450 research outputs found
Character of jet flows in mass-spectrometric interfaces at various pressures and chamber lengths
Samples-in particular, of bioorganic matter—are usually introduced into a mass spectrometer from atmosphere to high vacuum via a gasdynamic interface that represents a chamber with intermediate pressure or a system of chambers with gradually decreasing pressure. Transformation of the character of an expanding jet flow in a single-chamber interface has been studied as dependent on the chamber length and pressure. Knowledge of this character allows the system parameters to be most effectively used so as to ensure high ion transmission and decrease mass discriminatio
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]
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
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
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
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
Mechanism of fragmentation and atomization of molecular ions in gasdynamic transport cell
The fragmentation of molecular ions formed upon the electrospraying of a sample and transported through the gasdynamic system of a mass spectrometer equipped with an IESAP (Ion Extraction from Solution at Atmospheric Pressure) source has been experimentally studied. It is established that ion fragmentation in a Kantorowicz-Gray type cell takes place in the immediate vicinity of a skimmer port, apparently, as a result of collisions between ions (accelerated in an electric field) and stagnant gas. Molecular mechanisms of fragmentation are considered and it is concluded that this process can take place in a single ion-molecule collision even
Creation, doubling, and splitting, of vortices in intracavity second harmonic generation
We demonstrate generation and frequency doubling of unit charge vortices in a
linear astigmatic resonator. Topological instability of the double charge
harmonic vortices leads to well separated vortex cores that are shown to
rotate, and become anisotropic, as the resonator is tuned across resonance
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