784 research outputs found
Comment on ``Periodic wave functions and number of extended states in random dimer systems'
There are no periodic wave-functions in the RDM but close to the critical
energies there exist periodic envelopes. These envelopes are given by the
non-disordered properties of the system.Comment: RevTex file, 1 page, Comment X. Huang, X. Wu and C. Gong, Phys. Rev.
B 55, 11018 (1997
Localization Properties of the Periodic Random Anderson Model
We consider diagonal disordered one-dimensional Anderson models with an
underlying periodicity. We assume the simplest periodicity, i.e., we have
essentially two lattices, one that is composed of the random potentials and the
other of non-random potentials. Due to the periodicity special resonance
energies appear, which are related to the lattice constant of the non-random
lattice. Further on two different types of behaviors are observed at the
resonance energies. When a random site is surrounded by non-random sites, this
model exhibits extended states at the resonance energies, whereas otherwise all
states are localized with, however, an increase of the localization length at
these resonance energies. We study these resonance energies and evaluate the
localization length and the density of states around these energies.Comment: 4 page
Quantum Dynamics of Spins Coupled by Electrons in 1D Channel
We develop a unified theoretical description of the induced interaction and
quantum noise in a system of two spins (qubits) coupled via a
quasi-one-dimensional electron gas in the Luttinger liquid regime. Our results
allow evaluation of the degree of coherence in quantum dynamics driven by the
induced indirect exchange interaction of localized magnetic moments due to
conduction electrons, in channel geometries recently experimentally studied for
qubit control and measurement.Comment: 2 figures, in REVTE
Phase diagram of the integer quantum Hall effect in p-type Germanium
We experimentally study the phase diagram of the integer quantized Hall
effect, as a function of density and magnetic field. We used a two dimensional
hole system confined in a Ge/SiGe quantum well, where all energy levels are
resolved, because the Zeeman splitting is comparable to the cyclotron energy.
At low fields and close to the quantum Hall liquid-to-insulator transition, we
observe the floating up of the lowest energy level, but NO FLOATING of any
higher levels, rather a merging of these levels into the insulating state. For
a given filling factor, only direct transitions between the insulating phase
and higher quantum Hall liquids are observed as a function of density. Finally,
we observe a peak in the critical resistivity around filling factor one.Comment: 4 pages, 4 figures, some changes in the tex
Diffusion in disordered systems under iterative measurement
We consider a sequence of idealized measurements of time-separation onto a discrete one-dimensional disordered system. A connection with Markov
chains is found. For a rapid sequence of measurements, a diffusive regime
occurs and the diffusion coefficient is analytically calculated. In a
general point of view, this result suggests the possibility to break the
Anderson localization due to decoherence effects. Quantum Zeno effect emerges
because the diffusion coefficient vanishes at the limit .Comment: 8 pages, 0 figures, LATEX. accepted in Phys.Rev.
Delocalization of states in two component superlattices with correlated disorder
Electron and phonon states in two different models of intentionally
disordered superlattices are studied analytically as well as numerically. The
localization length is calculated exactly and we found that it diverges for
particular energies or frequencies, suggesting the existence of delocalized
states for both electrons and phonons. Numerical calculations for the
transmission coefficient support the existence of these delocalized states.Comment: RevTeX, 12 pages, 2 PS figures adde
Raising rivals’ fixed costs
This article demonstrates that raising fixed costs can serve as a credible mechanism for a well placed firm to exclude its rivals. We identify a number of credible avenues, such as increased regulation, vexatious litigation and increased prices for essential inputs, through which such a firm can raise fixed costs. We show that for a wide range of oligopoly models this may be a profitable strategy, even if the firm’s own fixed costs are affected as much (or even more) than its rivals and even if it is less efficient. The resulting reduction in the number of firms in the market is detrimental to consumer welfare and hence worthy of scrutiny by competition and regulatory authorities
Delocalization in Continuous Disordered Systems
Continuous One-dimensional models supporting extended states are studied.
These delocalized statesoccur at well defined values of the energy and are
consequences of simple statistical correlation rules. We explicitly study
alloys of delta-barrier potentials as well as alloys and liquids of quantum
well as.The divergence of the localization length is studied and a critical
exponent 2/3 is found for the delta-barrier case, whereas for the quantum wells
we find an exponent of 2 or 2/3 depending on the well's parameters. These
results support the idea that correlations between random scattering sequences
break Anderson localization. We further calculate the conductance of disordered
superlattices. At the peak transmission the relative fluctuations of the
transmission coefficient are vanishing.Comment: 8 page
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