675 research outputs found
Electromechanical Imaging of Biological Systems with Sub-10 nm Resolution
Electromechanical imaging of tooth dentin and enamel has been performed with
sub-10 nm resolution using piezoresponse force microscopy. Characteristic
piezoelectric domain size and local protein fiber ordering in dentin have been
determined. The shape of a single collagen fibril in enamel is visualized in
real space and local hysteresis loops are measured. Because of the ubiquitous
presence of piezoelectricity in biological systems, this approach is expected
to find broad application in high-resolution studies of a wide range of
biomaterials.Comment: 12 pages, 4 figures, submitted for publication in Appl. Phys. Let
Spin-to-Orbital Angular Momentum Conversion in Semiconductor Microcavities
We experimentally demonstrate a technique for the generation of optical beams
carrying orbital angular momentum using a planar semiconductor microcavity.
Despite being isotropic systems, the transverse electric - transverse magnetic
(TE-TM) polarization splitting featured by semiconductor microcavities allows
for the conversion of the circular polarization of an incoming laser beam into
the orbital angular momentum of the transmitted light field. The process
implies the formation of topological entities, a pair of optical half-vortices,
in the intracavity field
Quantized Rotation of Atoms From Photons with Orbital Angular Momentum
We demonstrate the coherent transfer of the orbital angular momentum of a
photon to an atom in quantized units of hbar, using a 2-photon stimulated Raman
process with Laguerre-Gaussian beams to generate an atomic vortex state in a
Bose-Einstein condensate of sodium atoms. We show that the process is coherent
by creating superpositions of different vortex states, where the relative phase
between the states is determined by the relative phases of the optical fields.
Furthermore, we create vortices of charge 2 by transferring to each atom the
orbital angular momentum of two photons.Comment: New version, 4 pages and 3 figures, accepted for publication in
Physical Review Letter
Infrared studies of a La_(0.67)Ca_(0.33)MnO_3 single crystal: Optical magnetoconductivity in a half-metallic ferromagnet
The infrared reflectivity of a La_(0.67)Ca_(0.33)MnO_3 single crystal is studied over a broad range of temperatures (78–340 K), magnetic fields (0–16 T), and wave numbers (20–9000cm^(-1)). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000cm-1 in the ferromagnetic state below the Curie temperature T_C=307K. Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near T_C
Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganite La_{0.7}Ca_{0.3}MnO_{3}
Spatially resolved tunneling spectroscopic studies of colossal
magnetoresistive (CMR) manganite (LCMO) epitaxial
films on substrate are investigated as
functions of temperature, magnetic field and spin polarization by means of
scanning tunneling spectroscopy. Systematic surveys of the tunneling spectra
taken with Pt/Ir tips reveal spatial variations on the length scale of a few
hundred nanometers in the ferromagnetic state, which may be attributed to the
intrinsic heterogeneity of the manganites due to their tendency towards phase
separation. The electronic heterogeneity is found to decrease either with
increasing field at low temperatures or at temperatures above all magnetic
ordering temperatures. On the other hand, spectra taken with Cr-coated tips are
consistent with convoluted electronic properties of both LCMO and Cr. In
particular, for temperatures below the magnetic ordering temperatures of both
Cr and LCMO, the magnetic-field dependent tunneling spectra may be
quantitatively explained by the scenario of spin-polarized tunneling in a
spin-valve configuration. Moreover, a low-energy insulating energy gap eV commonly found in the tunneling conductance spectra of bulk metallic
LCMO at may be attributed to a surface ferromagnetic insulating (FI)
phase, as evidenced by its spin filtering effect at low temperatures and
vanishing gap value above the Curie temperature. Additionally, temperature
independent pseudogap (PG) phenomena existing primarily along the boundaries of
magnetic domains are observed in the zero-field tunneling spectra. The PG
becomes strongly suppressed by applied magnetic fields at low temperatures when
the tunneling spectra of LCMO become highly homogeneous. These findings suggest
that the occurrence PG is associated with the electronic heterogeneity of the
manganites.Comment: 15 pages, 15 figures. Published in Physical Review B. Corresponding
author: Nai-Chang Yeh (E-mail: [email protected]
Infrared Studies of a La_{0.67}Ca_{0.33}MnO_3 Single Crystal: Optical Magnetoconductivity in a Half-Metallic Ferromagnet
The infrared reflectivity of a single crystal
is studied over a broad range of temperatures (78-340 K), magnetic fields (0-16
T), and wavenumbers (20-9000 cm). The optical conductivity gradually
changes from a Drude-like behavior to a broad peak feature near 5000 cm
in the ferromagnetic state below the Curie temperature . Various
features of the optical conductivity bear striking resemblance to recent
theoretical predictions based on the interplay between the double exchange
interaction and the Jahn-Teller electron-phonon coupling. A large optical
magnetoconductivity is observed near .Comment: 4 pages, 4 figures, Latex, PostScript; The 7th Joint MMM-Intermag
Conference,San Francisco, January 6-9, 1998; The Int. Conf. on Strongly
Correlated Electron Systems, Paris, July 15-18,199
Discontinuous Bifurcations under 2-DOF Vibroimpact System Moving
Dynamic behaviour of strongly nonlinear non-smooth discontinuous vibroimpact system isstudied. Under variation of system parameters we find the disconti nuousbi furcati onsthat are the dangerousones. It is phenomenon
unique to non-smooth systems with discontinuous right-hand side. We investigate the 2-DOF vibroimpact system by numerical parameter continuation method in conjunction with shooting and Newton-Raphson methods,
Wife simulate the impact by nonlinear contact interactive force according to Hertz's contact law. We find the discontinuous bifurcations by Floquet multipliers values. At such points set-valued Floquet multipliers cross the
unit circle by jump that istheir moduli becoming more than unit by jump. Wealso learn the bifurcation picture
change when the impact between system bodi es became the soft one due the change of system parameters, This
paper is the continuation of the previous works
Corrosion resistance of alloys of Hastelloy in chloroaluminate melts
The corrosion of Hastelloy S, Hastelloy X, Haynes 230, Hastelloy N, Hastelloy G35 and Hastelloy C2000 alloys was studied in KCl-AlCl3 melts at 550°С. The rates and the mechanisms of corrosion of the studied materials were determined. The processes taking place during the interaction between alloys and chloroaluminate melts were investigated
Formation of metallic magnetic clusters in a Kondo-lattice metal: Evidence from an optical study
Magnetic materials are usually divided into two classes: those with localised
magnetic moments, and those with itinerant charge carriers. We present a
comprehensive experimental (spectroscopic ellipsomerty) and theoretical study
to demonstrate that these two types of magnetism do not only coexist but
complement each other in the Kondo-lattice metal, Tb2PdSi3. In this material
the itinerant charge carriers interact with large localised magnetic moments of
Tb(4f) states, forming complex magnetic lattices at low temperatures, which we
associate with self-organisation of magnetic clusters. The formation of
magnetic clusters results in low-energy optical spectral weight shifts, which
correspond to opening of the pseudogap in the conduction band of the itinerant
charge carriers and development of the low- and high-spin intersite electronic
transitions. This phenomenon, driven by self-trapping of electrons by magnetic
fluctuations, could be common in correlated metals, including besides
Kondo-lattice metals, Fe-based and cuprate superconductors.Comment: 30 pages, 6 Figure
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