21,488 research outputs found
Partial inner product spaces: Some categorical aspects
We make explicit in terms of categories a number of statements from the
theory of partial inner product spaces (PIP spaces) and operators on them.
In particular, we construct sheaves and cosheaves of operators on certain PIP
spaces of practical interest.Comment: 21 page
Peculiar Nature of Snake States in Graphene
We study the dynamics of the electrons in a non-uniform magnetic field
applied perpendicular to a graphene sheet in the low energy limit when the
excitation states can be described by a Dirac type Hamiltonian. We show that as
compared to the two-dimensional electron gas (2DEG) snake states in graphene
exibit peculiar properties related to the underlying dynamics of the Dirac
fermions. The current carried by snake states is locally uncompensated even if
the Fermi energy lies between the first non-zero energy Landau levels of the
conduction and valence bands. The nature of these states is studied by
calculating the current density distribution. It is shown that besides the
snake states in finite samples surface states also exist.Comment: 4 pages, 5 figure
Suppression of Giant Magnetoresistance by a superconducting contact
We predict that current perpendicular to the plane (CPP) giant
magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed
when one of the contacts is superconducting. This is a consequence of a
superconductivity-induced magneto-resistive (SMR) effect, whereby the
conductance of the ferromagnetically aligned state is drastically reduced by
superconductivity. To demonstrate this effect, we compute the GMR ratio of
clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd
tight binding Hamiltonian. By analyzing a simpler model with two orbitals per
site, we also show that the suppression survives in the presence of elastic
scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR
Why some fields might be rectangular: an exploration of agricultural landscapes between pre-capitalist and capitalist modes of production
This article is a preliminary investigation of possible spatial form which starts by rejecting the idea that spatial theory can be built from assumptions of isomorphism. It examines spatial form in high potential ridge valley areas which are densely populated, and identifies the transition in land configuration for pre-capitalist to capitalist modes of production. In building the argument simple geometric patterns that differentiate from the model are postulated. The basic drivers of the differing spatial systems are essentially the superstructural legal conditions which are postulated as a moving from communal, customary law to individual statutory property rights
Procyon-A and Eta-Bootis: Observational Frequencies Analyzed by the Local-Wave Formalism
In the present analysis of Procyon-A and Eta-Bootis, we use the local-wave
formalism which, despite its lack of precision inherent to any semi-analytical
method, uses directly the model profile without any modification when
calculating the acoustic mode eigenfrequencies. These two solar-like stars
present steep variations toward the center due to the convective core
stratification, and toward the surface due to the very thin convective zone.
Based on different boundary conditions, the frequencies obtained with this
formalism are different from that of the classical numerical calculation. We
point out that (1) the frequencies calculated with the local-wave formalism
seem to agree better with observational ones. All the frequencies detected with
a good confident level including those classified as 'noise' find an
identification, (2) some frequencies can be clearly identified here as
indications of the core limit.Comment: SOHO 18 / GONG 2006 / HELAS I Meetin
Quantum-limited mass flow of liquid He
We consider theoretically the possibility of observing unusual quantum fluid
behavior in liquid He and solutions of He in He systems
confined to nano-channels. In the case of pure ballistic flow at very low
temperature conductance will be quantized in units of . We show that
these steps should be sensitive to increases in temperature. We also use of a
random scattering matrix simulation to study flow with diffusive wall
scattering. Universal conductance fluctuations analogous to those seen in
electron systems should then be observable. Finally we consider the possibility
of the cross-over to a one-dimensional system at sufficiently low temperature
where the system could form a Luttinger liquid
Superconducting Proximity Effect and Universal Conductance Fluctuations
We examine universal conductance fluctuations (UCFs) in mesoscopic
normal-superconducting-normal (N-S-N) structures using a numerical solution of
the Bogoliubov - de Gennes equation. We discuss two cases depending on the
presence (``open'' structure) or absence (``closed'' structure) of
quasiparticle transmission. In contrast to N-S structures, where the onset of
superconductivity increases fluctuations, we find that UCFs are suppressed by
superconductivity for N-S-N structures. We demonstrate that the fluctuations in
``open'' and ``closed'' structures exhibit distinct responses to an applied
magnetic field and to an imposed phase variation of the superconducting order
parameter.Comment: (4 pages, 5 figures). Corrected typos in equations, added references,
changed Fig. 5 and its discussions. Phys. Rev. B, accepted for publicatio
Overcoming decoherence in the collapse and revival of spin Schr\"odinger cats
In addition to being a very interesting quantum phenomenon, Schr\"odinger cat
swapping has the potential for application in the preparation of quantum states
that could be used in metrology and other quantum processing. We study in
detail the effects of field decoherence on a cat-swapping system comprising a
set of identical qubits, or spins, all coupled to a field mode. We demonstrate
that increasing the number of spins actually mitigates the effects of field
decoherence on the collapse and revival of a spin Schr\"odinger cat, which
could be of significant utility in quantum metrology and other quantum
processing.Comment: 4 pages, 2 figure
Giant Backscattering Peak in Angle-Resolved Andreev Reflection
It is shown analytically and by numerical simulation that the angular
distribution of Andreev reflection by a disordered normal-metal --
superconductor junction has a narrow peak at the angle of incidence. The peak
is higher than the well-known coherent backscattering peak in the normal state,
by a large factor G/G_0 (where G is the conductance of the junction and
G_0=2e^2/h). The enhanced backscattering can be detected by means of ballistic
point contacts.Comment: Instituut-Lorentz, Leiden, The Netherlands, 4 pages, REVTeX-3.0, 3
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