10,307 research outputs found
Interactions between Membrane Inclusions on Fluctuating Membranes
We model membrane proteins as anisotropic objects characterized by
symmetric-traceless tensors and determine the coupling between these
order-parameters and membrane curvature. We consider the interactions between
transmembrane proteins that respect up-down (reflection) symmetry of bilayer
membranes and that have circular or non-circular cross-sectional areas in the
tangent-plane of membranes. Using a field theoretic approach, we find
non-entropic interactions between reflection-symmetry-breaking
transmembrane proteins with circular cross-sectional area and entropic
interactions between transmembrane proteins with circular
cross-section that do not break up-down symmetry in agreement with previous
calculations. We also find anisotropic interactions between
reflection-symmetry-conserving transmembrane proteins with non-circular
cross-section, anisotropic interactions between
reflection-symmetry-breaking transmembrane proteins with non-circular
cross-section, and non-entropic many-particle interactions among
non-transmembrane proteins. For large , these interactions might provide the
dominant force inducing aggregation of the membrane proteins.Comment: REVTEX, 29 pages with 4 postscript figures compressed using uufiles.
Introduction and Discussion sections revised. To appear in J. Phys. France I
(September
Disclination Asymmetry in Deformable Hexatic Membranes and the Kosterlitz-Thouless Transitions
A disclination in a hexatic membrane favors the development of Gaussian
curvature localized near its core. The resulting global structure of the
membrane has mean curvature, which is disfavored by curvature energy. Thus a
membrane with an isolated disclination undergoes a buckling transition from a
flat to a buckled state as the ratio of the bending rigidity
to the hexatic rigidity is decreased. In this paper we
calculate the buckling transition and the energy of both a positive and a
negative disclination. A negative disclination has a larger energy and a
smaller critical value of at buckling than does a positive
disclination. We use our results to obtain a crude estimate of the
Kosterlitz-Thouless transition temperature in a membrane. This estimate is
higher than the transition temperature recently obtained by the authors in a
renormalization calculation.Comment: REVTEX, 16 pages with 5 postscript figures compressed using uufiles.
Accepted for publication in J. Phys. France
Sample-specific and Ensemble-averaged Magnetoconductance of Individual Single-Wall Carbon Nanotubes
We discuss magnetotransport measurements on individual single-wall carbon
nanotubes with low contact resistance, performed as a function of temperature
and gate voltage. We find that the application of a magnetic field
perpendicular to the tube axis results in a large magnetoconductance of the
order of e^2/h at low temperature. We demonstrate that this magnetoconductance
consists of a sample-specific and of an ensemble-averaged contribution, both of
which decrease with increasing temperature. The observed behavior resembles
very closely the behavior of more conventional multi-channel mesoscopic wires,
exhibiting universal conductance fluctuations and weak localization. A
theoretical analysis of our experiments will enable to reach a deeper
understanding of phase-coherent one-dimensional electronic motion in SWNTs.Comment: Replaced with published version. Minor changes in tex
Controlling spin in an electronic interferometer with spin-active interfaces
We consider electronic current transport through a ballistic one-dimensional
quantum wire connected to two ferromagnetic leads. We study the effects of the
spin-dependence of interfacial phase shifts (SDIPS) acquired by electrons upon
scattering at the boundaries of the wire. The SDIPS produces a spin splitting
of the wire resonant energies which is tunable with the gate voltage and the
angle between the ferromagnetic polarizations. This property could be used for
manipulating spins. In particular, it leads to a giant magnetoresistance effect
with a sign tunable with the gate voltage and the magnetic field applied to the
wire.Comment: 5 pages, 3 figures. to be published in Europhysics Letter
Spin-dependent Quantum Interference in Single-Wall Carbon Nanotubes with Ferromagnetic Contacts
We report the experimental observation of spin-induced magnetoresistance in
single-wall carbon nanotubes contacted with high-transparency ferromagnetic
electrodes. In the linear regime the spin-induced magnetoresistance oscillates
with gate voltage in quantitative agreement with calculations based on a
Landauer-Buttiker model for independent electrons. Consistent with this
interpretation, we find evidence for bias-induced oscillation in the
spin-induced magnetoresistance signal on the scale of the level spacing in the
nanotube. At higher bias, the spin-induced magnetoresistance disappears because
of a sharp decrease in the effective spin-polarization injected from the
ferromagnetic electrodes.Comment: Replaced with published versio
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