49 research outputs found
Low temperature behavior of the thermopower in disordered systems near the Anderson transition
A numerical study of wave-function and matrix-element statistics in the Anderson model of localization
Flexibiliteit en spontaniteit. De samenhang tussen samenleving, cultuur en architectuur van Curaçao
[No summary available][No summary available
Flexibiliteit en spontaniteit. De samenhang tussen samenleving, cultuur en architectuur van Curaçao
[No summary available][No summary available
The Aharonov-Bohm effect for an exciton
We study theoretically the exciton absorption on a ring shreded by a magnetic
flux. For the case when the attraction between electron and hole is
short-ranged we get an exact solution of the problem. We demonstrate that,
despite the electrical neutrality of the exciton, both the spectral position of
the exciton peak in the absorption, and the corresponding oscillator strength
oscillate with magnetic flux with a period ---the universal flux
quantum. The origin of the effect is the finite probability for electron and
hole, created by a photon at the same point, to tunnel in the opposite
directions and meet each other on the opposite side of the ring.Comment: 13 RevTeX 3.0 pages plus 4 EPS-figures, changes include updated
references and an improved chapter on possible experimental realization
The random phase property and the Lyapunov Spectrum for disordered multi-channel systems
A random phase property establishing in the weak coupling limit a link between quasi-one-dimensional random Schrödinger operators and full random matrix theory is advocated. Briefly summarized it states that the random transfer matrices placed into a normal system of coordinates act on the isotropic frames and lead to a Markov process with a unique invariant measure which is of geometric nature. On the elliptic part of the transfer matrices, this measure is invariant under the unitaries in the hermitian symplectic group of the universality class under study. While the random phase property can up to now only be proved in special models or in a restricted sense, we provide strong numerical evidence that it holds in the Anderson model of localization. A main outcome of the random phase property is a perturbative calculation of the Lyapunov exponents which shows that the Lyapunov spectrum is equidistant and that the localization lengths for large systems in the unitary, orthogonal and symplectic ensemble differ by a factor 2 each. In an Anderson-Ando model on a tubular geometry with magnetic field and spin-orbit coupling, the normal system of coordinates is calculated and this is used to derive explicit energy dependent formulas for the Lyapunov spectrum
Rapid simulation of protein motion: merging flexibility, rigidity and normal mode analyses
Protein function frequently involves conformational changes with large
amplitude on timescales which are difficult and computationally expensive to
access using molecular dynamics. In this paper, we report on the combination of
three computationally inexpensive simulation methods-normal mode analysis using
the elastic network model, rigidity analysis using the pebble game algorithm,
and geometric simulation of protein motion-to explore conformational change
along normal mode eigenvectors. Using a combination of ELNEMO and FIRST/FRODA
software, large-amplitude motions in proteins with hundreds or thousands of
residues can be rapidly explored within minutes using desktop computing
resources. We apply the method to a representative set of six proteins covering
a range of sizes and structural characteristics and show that the method
identifies specific types of motion in each case and determines their amplitude
limits.Comment: 34 pages, 22 Figures, Phys. Biol. 9 (2012
Magneto-transport in periodic and quasiperiodic arrays of mesoscopic rings
We study theoretically the transmission properties of serially connected
mesoscopic rings threaded by a magnetic flux. Within a tight-binding formalism
we derive exact analytical results for the transmission through periodic and
quasiperiodic Fibonacci arrays of rings of two different sizes. The role played
by the number of scatterers in each arm of the ring is analyzed in some detail.
The behavior of the transmission coefficient at a particular value of the
energy of the incident electron is studied as a function of the magnetic flux
(and vice versa) for both the periodic and quasiperiodic arrays of rings having
different number of atoms in the arms. We find interesting resonance properties
at specific values of the flux, as well as a power-law decay in the
transmission coefficient as the number of rings increases, when the magnetic
field is switched off. For the quasiperiodic Fibonacci sequence we discuss
various features of the transmission characteristics as functions of energy and
flux, including one special case where, at a special value of the energy and in
the absence of any magnetic field, the transmittivity changes periodically as a
function of the system size.Comment: 9 pages with 7 .eps figures included, submitted to PR
Magnetic Field Effect for Two Electrons in a Two Dimensional Random Potential
We study the problem of two particles with Coulomb repulsion in a
two-dimensional disordered potential in the presence of a magnetic field. For
the regime, when without interaction all states are well localized, it is shown
that above a critical excitation energy electron pairs become delocalized by
interaction. The transition between the localized and delocalized regimes goes
in the same way as the metal-insulator transition at the mobility edge in the
three dimensional Anderson model with broken time reversal symmetry.Comment: revtex, 7 pages, 6 figure