21 research outputs found
Field-asymmetric transverse magnetoresistance in a nonmagnetic quantum-size structure
A new phenomenon is observed experimentally in a heavily doped asymmetric
quantum-size structure in a magnetic field parallel to the quantum-well layers
- a transverse magnetoresistance which is asymmetric in the field (there can
even be a change in sign) and is observed in the case that the structure has a
built-in lateral electric field. A model of the effect is proposed. The
observed asymmetry of the magnetoresistance is attributed to an additional
current contribution that arises under nonequilibrium conditions and that is
linear in the gradient of the electrochemical potential and proportional to the
parameter characterizing the asymmetry of the spectrum with respect to the
quasimomentum.Comment: 10 pages, 5 figures. For correspondence, mail to
[email protected]
Temperature dependence of electric resistance and magnetoresistance of pressed nanocomposites of multilayer nanotubes with the structure of nested cones
Bulk samples of carbon multilayer nanotubes with the structure of nested
cones (fishbone structure) suitable for transport measurements, were prepared
by compressing under high pressure (~25 kbar) a nanotube precursor synthesized
through thermal decomposition of polyethylene catalyzed by nickel. The
structure of the initial nanotube material was studied using high-resolution
transmission electron microscopy. In the low-temperature range (4.2 - 100 K)
the electric resistance of the samples changes according to the law ln \rho ~
(T_0/T)^{1/3}, where T_0 ~ 7 K. The measured magnetoresistance is quadratic in
the magnetic field and linear in the reciprocal temperature. The measurements
have been interpreted in terms of two-dimensional variable-range hopping
conductivity. It is suggested that the space between the inside and outside
walls of nanotubes acts as a two-dimensional conducting medium. Estimates
suggest a high value of the density of electron states at the Fermi level of
about 5 10^{21} eV^{-1} cm^{-3}.Comment: 8 pages, 4 figures. EM photographic images on figures 1a, 1b, 1c
attached as JPG files. For correspondence mail to [email protected]
Graphene as a quantum surface with curvature-strain preserving dynamics
We discuss how the curvature and the strain density of the atomic lattice
generate the quantization of graphene sheets as well as the dynamics of
geometric quasiparticles propagating along the constant curvature/strain
levels. The internal kinetic momentum of Riemannian oriented surface (a vector
field preserving the Gaussian curvature and the area) is determined.Comment: 13p, minor correction