189 research outputs found
Ando, Lavrov, and Segawa Reply
Authors' Reply to the Comment by Janossy et al. [cond-mat/0005275] on our
article, "Magnetoresistance Anomalies in Antiferromagnetic
YBa_{2}Cu_{3}O_{6+x}: Fingerprints of Charged Stripes" [cond-mat/9905071, Phys.
Rev. Lett. 83, 2813 (1999)].Comment: 1 page, 1 figure, accepted for publication in PR
Origin of the ESR spectrum in the Prussian Blue analogue RbMn[Fe(CN)6]*H2O
We present an ESR study at excitation frequencies of 9.4 GHz and 222.4 GHz of
powders and single crystals of a Prussian Blue analogue (PBA),
RbMn[Fe(CN)6]*H2O in which Fe and Mn undergoes a charge transfer transition
between 175 and 300 K. The ESR of PBA powders, also reported by Pregelj et al.
(JMMM, 316, E680 (2007)) is assigned to cubic magnetic clusters of Mn2+ ions
surrounding Fe(CN)6 vacancies. The clusters are well isolated from the bulk and
are superparamagnetic below 50 K. In single crystals various defects with lower
symmetry are also observed. Spin-lattice relaxation broadens the bulk ESR
beyond observability. This strong spin relaxation is unexpected above the
charge transfer transition and is attributed to a mixing of the Mn3+ - Fe2+
state into the prevalent Mn2+ - Fe3+ state.Comment: 5 pages, 4 figures, submitted to PR
Magnetic resonance in the antiferromagnetic and normal state of NH_3K_3C_60
We report on the magnetic resonance of NH_3K_3C_60 powders in the frequency
range of 9 to 225 GHz. The observation of an antiferromagnetic resonance below
the phase transition at 40 K is evidence for an antiferromagnetically ordered
ground state. In the normal state, above 40 K, the temperature dependence of
the spin-susceptibilty measured by ESR agrees with previous static measurements
and is too weak to be explained by interacting localized spins in an insulator.
The magnetic resonance line width has an unusual magnetic-field dependence
which is large and temperature independent in the magnetically ordered state
and decreases rapidly above the transition. These observations agree with the
suggestion that NH_3K_3C_60 is a metal in the normal state and undergoes a
Mott-Hubbard metal to insulator transition at 40 K.Comment: 4 pages, 5 figures. Submitted to Phys. Rev.
Generation of Multiple Circular Walls on a Thin Film of Nematic Liquid Crystal by Laser Scanning
We found that multiple circular walls (MCW) can be generated on a thin film
of a nematic liquid crystal through a spiral scanning of a focused IR laser.
The ratios between radii of adjacent rings of MCW were almost constant. These
constant ratios can be explained theoretically by minimization of the Frank
elastic free energy of nematic medium. The director field on a MCW exhibits
chiral symmetry-breaking although the elastic free energies of both chiral MCWs
are degenerated, i.e., the director on a MCW can rotate clockwise or
counterclockwise along the radial direction.Comment: 10 pages, 5 figures. Submitted to Chemical Physics Letters 2nd
Editio
Antiferromagnetic domain walls in lightly doped layered cuprates
Recent ESR data shows rotation of the antiferromagnetic (AF) easy axis in
lightly doped layered cuprates upon lowering the temperature. We account for
the ESR data and show that it has significant implications on spin and charge
ordering according to the following scenario: In the high temperature phase AF
domain walls coincide with (110) twin boundaries of an orthorhombic phase. A
magnetic field leads to annihilation of neighboring domain walls resulting in
antiphase boundaries. The latter are spin carriers, form ferromagnetic lines
and may become charged in the doped system. However, hole ordering at low
temperatures favors the (100) orientation, inducing a pi/4 rotation in the AF
easy axis. The latter phase has twin boundaries and AF domain walls in (100)
planes.Comment: 4 pages, 3 figures (1 eps). v2: no change in content, Tex shadow
problem cleare
Spin-stretching modes in anisotropic magnets: spin-wave excitations in the multiferroic Ba2CoGe2O7
We studied spin excitations of the multiferroic Ba2CoGe2O7 in high magnetic
fields up to 33 T. In the electron spin resonance and far infrared absorption
spectra we found several spin excitations beyond the two conventional magnon
modes expected for such a two-sublattice antiferromagnet. We show that a
multi-boson spin-wave theory can capture these unconventional modes, that
include spin-stretching modes associated with an oscillating magnetic dipole
(or only quadrupole) moment. The lack of the inversion symmetry allows these
modes to become electric dipole active. We expect that the spin-stretching
modes can be generally observed in inelastic neutron scattering and light
absorption experiments in a broad class of ordered S > 1/2 spin systems with
strong single-ion anisotropy and/or non-centrosymmetric lattice structure.Comment: 5+4 pages, 3 figures, supplement added, manuscript revise
Fluctuating-friction molecular motors
We show that the correlated stochastic fluctuation of the friction
coefficient can give rise to long-range directional motion of a particle
undergoing Brownian random walk in a constant periodic energy potential
landscape. The occurrence of this motion requires the presence of two
additional independent bodies interacting with the particle via friction and
via the energy potential, respectively, which can move relative to each other.
Such three-body system generalizes the classical Brownian ratchet mechanism,
which requires only two interacting bodies. In particular, we describe a simple
two-level model of fluctuating-friction molecular motor that can be solved
analytically. In our previous work [M.K., L.M and D.P. 2000 J. Nonlinear Opt.
Phys. Mater. vol. 9, 157] this model has been first applied to understanding
the fundamental mechanism of the photoinduced reorientation of dye-doped liquid
crystals. Applications of the same idea to other fields such as molecular
biology and nanotechnology can however be envisioned. As an example, in this
paper we work out a model of the actomyosin system based on the
fluctuating-friction mechanism.Comment: to be published in J. Physics Condensed Matter
(http://www.iop.org/Journals/JPhysCM
Low temperature fullerene encapsulation in single wall carbon nanotubes: synthesis of N@C@SWCNT
High filling of single wall carbon nanotubes (SWCNT) with C and
C fullerenes in solvent is reported at temperatures as low as 69
C. A 2 hour long refluxing in n-hexane of the mixture of the fullerene
and SWCNT results in a high yield of C,C@SWCNT, fullerene peapod,
material. The peapod filling is characterized by TEM, Raman and electron energy
loss spectroscopy and X-ray scattering. We applied the method to synthesize the
temperature sensitive (N@C:C)@SWCNT as proved by electron spin
resonance spectroscopy. The solvent prepared peapod samples can be transformed
to double walled nanotubes enabling a high yield and industrially scalable
production of DWCNT
Gravity as Archimedes' thrust and a bifurcation in that theory
Euler's interpretation of Newton's gravity (NG) as Archimedes' thrust in a
fluid ether is presented in some detail. Then a semi-heuristic mechanism for
gravity, close to Euler's, is recalled and compared with the latter. None of
these two "gravitational ethers" can obey classical mechanics. This is logical
since the ether defines the very reference frame, in which mechanics is
defined. This concept is used to build a scalar theory of gravity: NG
corresponds to an incompressible ether, a compressible ether leads to
gravitational waves. In the Lorentz-Poincar\'e version, special relativity is
compatible with the ether, but, with the heterogeneous ether of gravity, it
applies only locally. A correspondence between metrical effects of uniform
motion and gravitation is assumed, yet in two possible versions (one is new).
Dynamics is based on a (non-trivial) extension of Newton's second law. The
observational status for the theory with the older version of the
correspondence is summarized.Comment: 24 pages, invited contribution to the Franco Selleri Festschrift, to
appear in Found. Physics. v3: Endnote 45 on absolute simultaneity improved
(formerly footnote 6: class file changed to revtex4), a few references
updated (and now with titles). v2: minor correction in subsect. 3.2, some
wording improvements, and a few references adde
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