1,710 research outputs found
A few electrons per ion scenario for the B=0 metal-insulator transition in two dimensions
We argue on the basis of experimental numbers that the B=0 metal-insulator
transition in two dimensions, observed in Si-MOSFETs and in other
two-dimensional systems, is likely to be due to a few strongly interacting
electrons, which also interact strongly with the random positively ionized
impurities. At the insulating side the electrons are all bound in pairs to the
ions. On the metallic side free electrons exist which are scattered by ions
dressed with electron-pairs and therefore alter the bare scattering potential
of the ions. The physics at the metallic side of the transition is argued to be
controlled by the classical to quantum transport cross-over leading to the
observed non-monotonous dependence of the resistivity on temperature. This few
electrons per ion scenario appears to be an experimentally realistic and
testable scenario, which can also serve as a starting point for further
theoretical analysis of the two-dimensional metal-insulator transition.Comment: 8 pages, revised version, minor change
Interface charged impurity scattering in semiconductor MOSFETs and MODFETs: temperature dependent resistivity and 2D "metallic" behavior
We present the results on the anomalous 2D transport behavior by employing
Drude-Boltzmann transport theory and taking into account the realistic charge
impurity scattering effects. Our results show quantitative agreement with the
existing experimental data in several different systems and address the origin
of the strong and non-monotonic temperature dependent resistivity.Comment: Presented at SIMD, Dec. 1999 in Hawaii. To be published in
Superlattices and Microstructures, May 2000 issu
Functional equations from generating functions: a novel approach to deriving identities for the Bernstein basis functions
The main aim of this paper is to provide a novel approach to deriving
identities for the Bernstein polynomials using functional equations. We derive
various functional equations and differential equations using generating
functions. Applying these equations, we give new proofs for some standard
identities for the Bernstein basis functions, including formulas for sums,
alternating sums, recursion, subdivision, degree raising, differentiation and a
formula for the monomials in terms of the Bernstein basis functions. We also
derive many new identities for the Bernstein basis functions based on this
approach. Moreover, by applying the Laplace transform to the generating
functions for the Bernstein basis functions, we obtain some interesting series
representations for the Bernstein basis functions.Comment: 1
Quantum Criticality at the Metal Insulator Transition
We introduce a new method to analysis the many-body problem with disorder.
The method is an extension of the real space renormalization group based on the
operator product expansion. We consider the problem in the presence of
interaction, large elastic mean free path, and finite temperatures. As a result
scaling is stopped either by temperature or the length scale set by the
diverging many-body length scale (superconductivity). Due to disorder a
superconducting instability might take place at giving rise to a
metallic phase or . For repulsive interactions at we flow
towards the localized phase which is analized within the diffusive Finkelstein
theory. For finite temperatures with strong repulsive backward interactions and
non-spherical Fermi surfaces characterized by
one finds a fixed point in the plane .
( is the disorder coupling constant,
is the particle-hole triplet interaction, is the length scale and is
the number of channels.) For weak disorder, , one obtains a metallic
behavior with the resistance
(, , and ) in good agreement with
the experiments.Comment: 35 pages, Revte
Entropic Tension in Crowded Membranes
Unlike their model membrane counterparts, biological membranes are richly
decorated with a heterogeneous assembly of membrane proteins. These proteins
are so tightly packed that their excluded area interactions can alter the free
energy landscape controlling the conformational transitions suffered by such
proteins. For membrane channels, this effect can alter the critical membrane
tension at which they undergo a transition from a closed to an open state, and
therefore influence protein function \emph{in vivo}. Despite their obvious
importance, crowding phenomena in membranes are much less well studied than in
the cytoplasm.
Using statistical mechanics results for hard disk liquids, we show that
crowding induces an entropic tension in the membrane, which influences
transitions that alter the projected area and circumference of a membrane
protein. As a specific case study in this effect, we consider the impact of
crowding on the gating properties of bacterial mechanosensitive membrane
channels, which are thought to confer osmoprotection when these cells are
subjected to osmotic shock. We find that crowding can alter the gating energies
by more than in physiological conditions, a substantial fraction of
the total gating energies in some cases.
Given the ubiquity of membrane crowding, the nonspecific nature of excluded
volume interactions, and the fact that the function of many membrane proteins
involve significant conformational changes, this specific case study highlights
a general aspect in the function of membrane proteins.Comment: 20 pages (inclduing supporting information), 4 figures, to appear in
PLoS Comp. Bio
The US stock market leads the Federal funds rate and Treasury bond yields
Using a recently introduced method to quantify the time varying lead-lag
dependencies between pairs of economic time series (the thermal optimal path
method), we test two fundamental tenets of the theory of fixed income: (i) the
stock market variations and the yield changes should be anti-correlated; (ii)
the change in central bank rates, as a proxy of the monetary policy of the
central bank, should be a predictor of the future stock market direction. Using
both monthly and weekly data, we found very similar lead-lag dependence between
the S&P500 stock market index and the yields of bonds inside two groups: bond
yields of short-term maturities (Federal funds rate (FFR), 3M, 6M, 1Y, 2Y, and
3Y) and bond yields of long-term maturities (5Y, 7Y, 10Y, and 20Y). In all
cases, we observe the opposite of (i) and (ii). First, the stock market and
yields move in the same direction. Second, the stock market leads the yields,
including and especially the FFR. Moreover, we find that the short-term yields
in the first group lead the long-term yields in the second group before the
financial crisis that started mid-2007 and the inverse relationship holds
afterwards. These results suggest that the Federal Reserve is increasingly
mindful of the stock market behavior, seen at key to the recovery and health of
the economy. Long-term investors seem also to have been more reactive and
mindful of the signals provided by the financial stock markets than the Federal
Reserve itself after the start of the financial crisis. The lead of the S&P500
stock market index over the bond yields of all maturities is confirmed by the
traditional lagged cross-correlation analysis.Comment: 12 pages, 7 figures, 1 tabl
Parallel Magnetic Field Induced Transition in Transport in the Dilute Two-Dimensional Hole System in GaAs
A magnetic field applied parallel to the two-dimensional hole system in the
GaAs/AlGaAs heterostructure, which is metallic in the absence of an external
magnetic field, can drive the system into insulating at a finite field through
a well defined transition. The value of resistivity at the transition is found
to depend strongly on density
Classical versus Quantum Effects in the B=0 Conducting Phase in Two Dimensions
In the dilute two-dimensional electron system in silicon, we show that the
temperature below which Shubnikov-de Haas oscillations become apparent is
approximately the same as the temperature below which an exponential decrease
in resistance is seen in B=0, suggesting that the anomalous behavior in zero
field is observed only when the system is in a degenerate (quantum) state. The
temperature dependence of the resistance is found to be qualitatively similar
in B=0 and at integer Landau level filling factors.Comment: 3 pages, 3 figure
Metal-Insulator Transition of Disordered Interacting Electrons
We calculate the corrections to the conductivity and compressibility of a
disordered metal when the mean free path is smaller than the screening length.
Such a condition is shown to be realized for low densities and large disorder.
Analysis of the stability of the metallic state reveals a transition to the
insulating state in two-dimensions.Comment: 11 pages, REVTEX, 1 figure included; Final versio
Universal scaling, beta function, and metal-insulator transitions
We demonstrate a universal scaling form of longitudinal resistance in the
quantum critical region of metal-insulator transitions, based on numerical
results of three-dimensional Anderson transitions (with and without magnetic
field), two-dimensional quantum Hall plateau to insulator transition, as well
as experimental data of the recently discovered two-dimensional metal-insulator
transition. The associated reflection symmetry and a peculiar logarithmic form
of the beta function exist over a wide range in which the resistance can change
by more than one order of magnitude. Interesting implications for the
two-dimensional metal-insulator transition are discussed.Comment: 4 pages, REVTEX, 4 embedded figures; minor corrections to figures and
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