1,950 research outputs found
AEM of extraterrestrial materials
Modifications to and maintenance of the JEOL 100 CX electron microscope are discussed. Research activity involving extraterrestrial matter, cosmic dust, stratosphere dust, and meteorites is summarized
Dynamics of a nano-scale rotor driven by single-electron tunneling
We investigate theoretically the dynamics and the charge transport properties
of a rod-shaped nano-scale rotor, which is driven by a similar mechanism as the
nanomechanical single-electron transistor (NEMSET). We show that a static
electric potential gradient can lead to self-excitation of oscillatory or
continuous rotational motion. The relevant parameters of the device are
identified and the dependence of the dynamics on these parameters is studied.
We further discuss how the dynamics is related to the measured current through
the device. Notably, in the oscillatory regime, we find a negative differential
conductance. The current-voltage characteristics can be used to infer details
of the surrounding environment which is responsible for damping
Phase diagram of localization in a magnetic field
The phase diagram of localization is numerically calculated for a
three-dimensional disordered system in the presence of a magnetic field using
the Peierls substitution. The mobility edge trajectory shifts in the
energy-disorder space when increasing the field. In the band center, localized
states near the phase boundary become delocalized. The obtained field
dependence of the critical disorder is in agreement with a power law behavior
expected from scaling theory. Close to the tail of the band the magnetic field
causes localization of extended states.Comment: 4 pages, RevTeX, 3 PS-figures (4 extra references are included, minor
additions), to appear in Phys. Rev. B as a Brief Repor
The three-dimensional Anderson model of localization with binary random potential
We study the three-dimensional two-band Anderson model of localization and
compare our results to experimental results for amorphous metallic alloys
(AMA). Using the transfer-matrix method, we identify and characterize the
metal-insulator transitions as functions of Fermi level position, band
broadening due to disorder and concentration of alloy composition. The
appropriate phase diagrams of regions of extended and localized electronic
states are studied and qualitative agreement with AMA such as Ti-Ni and Ti-Cu
metallic glasses is found. We estimate the critical exponents nu_W, nu_E and
nu_x when either disorder W, energy E or concentration x is varied,
respectively. All our results are compatible with the universal value nu ~ 1.6
obtained in the single-band Anderson model.Comment: 9 RevTeX4 pages with 11 .eps figures included, submitted to PR
Weak Field Phase Diagram for an Integer Quantum Hall Liquid
We study the localization properties in the transition from a two-dimensional
electron gas at zero magnetic field into an integer quantum Hall (QH) liquid.
By carrying out a direct calculation of the localization length for a finite
size sample using a transfer matrix technique, we systematically investigate
the field and disorder dependences of the metal-insulator transition in the
weak field QH regime. We obtain a different phase diagram from the one
conjectured in previous theoretical studies. In particular, we find that: (1)
the extended state energy for each Landau level (LL) is {\it always}
linear in magnetic field; (2) for a given Landau level and disorder
configuration there exists a critical magnetic field below which the
extended state disappears; (3) the lower LLs are more robust to the
metal-insulator transition with smaller . We attribute the above results
to strong LL coupling effect. Experimental implications of our work are
discussed.Comment: 4 pages, ReVTeX 3.0, 4 figures (available upon request
Renormalization group approach to energy level statistics at the integer quantum Hall transition
We extend the real-space renormalization group (RG) approach to the study of
the energy level statistics at the integer quantum Hall (QH) transition.
Previously it was demonstrated that the RG approach reproduces the critical
distribution of the {\em power} transmission coefficients, i.e., two-terminal
conductances, , with very high accuracy. The RG flow of
at energies away from the transition yielded the value of the critical
exponent, , that agreed with most accurate large-size lattice simulations.
To obtain the information about the level statistics from the RG approach, we
analyze the evolution of the distribution of {\em phases} of the {\em
amplitude} transmission coefficient upon a step of the RG transformation. From
the fixed point of this transformation we extract the critical level spacing
distribution (LSD). This distribution is close, but distinctively different
from the earlier large-scale simulations. We find that away from the transition
the LSD crosses over towards the Poisson distribution. Studying the change of
the LSD around the QH transition, we check that it indeed obeys scaling
behavior. This enables us to use the alternative approach to extracting the
critical exponent, based on the LSD, and to find very close
to the value established in the literature. This provides additional evidence
for the surprising fact that a small RG unit, containing only five nodes,
accurately captures most of the correlations responsible for the
localization-delocalization transition.Comment: 10 pages, 11 figure
Delocalization of electrons in a Random Magnetic Field
Delocalization problem for a two-dimensional non-interacting electron system
is studied under a random magnetic field. With the presence of a random
magnetic field, the Hall conductance carried by each eigenstate can become
nonzero and quantized in units of . Extended states are characterized by
nonzero Hall conductance, and by studying finite-size scaling of the density of
extended states, an insulator-metal phase transition is revealed. The metallic
phase is found at the center of energy band which is separated from the
localized states at the band tails by critical energies . Both
localization exponent and the critical energy are shown to be dependent
on the strength of random magnetic field.Comment: 9 pages, Revtex, 3 figures available upon reques
Density of states in the non-hermitian Lloyd model
We reconsider the recently proposed connection between density of states in
the so-called ``non-hermitian quantum mechanics'' and the localization length
for a particle moving in random potential. We argue that it is indeed possible
to find the localization length from the density of states of a non-hermitian
random ``Hamiltonian''. However, finding the density of states of a
non-hermitian random ``Hamiltonian'' remains an open problem, contrary to
previous findings in the literature.Comment: 6 pages, RevTex, two-column
The relationships between internal and external threat and right-wing attitudes: A three-wave longitudinal study
The interplay between threat and right-wing attitudes has received much research attention, but its longitudinal relationship has hardly been investigated. In this study, we investigated the longitudinal relationships between internal and external threat and right-wing attitudes using a cross-lagged design at three different time points in a large nationally representative sample (N = 800). We found evidence for bidirectional relationships. Higher levels of external threat were related to higher levels of Right-Wing Authoritarianism and to both the egalitarianism and dominance dimensions of Social Dominance Orientation at a later point in time. Conversely, higher levels of RWA were also related to increased perception of external threat later in time. Internal threat did not yield significant direct or indirect longitudinal relationships with right-wing attitudes. Theoretical and practical implications of these longitudinal effects are discussed
Phase Diagram of Integer Quantum Hall Effect
The phase diagram of integer quantum Hall effect is numerically determined in
the tight-binding model, which can account for overall features of recently
obtained experimental phase diagram. In particular, the quantum Hall plateaus
are terminated by two distinct insulating phases, characterized by the Hall
resistance with classic and quantized values, respectively, which is also in
good agreement with experiments.Comment: 4 pages, RevTex, 4 PostScript figures; one new figure is added; minor
modifications in the tex
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