radiation with a frequency half the frequency of alternating Josephson effect to appear when a constant voltage is applied to a quasicrystal–quasicrystal tunneling junction. Thus the phenomenon typical for superconductor–superconductor junctions can be realized for a non-superconducting object. The physical background for this possibility is the “critical” behavior of the wave functions in quasicrystals and electron scattering on a quasiperiodic potential. The effect opens an avenue for new applications of quasicrystals.     

Asymmetric peak broadening in photoemission of surface states as a consequence of lateral electron confinement

In addition to the inverse lifetime, the photoemission peak width of a surface state depends on the quality of the surface. For a stepped surface, in particular, there is an energy shift of the surface state owing to the confinement of electrons. A random distribution of steps causes an asymmetric peak broadening, which is examined as a function of the shift parameter, the inverse lifetime and the mean terrace width. The model is discussed for the Cu(111) sp-surface state for which an influence of steps on the peak shape is obtained particularly for mean terrace widths less than 100 Å.     

Scaling of the diffraction peak in collisions of particles of arbitrary spins

We propose sufficient conditions which, together with some positivity properties of scattering amplitudes valid for arbitrary spins, allow one to show the existence of a scaling limit for the differential cross section for an elastic reaction in the nearly forward direction. These conditions appear to be very natural and in agreement with experiment.     

The shrinkage of the diffraction peak of the bare pomeron in QCD

The new parameterQ ₀ is introduced in our integration over transverse momentaq _t in perturbative QCD to avoid infrared divergencies. Consideringq _t >Q ₀, the distribution of wee partons in impact parameter (b _t ) and the mean radius of interaction are calculated in the framework of the leading logarithmic approximation (LLA) of perturbative QCD. It is shown that the slope of the elastic amplitude increases as \(B \propto {{\sqrt {\alpha _s In s} } \mathord{\left/ {\vphantom {{\sqrt {\alpha _s In s} } {Q_0^2 }}} \right. \kern-0em} {Q_0^2 }}\) .