7,099 research outputs found
Multifractal properties of critical eigenstates in two-dimensional systems with symplectic symmetry
The multifractal properties of electronic eigenstates at the metal-insulator
transition of a two-dimensional disordered tight-binding model with spin-orbit
interaction are investigated numerically. The correlation dimensions of the
spectral measure and of the fractal eigenstate are
calculated and shown to be related by . The exponent
describing the energy correlations of the critical
eigenstates is found to satisfy the relation .Comment: 6 pages RevTeX; 3 uuencoded, gzipped ps-figures to appear in J. Phys.
Condensed Matte
Process Development Challenges Associated with Gallium Nitride Materials
While attempting to fabricate low resistance Ohmic contacts to n-GaN and n-AlGaN, processing setbacks necessitated the development of new procedures within the Semiconductor and Microsystems Fabrication Lab (SMFL) at RIT. Photoresist coating recipes usable on GaN pieces were developed for OiR-620 and LOR-5A photoresists, and GaN was etched for the first time on the LAM4600 reactive ion etcher (RIE). The etch was successful, etched GaN at a rate of 187.2 Å/min, and exhibited selectivity between GaN and hard-baked photoresist comparable to an inductively coupled plasma (ICP) etch of the same chemical makeup. An Ohmic Ti to n-GaN contact was fabricated, but was not optimized for low resistance due to time constraints. These processing solutions will enable future GaN-based projects in the SMFL
Exactly solvable model with two conductor-insulator transitions driven by impurities
We present an exact analysis of two conductor-insulator transitions in the
random graph model. The average connectivity is related to the concentration of
impurities. The adjacency matrix of a large random graph is used as a hopping
Hamiltonian. Its spectrum has a delta peak at zero energy. Our analysis is
based on an explicit expression for the height of this peak, and a detailed
description of the localized eigenvectors and of their contribution to the
peak. Starting from the low connectivity (high impurity density) regime, one
encounters an insulator-conductor transition for average connectivity
1.421529... and a conductor-insulator transition for average connectivity
3.154985.... We explain the spectral singularity at average connectivity
e=2.718281... and relate it to another enumerative problem in random graph
theory, the minimal vertex cover problem.Comment: 4 pages revtex, 2 fig.eps [v2: new title, changed intro, reorganized
text
Scaling of Level Statistics at the Disorder-Induced Metal-Insulator Transition
The distribution of energy level separations for lattices of sizes up to
282828 sites is numerically calculated for the Anderson model.
The results show one-parameter scaling. The size-independent universality of
the critical level spacing distribution allows to detect with high precision
the critical disorder . The scaling properties yield the critical
exponent, , and the disorder dependence of the correlation
length.Comment: 11 pages (RevTex), 3 figures included (tar-compressed and uuencoded
using UUFILES), to appear in Phys.Rev. B 51 (Rapid Commun.
Evaluation of children's centres in England (ECCE) : strand 1: first survey of children's centre leaders in the most deprived areas
This report is the first output from the Evaluation of Children's Centres in England (ECCE), a six year study commissioned by the Department for Education and undertaken by NatCen Social Research, the University of Oxford and Frontier Economics. The aim of ECCE is to provide an in-depth understanding of children's centre services, including their effectiveness in relation to different management and delivery approaches and the cost of delivering different types of services. The aim of Strand 1 is to profile children’s centres in the most disadvantaged areas, providing estimates on different aspects of provision with which to select centres for subsequent stages of the evaluation and to explore different models of provision. The findings below relate to 500 children's centres that are representative of all phase 1 and 2 centres (i.e. those in the 30percent most deprived areas).</p
Gate Stack Dielectric Degradation of Rare-Earth Oxides Grown on High Mobility Ge Substrates
We report on the dielectric degradation of Rare-Earth Oxides (REOs), when
used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2)
on high mobility Ge substrates. Metal-Oxide-Semiconductor (MOS) devices with
these stacks,show dissimilar charge trapping phenomena under varying levels of
Constant- Voltage-Stress (CVS) conditions, which also influences the measured
densities of the interface (Nit) and border (NBT) traps. In the present study
we also report on C-Vg hysteresis curves related to Nit and NBT. We also
propose a new model based on Maxwell-Wagner instabilities mechanism that
explains the dielectric degradations (current decay transient behavior) of the
gate stack devices grown on high mobility substrates under CVS bias from low to
higher fields, and which is unlike to those used for other MOS devices.
Finally, the time dependent degradation of the corresponding devices revealed
an initial current decay due to relaxation, followed by charge trapping and
generation of stress-induced leakage which eventually lead to hard breakdown
after long CVS stressing.Comment: 19pages (double space), 7 figures, original research article,
Submitted to JAP (AIP
Recommended from our members
Dynamic Analysis of Double Wishbone Front Suspension Systems for Sport Motorcycles
In this paper, two alternative front suspension systems and their influence on motorcycle dynamics are investigated. Based on an existing motorcycle mathematical model, the front end is modified to accommodate both Girder and Hossack suspension systems. Both of them have in common a double wishbone design that varies the front end geometry on certain manoeuvrings and, consequently, the machine’s behaviour. The kinematics of the two systems and their impact on the motorcycle performance is analysed and compared to the well known telescopic fork suspension system. Stability study for both systems is carried out by means of root-loci methods, in which the main oscillation modes, weave and wobble, are studied and compared to the baseline model
Delocalization and spin-wave dynamics in ferromagnetic chains with long-range correlated random exchange
We study the one-dimensional quantum Heisenberg ferromagnet with exchange
couplings exhibiting long-range correlated disorder with power spectrum
proportional to , where is the wave-vector of the modulations
on the random coupling landscape. By using renormalization group, integration
of the equations of motion and exact diagonalization, we compute the spin-wave
localization length and the mean-square displacement of the wave-packet. We
find that, associated with the emergence of extended spin-waves in the
low-energy region for , the wave-packet mean-square displacement
changes from a long-time super-diffusive behavior for to a
long-time ballistic behavior for . At the vicinity of ,
the mobility edge separating the extended and localized phases is shown to
scale with the degree of correlation as .Comment: PRB to appea
Spatio-temporal conjecture for diffusion
We present here a conjecture about the equivalence between the noise density
of states of a system governed by a generalized Langevin equation and the
fluctuation in the energy density of states in a Hamiltonian system. We present
evidence of this for a disordered Heisenberg system.Comment: 6 pages, 1 figure. Submitted to Physica
Two Interacting Electrons in a Quasiperiodic Chain
We study numerically the effect of on-site Hubbard interaction U between two
electrons in the quasiperiodic Harper's equation. In the periodic chain limit
by mapping the problem to that of one electron in two dimensions with a
diagonal line of impurities of strength U we demonstrate a band of resonance
two particle pairing states starting from E=U. In the ballistic (metallic)
regime we show explicitly interaction-assisted extended pairing states and
multifractal pairing states in the diffusive (critical) regime. We also obtain
localized pairing states in the gaps and the created subband due to U, whose
number increases when going to the localized regime, which are responsible for
reducing the velocity and the diffusion coefficient in the qualitatively
similar to the non-interacting case ballistic and diffusive dynamics. In the
localized regime we find propagation enhancement for small U and stronger
localization for larger U, as in disordered systems.Comment: 14 pages Revtex file, 8 figures (split into 19 jpg figures).
(postscript versions of the jpg figures are also available upon request)
submitted to PR
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