2,972 research outputs found
Finite-temperature Screening and the Specific Heat of Doped Graphene Sheets
At low energies, electrons in doped graphene sheets are described by a
massless Dirac fermion Hamiltonian. In this work we present a semi-analytical
expression for the dynamical density-density linear-response function of
noninteracting massless Dirac fermions (the so-called "Lindhard" function) at
finite temperature. This result is crucial to describe finite-temperature
screening of interacting massless Dirac fermions within the Random Phase
Approximation. In particular, we use it to make quantitative predictions for
the specific heat and the compressibility of doped graphene sheets. We find
that, at low temperatures, the specific heat has the usual normal-Fermi-liquid
linear-in-temperature behavior, with a slope that is solely controlled by the
renormalized quasiparticle velocity.Comment: 9 pages, 5 figures, Submitted to J. Phys.
Thermodynamic Properties of XXZ model in a Transverse Field
We have numerically studied the thermodynamic properties of the spin 1/2 XXZ
chain in the presence of a transverse (non commuting) magnetic field. The
thermal, field dependence of specific heat and correlation functions for chains
up to 20 sites have been calculated. The area where the specific heat decays
exponentially is considered as a measure of the energy gap. We have also
obtained the exchange interaction between chains in a bulk material using the
random phase approximation and derived the phase diagram of the three
dimensional material with this approximation. The behavior of the structure
factor at different momenta verifies the antiferromagnetic long range order in
y-direction for the three dimensional case. Moreover, we have concluded that
the Low Temperature Lanczos results [M. Aichhorn et al., Phys. Rev. B 67,
161103(R) (2003)] are more accurate for low temperatures and closer to the full
diagonalization ones than the results of Finite Temperature Lanczos Method [J.
Jaklic and P. Prelovsek, Phys. Rev. B 49, 5065 (1994)].Comment: 7 pages, 10 eps figure
Plasma diagnostic of a solar prominence from hydrogen and helium resonance lines
We present the first comparison of profiles of H et He resonance lines
observed by SUMER with theoretical profiles computed with our non-LTE radiative
transfer code. We use the H I Lyman-beta, H I Lyman-epsilon, and He I 584 A
lines. Our code allows us to obtain the plasma parameters in prominences in
conjunction with a multi-line, multi-element set of observations. The plasma
temperature in the prominence core is ~ 8600 K and the pressure is 0.03
dyn/cm^2. The Ly-beta line is formed in a higher temperature region (more than
11000 K).Comment: 2 pages, 2 color figures. Proceedings of SF2A, Semaine de
l'Astrophysique Francaise, Journees de la SF2A 2006, Pari
Aerospace Medicine and Biology: A continuing bibliography (supplement 229)
This bibliography lists 109 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1982
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