1,390 research outputs found
Density of a gas of spin polarized fermions in a magnetic field
For a fermion gas with equally spaced energy levels that is subjected to a
magnetic field, the particle density is calculated. The derivation is based on
the path integral approach for identical particles, in combination with the
inversion techniques for the generating function of the static response
functions. Explicit results are presented for the ground state density as a
function of the magnetic field with a number of particles ranging from 1 to 45.Comment: 9 pages, 8 figures; To appear in Phys. Rev. E on December 1, 2000;
e-mail addresses: [email protected], [email protected],
[email protected], [email protected]
Interplay of Spin and Lattice Degrees of Freedom in the Frustrated Antiferromagnet CdCr_2O_4: High-field and Temperature Induced Anomalies of the Elastic Constants
Temperature and magnetic field studies of the elastic constants of the
chromium spinel CdCr_2O_4 show pronounced anomalies related to strong
spin-phonon coupling in this frustrated antiferromagnet. A detailed comparison
of the longitudinal acoustic mode propagating along the [111] direction with
theory based on an exchange-striction mechanism leads to an estimate of the
strength of the magneto-elastic interaction. The derived spin-phonon coupling
constant is in good agreement with previous determinations based on infrared
absorption. Further insight is gained from intermediate and high magnetic field
experiments in the field regime of the magnetization plateau. The role of the
antisymmetric Dzyaloshinskii-Moriya interaction discussed and we compare the
spin-phonon coupling in CdCr_2O_4 in both the ordered and disordered states.Comment: 12 pages, 8 figures; Appendix added,To appear in Phys Rev.
Magnetic bound states in the quarter-filled ladder system }
Raman scattering in the quarter-filled spin ladder system alpha'-NaV_2O_5
shows in the dimerized singlet ground state () an unexpected
sequence of three magnetic bound states. Our results suggest that the recently
proposed mapping onto an effective spin chain for has to be given
up in favor of the full topology and exchange paths of a ladder in the
dimerized phase for . As the new ground state we propose a dynamic
superposition of energetically nearly degenerate dimer configurations on the
ladder.Comment: 5 pages, 4 figures, to be published in PRB, brief reports, Dec. 199
Anomalous optical phonons in FeTe pnictides: spin state, magnetic order, and lattice anharmonicity
Polarized Raman-scattering spectra of non-superconducting, single-crystalline
FeTe are investigated as function of temperature. We have found a relation
between the magnitude of ordered magnetic moments and the linewidth of A1g
phonons at low temperatures. This relation is attributed to the intermediate
spin state (S=1) and the orbital degeneracy of the Fe ions. Spin-phonon
coupling constants have been estimated based on microscopic modeling using
density-functional theory and analysis of the local spin density. Our
observations show the importance of orbital degrees of freedom for the Fe-based
superconductors with large ordered magnetic moments, while small magnetic
moment of Fe ions in some iron pnictides reflects the low spin state of Fe ions
in those systems.Comment: 17 pages, 3 figure
Ground state and optical conductivity of interacting polarons in a quantum dot
The ground-state energy, the addition energies and the optical absorption
spectra are derived for interacting polarons in parabolic quantum dots in three
and two dimensions. A path integral formalism for identical particles is used
in order to take into account the fermion statistics. The approach is applied
to both closed-shell and open-shell systems of interacting polarons. Using a
generalization of the Jensen-Feynman variational principle, the ground-state
energy of a confined N-polaron system is analyzed as a function of N and of the
electron-phonon coupling constant. As distinct from the few-electron systems
without the electron-phonon interaction, three types of spin polarization are
possible for the ground state of the few-polaron systems: (i) a spin-polarized
state, (ii) a state where the spin is determined by Hund's rule, (iii) a state
with the minimal possible spin. A transition from a state fulfilling Hund's
rule, to a spin-polarized state occurs when decreasing the electron density. In
the strong-coupling limit, the system of interacting polarons turns into a
state with the minimal possible spin. These transitions should be
experimentally observable in the optical absorption spectra of quantum dots.Comment: 33 pages, 9 figures, E-mail addresses: [email protected],
[email protected], [email protected], [email protected],
accepted for Phys. Rev.
Bulk antiferromagnetism in single crystals
Susceptibility, specific heat, and muon spin rotation measurements on
high-quality single crystals of have revealed bulk
antiferromagnetism with N\'{e}el temperature K and an
ordered moment perpendicular to the layers. The magnetic order
encompasses nearly 100% of the crystal volume. The susceptibility exhibits a
broad peak around 30 K, characteristic of two-dimensional antiferromagnetic
fluctuations. The in-plane resistivity is metallic at high temperatures and
exhibits a minimum at .Comment: published versio
Correlations in a Confined gas of Harmonically Interacting Spin-Polarized Fermions
For a fermion gas with equally spaced energy levels, the density and the pair
correlation function are obtained. The derivation is based on the path integral
approach for identical particles and the inversion of the generating functions
for both static responses. The density and the pair correlation function are
evaluated explicitly in the ground state of a confined fermion system with a
number of particles ranging from 1 to 220 and filling the Fermi level
completely.Comment: 11 REVTEX pages, 3 postscript figures. Accepted for publication in
Phys. Rev. E, Vol. 58 (August 1, 1998
Thermodynamics of Coupled Identical Oscillators within the Path Integral Formalism
A generalization of symmetrized density matrices in combination with the
technique of generating functions allows to calculate the partition function of
identical particles in a parabolic confining well. Harmonic two-body
interactions (repulsive or attractive) are taken into account. Also the
influence of a homogeneous magnetic field, introducing anisotropy in the model,
is examined. Although the theory is developed for fermions and bosons, special
attention is payed to the thermodynamic properties of bosons and their
condensation.Comment: 13 REVTEX pages + 9 postscript figure
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