672 research outputs found
Instanton theory for bosons in disordered speckle potential
We study the tail of the spectrum for non-interacting bosons in a
blue-detuned random speckle potential. Using an instanton approach we derive
the asymptotic behavior of the density of states in d dimensions. The leading
corrections resulting from fluctuations around the saddle point solution are
obtained by means of the Gel'fand-Yaglom method generalized to functional
determinants with zero modes. We find a good agreement with the results of
numerical simulations in one dimension. The effect of weak repulsive
interactions in the Lifshitz tail is also discussed.Comment: 12 pages, 3 figures, revtex
Wave function correlations and the AC conductivity of disordered wires beyond the Mott-Berezinskii law
In one-dimensional disordered wires electronic states are localized at any
energy. Correlations of the states at close positive energies and the AC
conductivity in the limit of small frequency are described by
the Mott-Berezinskii theory. We revisit the instanton approach to the
statistics of wave functions and AC transport valid in the tails of the
spectrum (large negative energies). Applying our recent results on functional
determinants, we calculate exactly the integral over gaussian fluctuations
around the exact two-instanton saddle point. We derive correlators of wave
functions at different energies beyond the leading order in the energy
difference. This allows us to calculate corrections to the Mott-Berezinskii law
(the leading small frequency asymptotic behavior of ) which
approximate the exact result in a broad range of . We compare our
results with the ones obtained for positive energies.Comment: 7 pages, 3 figure
Ion-Beam-Induced Defects in CMOS Technology: Methods of Study
Ion implantation is a nonequilibrium doping technique, which introduces impurity atoms into a solid regardless of thermodynamic considerations. The formation of metastable alloys above the solubility limit, minimized contribution of lateral diffusion processes in device fabrication, and possibility to reach high concentrations of doping impurities can be considered as distinct advantages of ion implantation. Due to excellent controllability, uniformity, and the dose insensitive relative accuracy ion implantation has grown to be the principal doping technology used in the manufacturing of integrated circuits. Originally developed from particle accelerator technology, ion implanters operate in the energy range from tens eV to several MeV (corresponding to a few nms to several microns in depth range). Ion implantation introduces point defects in solids. Very minute concentrations of defects and impurities in semiconductors drastically alter their electrical and optical properties. This chapter presents methods of defect spectroscopy to study the defect origin and characterize the defect density of states in thin film and semiconductor interfaces. The methods considered are positron annihilation spectroscopy, electron spin resonance, and approaches for electrical characterization of semiconductor devices
Electrical properties of Bi-implanted amorphous chalcogenide films
The impact of Bi implantation on the conductivity and the thermopower of
GeTe, Ge-Sb-Te, and Ga- La-S films is investigated. The enhanced conductivity
appears to be notably sensitive to a dose of an implant. Incorporation of Bi in
amorphous chalcogenide films at doses up to 1x1015 cm-2 is seen not to change
the majority carrier type and activation energy for the conduction process.
Higher implantation doses may reverse the majority carrier type in the studied
films. Electron conductivity was observed in GeTe films implanted with Bi at a
dose of 2x1016 cm-2. These studies indicate that native coordination defects
present in amorphous chalcogenide semiconductors can be deactivated by means of
ion implantation. A substantial density of implantation-induced traps in the
studied films and their interfaces with silicon is inferred from analysis of
the space-charge limited current and capacitance-voltage characteristics taken
on Au/amorphous chalcogenide/Si structures.Comment: arXiv admin note: substantial text overlap with arXiv:1410.567
The Time-Course of Lexical and Structural Processes in Sentence Comprehension
Online sentence comprehension involves multiple types of cognitive processes: lexical processes such as lexical access, which call on the user's knowledge of the meaning of words in the language, and structural processes such as the integration of incoming words into an emerging representation. In this article, we investigate the temporal dynamics of lexical access and syntactic integration. Unlike much previous work that has relied on temporary ambiguity to investigate this question, we manipulate the frequency of the verb in unambiguous structures involving a well-studied syntactic complexity manipulation (subject- vs. object-extracted clefts). The results demonstrate that for high-frequency verbs, the difficulty of reading a more structurally complex object-extracted cleft structure relative to a less structurally complex subject-extracted cleft structure is largely experienced in the cleft region, whereas for low-frequency verbs this difficulty is largely experienced in the postcleft region. We interpret these results as evidence that some stages of structural processing follow lexical processing. Furthermore, we find evidence that structural processing may be delayed if lexical processing is costly, and that the delay is proportional to the difficulty of the lexical process. Implications of these results for contemporary accounts of sentence comprehension are discussed
Surface segregation of conformationally asymmetric polymer blends
We have generalized the Edwards' method of collective description of dense
polymer systems in terms of effective potentials to polymer blends in the
presence of a surface. With this method we have studied conformationally
asymmetric athermic polymer blends in the presence of a hard wall to the first
order in effective potentials. For polymers with the same gyration radius
but different statistical segment lengths and the excess
concentration of stiffer polymers at the surface is derived as % \delta \rho
_{A}(z=0)\sim (l_{B}^{-2}-l_{A}^{-2}){\ln (}R_{g}^{2}/l_{c}^{2}{)%}, where
is a local length below of which the incompressibility of the polymer
blend is violated. For polymer blends differing only in degrees of
polymerization the shorter polymer enriches the wall.Comment: 11 pages, 7 figures, revtex
Density of states in an optical speckle potential
We study the single particle density of states of a one-dimensional speckle
potential, which is correlated and non-Gaussian. We consider both the repulsive
and the attractive cases. The system is controlled by a single dimensionless
parameter determined by the mass of the particle, the correlation length and
the average intensity of the field. Depending on the value of this parameter,
the system exhibits different regimes, characterized by the localization
properties of the eigenfunctions. We calculate the corresponding density of
states using the statistical properties of the speckle potential. We find good
agreement with the results of numerical simulations.Comment: 11 pages, 11 figures, revtex
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