548 research outputs found
Electronic susceptibilities in systems with anisotropic Fermi surfaces
The low temperature dependence of the spin and charge susceptibilities of an
anisotropic electron system in two dimensions is analyzed. It is shown that the
presence of inflection points at the Fermi surface leads, generically, to a dependence, and a more singular behavior, ,
is also possible. Applications to quasi two-dimensional materials are
discussed.Comment: 8 pages, 5 figures, revtex 4 styl
Leading Temperature Corrections to Fermi Liquid Theory in Two Dimensions
We calculate the basic parameters of the Fermi Liquid: the scattering vertex,
the Landau interaction function, the effective mass, and physical
susceptibilities for a model of two-dimensional (2D) fermions with a short
ranged interaction at non-zero temperature. The leading temperature dependences
of the spin components of the scattering vertex, the Landau function, and the
spin susceptibility are found to be linear. T-linear terms in the effective
mass and in the ``charge-sector''- quantities are found to cancel to second
order in the interaction, but the cancellation is argued not to be generic. The
connection with previous studies of the 2D Fermi-Liquid parameters is
discussed.Comment: 4 pages, 1 figur
Insulator-to-metal transition in Kondo insulators under strong magnetic field
Magnetization curve and changes of the single-particle excitation spectra by
magnetic field are calculated for the periodic Anderson model at half-filling
in infinite spatial dimension by using the exact diagonalization method. It is
found that the field-induced insulator-to-metal transition occurs at a critical
field , which is of the order of the single ion Kondo temperature. The
transition is of first order, but could be of second order in the infinite
system size limit. These results are compared with the experiments on the Kondo
insulator YbB.Comment: 11 pages, REVTEX, no figures; 7 figures available on request; To
appear in Phys. Rev. B, Mar.15, 199
Weak-coupling expansions for the attractive Holstein and Hubbard models
Weak-coupling expansions (conserving approximations) are carried out for the
attractive Holstein and Hubbard models (on an infinite-dimensional hypercubic
lattice) that include all bandstructure and vertex correction effects. Quantum
fluctuations are found to renormalize transition temperatures by factors of
order unity, but may be incorporated into the superconducting channel of
Migdal-Eliashberg theory by renormalizing the phonon frequency and the
interaction strength.Comment: 10 pages, (five figures available from the author by request) typeset
with ReVTeX, preprint NSF-ITP-93-10
A porous fibrous hyperelastic damage model for human periodontal ligament: Application of a microcomputerized tomography finite element model
The periodontal ligament (PDL) is a soft biological tissue that connects the tooth with the trabecular bone of the mandible. It plays a key role in load transmission and is primarily responsible for bone resorption and most common periodontal diseases. Although several numerical studies have analysed the biomechanical response of the PDL, most did not consider its porous fibrous structure, and only a few analysed damage to the PDL. This study presents an innovative numerical formulation of a porous fibrous hyperelastic damage material model for the PDL. The model considers two separate softening phenomena: fibre alignment during loading and fibre rupture. The parameters for the material model characterization were fitted using experimental data from the literature. Furthermore, the experimental tests used for characterization were computationally modelled to verify the material parameters. A finite element model of a portion of a human mandible, obtained by microcomputerized tomography, was developed, and the proposed constitutive model was implemented for the PDL. Our results confirm that damage to the PDL may occur mainly because of overpressure of the interstitial fluid, while large forces must be applied to damage the PDL fibrous network. Moreover, this study clarifies some aspects of the relationship between PDL damage and the bone remodelling process
Study of Intrinsic Spin Hall Effect and Orbital Hall Effect in 4d- and 5d- Transition Metals
We study the intrinsic spin Hall conductivity (SHC) in various
-transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d-transition metals
(Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory
tight-binding model, which enables us to perform quantitatively reliable
analysis. In each metal, the obtained intrinsic SHC is independent of
resistivity in the low resistive regime ()
whereas it decreases in proportion to in the high resistive regime.
In the low resistive regime, the SHC takes a large positive value in Pt and Pd,
both of which have approximately nine -electrons per ion (). On the
other hand, the SHC takes a large negative value in Ta, Nb, W, and Mo where
. In transition metals, a conduction electron acquires the
trajectory-dependent phase factor that originates from the atomic wavefunction.
This phase factor, which is reminiscent of the Aharonov-Bohm phase, is the
origin of the SHC in paramagnetic metals and that of the anomalous Hall
conductivity in ferromagnetic metals. Furthermore, each transition metal shows
huge and positive -orbital Hall conductivity (OHC), independently of the
strength of the spin-orbit interaction (SOI). Since the OHC is much larger than
the SHC, it will be possible to realize a {\it orbitronics device} made of
transition metals.Comment: 17 pages, 12 figures, 3 tables, resubmitted to Physical Review
Phase Diagram of the Electron-Doped Cuprate Superconductors
We investigate the phase diagram of the electron-doped systems in high-Tc
cuprates. We calculate the superconducting transition temperature Tc, the
antiferromagnetic transition temperature TN, the NMR relaxation rate 1/T1 with
the antiferromagnetic fluctuations in the fluctuation-exchange (FLEX)
approximation and with the superconducting fluctuations in the self-consistent
t-matrix approximation. Obtained phase diagram has common features as those in
the hole-doped systems, including the antiferromagnetic state, the
superconducting state and the spin gap phenomenon. Doping-dependences of TN, Tc
and Tsg (spin gap temperature) are, however, different with those in the
hole-doped systems. These differences are due to the intrinsic nature of the
ingap states which are intimately related with the Zhang-Rice singlets in the
hole-doped systems and are correlated d-electrons in the electron-doped
systems, respectively, which has been shown in the d-p model.Comment: 4 pages, 3 figure
Phase separation and valence instabilities in cuprate superconductors. Effective one-band model approach
We study the Cu-O valence instability (VI) and the related phase separation
(PS) driven by Cu-O nearest-neighbor repulsion , using an effective
extended one-band Hubbard model () obtained from the extended
three-bandHubbard model, through an appropriate low-energy reduction.
is solved by exact diagonalization of a square cluster with 10 unit cells and
also within a slave-boson mean-field theory. Its parameters depend on doping
for or on-site O repulsion . The results using both
techniques coincide in that there is neither VI nor PS for doping levels
if eV. The PS region begins for eV
at large doping and increases with increasing . The PS also
increases with increasing on-site Cu repulsion .Comment: 16 pages and 10 figures in postscript format, compressed with uufile
Anomalous Transport Phenomena in Fermi Liquids with Strong Magnetic Fluctuations
In many strongly correlated electron systems, remarkable violation of the
relaxation time approximation (RTA) is observed. The most famous example would
be high-Tc superconductors (HTSCs), and similar anomalous transport phenomena
have been observed in metals near their antiferromagnetic (AF) quantum critical
point (QCP). Here, we develop a transport theory involving resistivity and Hall
coefficient on the basis of the microscopic Fermi liquid theory, by considering
the current vertex correction (CVC). In nearly AF Fermi liquids, the CVC
accounts for the significant enhancements in the Hall coefficient,
magnetoresistance, thermoelectric power, and Nernst coefficient in nearly AF
metals. According to the numerical study, aspects of anomalous transport
phenomena in HTSC are explained in a unified way by considering the CVC,
without introducing any fitting parameters; this strongly supports the idea
that HTSCs are Fermi liquids with strong AF fluctuations. In addition, the
striking \omega-dependence of the AC Hall coefficient and the remarkable
effects of impurities on the transport coefficients in HTSCs appear to fit
naturally into the present theory. The present theory also explains very
similar anomalous transport phenomena occurring in CeCoIn5 and CeRhIn5, which
is a heavy-fermion system near the AF QCP, and in the organic superconductor
\kappa-(BEDT-TTF).Comment: 100 pages, Rep. Prog. Phys. 71, 026501 (2008
Iterated perturbation theory for the attractive Holstein and Hubbard models
A strictly truncated (weak-coupling) perturbation theory is applied to the
attractive Holstein and Hubbard models in infinite dimensions. These results
are qualified by comparison with essentially exact Monte Carlo results. The
second order iterated perturbation theory is shown to be quite accurate in
calculating transition temperatures for retarded interactions, but is not as
accurate for the self energy or the irreducible vertex functions themselves.
Iterated perturbation theory is carried out thru fourth order for the Hubbard
model. The self energy is quite accurately reproduced by the theory, but the
vertex functions are not. Anomalous behavior occurs near half filling because
the iterated perturbation theory is not a conserving approximation. (REPLACED
WITH UUENCODED FIGURES AT THE END. THE TEXT IS UNCHANGED)Comment: 27 pages, RevTex (figures appended at end
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