824 research outputs found
The giant effect of magnetic ordering on a sound velocity in a sigma-Fe55Cr45 alloy
We studied atomic dynamics of sigma-Fe(100-x)Cr(x) (x=45 and 49.5) alloys
using nuclear inelastic scattering of synchrotron radiation. For the
sigma-Fe55Cr45 alloy, the derived reduced iron-partial density of phonon states
reveal a huge difference in the low-energy region between magnetic and
paramagnetic states. The latter implies a ca.36% increase of the sound velocity
in the magnetic phase, which testifies to a magnetically-induced hardening of
the lattice.Comment: 8 pages, 3 figures, 17 reference
General properties of quantum optical systems in a strong field limit
We investigate the dynamics of an arbitrary atomic system (n-level atoms or many n-level atoms) interacting with a resonant quantized mode of an em field. If the initial field state is a coherent state with a large photon number then the system dynamics possesses some general features, independently of the particular structure of the atomic system. Namely, trapping states, factorization of the wave function, collapses and revivals of the atomic energy oscillations are discussed
Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure
The temperature and pressure dependence of the partial density of phonon
states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear
inelastic scattering (NIS). The high energy resolution allows for a detailed
observation of spectral properties. A sharpening of the optical phonon modes
and shift of all spectral features towards higher energies by ~4% with
decreasing temperature from 296 K to 10 K was found. However, no detectable
change at the tetragonal - orthorhombic phase transition around 100 K was
observed. Application of a pressure of 6.7 GPa, connected with an increase of
the superconducting temperature from 8 K to 34 K, results in an increase of the
optical phonon mode energies at 296 K by ~12%, and an even more pronounced
increase for the lowest-lying transversal acoustic mode. Despite these strong
pressure-induced modifications of the phonon-DOS we conclude that the
pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the
framework of classical electron-phonon coupling. This result suggests the
importance of spin fluctuations to the observed superconductivity
A relativistic model of the -dimensional singular oscillator
Exactly solvable -dimensional model of the quantum isotropic singular
oscillator in the relativistic configurational -space is proposed. It
is shown that through the simple substitutions the finite-difference equation
for the -dimensional singular oscillator can be reduced to the similar
finite-difference equation for the relativistic isotropic three-dimensional
singular oscillator. We have found the radial wavefunctions and energy spectrum
of the problem and constructed a dynamical symmetry algebra.Comment: 8 pages, accepted for publication in J. Phys.
Entropy as a function of Geometric Phase
We give a closed-form solution of von Neumann entropy as a function of
geometric phase modulated by visibility and average distinguishability in
Hilbert spaces of two and three dimensions. We show that the same type of
dependence also exists in higher dimensions. We also outline a method for
measuring both the entropy and the phase experimentally using a simple
Mach-Zehnder type interferometer which explains physically why the two concepts
are related.Comment: 19 pages, 7 figure
Cavity Dynamical Casimir Effect in the presence of a three-level atom
We consider the scenario in which a damped three-level atom in the ladder or
V configurations is coupled to a single cavity mode whose vacuum state is
amplified by dint of the dynamical Casimir effect. We obtain approximate
analytical expressions and exact numerical results for the time-dependent
probabilities, demonstrating that the presence of the third level modifies the
photon statistics and its population can serve as a witness of photon
generation from vacuum.Comment: 7 pages, 4 figure
Measuring velocity of sound with nuclear resonant inelastic x-ray scattering
Nuclear resonant inelastic x-ray scattering is used to measure the projected
partial phonon density of states of materials. A relationship is derived
between the low-energy part of this frequency distribution function and the
sound velocity of materials. Our derivation is valid for harmonic solids with
Debye-like low-frequency dynamics. This method of sound velocity determination
is applied to elemental, composite, and impurity samples which are
representative of a wide variety of both crystalline and noncrystalline
materials. Advantages and limitations of this method are elucidated
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