3,450 research outputs found
Topological phases in a two-dimensional lattice: Magnetic field versus spin-orbit coupling
In this work, we explore the rich variety of topological states that arise in
two-dimensional systems, by considering the competing effects of spin-orbit
couplings and a perpendicular magnetic field on a honeycomb lattice. Unlike
earlier approaches, we investigate minimal models in order to clarify the
effects of the intrinsic and Rashba spin-orbit couplings, and also of the
Zeeman splitting, on the quantum Hall states generated by the magnetic field.
In this sense, our work provides an interesting path connecting quantum Hall
and quantum spin Hall physics. First, we consider the properties of each term
individually and we analyze their similarities and differences. Secondly, we
investigate the subtle competitions that arise when these effects are combined.
We finally explore the various possible experimental realizations of our model.Comment: 19 pages, 15 figure
Arterial Oxygen Tension in Relation to Age in Hospital Subjects
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111097/1/j.1532-5415.1973.tb00840.x.pd
Energetics of Quantum Antidot States in Quantum Hall Regime
We report experiments on the energy structure of antidot-bound states. By
measuring resonant tunneling line widths as function of temperature, we
determine the coupling to the remote global gate voltage and find that the
effects of interelectron interaction dominate. Within a simple model, we also
determine the energy spacing of the antidot bound states, self consistent edge
electric field, and edge excitation drift velocity.Comment: 4 pages, RevTex, 5 Postscript figure
Topological phase transitions between chiral and helical spin textures in a lattice with spin-orbit coupling and a magnetic field
We consider the combined effects of large spin-orbit couplings and a
perpendicular magnetic field in a 2D honeycomb fermionic lattice. This system
provides an elegant setup to generate versatile spin textures propagating along
the edge of a sample. The spin-orbit coupling is shown to induce topological
phase transitions between a helical quantum spin Hall phase and a chiral
spin-imbalanced quantum Hall state. Besides, we find that the spin orientation
of a single topological edge state can be tuned by a Rashba spin-orbit
coupling, opening an interesting route towards quantum spin manipulation. We
discuss the possible realization of our results using cold atoms trapped in
optical lattices, where large synthetic magnetic fields and spin-orbit
couplings can be engineered and finely tuned. In particular, this system would
lead to the observation of a time-reversal-symmetry-broken quantum spin Hall
phase.Comment: 8 pages, 3 figures, Accepted in Europhys. Lett. (Dec 2011
The Surface of a Bose-Einstein Condensed Atomic Cloud
We investigate the structure and collective modes of a planar surface of a
trapped Bose-Einstein condensed gas at zero temperature. In the long-wavelength
limit we find a mode similar to the gravity wave on the surface of a fluid with
the frequency and the wavenumber related by . Here
is the force due to the confining potential at the surface and is the
particle mass. At shorter wavelengths we use a variational approach and find
corrections to of order . We demonstrate the usefulness
of the concept of an effective surface tension for describing both static and
dynamic properties of condensed atomic clouds.Comment: 8 pages, REVTEX, submitted to Phys. Rev.
Effects of resonant tunneling in electromagnetic wave propagation through a polariton gap
We consider tunneling of electromagnetic waves through a polariton band gap
of a 1-D chain of atoms. We analytically show that a defect embedded in the
structure gives rise to the resonance transmission at the frequency of a local
polariton state associated with the defect. Numerical Monte-Carlo simulations
are used to examine properties of the electromagnetic band arising inside the
polariton gap due to finite concentration of defects.Comment: 12 pages, 6 figures, RevTe
Obstructing extensions of the functor Spec to noncommutative rings
In this paper we study contravariant functors from the category of rings to
the category of sets whose restriction to the full subcategory of commutative
rings is isomorphic to the prime spectrum functor Spec. The main result reveals
a common characteristic of these functors: every such functor assigns the empty
set to M_n(C) for n >= 3. The proof relies, in part, on the Kochen-Specker
Theorem of quantum mechanics. The analogous result for noncommutative
extensions of the Gelfand spectrum functor for C*-algebras is also proved.Comment: 23 pages. To appear in Israel J. Math. Title was changed;
introduction was rewritten; old Section 2 was removed to streamline the
exposition; final section was rewritten to omit an error in the earlier proof
of Theorem 1.
Pairwise alignment incorporating dipeptide covariation
Motivation: Standard algorithms for pairwise protein sequence alignment make
the simplifying assumption that amino acid substitutions at neighboring sites
are uncorrelated. This assumption allows implementation of fast algorithms for
pairwise sequence alignment, but it ignores information that could conceivably
increase the power of remote homolog detection. We examine the validity of this
assumption by constructing extended substitution matrixes that encapsulate the
observed correlations between neighboring sites, by developing an efficient and
rigorous algorithm for pairwise protein sequence alignment that incorporates
these local substitution correlations, and by assessing the ability of this
algorithm to detect remote homologies. Results: Our analysis indicates that
local correlations between substitutions are not strong on the average.
Furthermore, incorporating local substitution correlations into pairwise
alignment did not lead to a statistically significant improvement in remote
homology detection. Therefore, the standard assumption that individual residues
within protein sequences evolve independently of neighboring positions appears
to be an efficient and appropriate approximation
Microscopic Study of Quantum Vortex-Glass Transition Field in Two-Dimensional Superconductors
The position of a field-tuned superconductor-insulator quantum transition
occuring in disordered thin films is examined within the mean field
approximation. Our calculation shows that the microscopic disorder-induced
reduction of the quantum transition point found experimentally cannot be
explained if the interplay between the disorder and an electron-electron
repulsive interaction is ignored. This work is presented as a microscopic basis
of an explanation (cond-mat/0105122) of resistive phenomena near the transition
field.Comment: 16 pages, 5 figures. To appear in J.Phys.Soc.Jp
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