216 research outputs found
Thermodynamic potential of the Periodic Anderson Model with the X-boson method: Chain Approximation
The Periodic Anderson Model (PAM) in the limit has been studied
in a previous work employing the cumulant expansion with the hybridization as
perturbation (M. S. Figueira, M. E. Foglio and G. G. Martinez, Phys. Rev. B
\textbf{50}, 17933 (1994)). When the total number of electrons is
calculated as a function of the chemical potential in the ``Chain
Approximation'' (CHA), there are three values of the chemical potential
for each in a small interval of at low (M. S Figueira, M. E
Foglio, Physica A 208 (1994)). We have recently introduced the ``X-boson''
method, inspired in the slave boson technique of Coleman, that solves the
problem of non conservation of probability (completeness) in the CHA as well as
removing the spurious phase transitions that appear with the slave boson method
in the mean field approximation. In the present paper we show that the X-boson
method solves also the problem of the multiple roots of that
appear in the CHA.Comment: 13 pages, 6 figures e-mails: [email protected], [email protected],
[email protected]
X-boson cumulant approach to the periodic Anderson model
The Periodic Anderson Model (PAM) can be studied in the infinite U limit by
employing the Hubbard X operators to project out the unwanted states. We have
already studied this problem employing the cumulant expansion with the
hybridization as perturbation, but the probability conservation of the local
states (completeness) is not usually satisfied when partial expansions like the
Chain Approximation (CHA) are employed. Here we treat the problem by a
technique inspired in the mean field approximation of Coleman's slave-bosons
method, and we obtain a description that avoids the unwanted phase transition
that appears in the mean-field slave-boson method both when the chemical
potential is greater than the localized level Ef at low temperatures (T) and
for all parameters at intermediate T.Comment: Submited to Physical Review B 14 pages, 17 eps figures inserted in
the tex
Thermodynamic properties of the periodic Anderson model:X-boson treatment
We study the specific dependence of the periodic Anderson Model (PAM) in the
limit of employing the X-boson treatment in two fifferent regimes of
the PAM: the heavy fermion Kondo (HF-K) and the heavy fermion local magnetic
regime (HF-LMM). We obtain a multiple peak structure for the specific heat in
agreement with experimental results as well as the increase of the electronic
effective mass at low temperatures associated with the HF-K regime. The entropy
per site at low T tends to zero in the HF-K regime, corresponding to a singlet
ground state, and it tends to in the HF-LMM, corresponding to a
doublet ground state at each site. The linear coefficient
of the specific heat qualitatively agrees with the experimental results
obtained for differents materials in the two regimes considered here.Comment: 9 pages, 14 figure
X-boson Cumulant Approach To The Topological Kondo Insulators
In this work we present a generalization of our previous work of the X-boson approach to the periodic Anderson model (PAM), adequate to study a novel class of intermetallic 4f and 5f orbitals materials: the topological Kondo insulators, whose paradigmatic material is the compound SmB6. For simplicity, we consider a version of the PAM on a 2D square lattice, adequate to describe Ce-based compounds in two dimensions. The starting point of the model is the 4f - Ce ions orbitals, with J 5/2 multiplet, in the presence of spin-orbit coupling. Our technique works well for all of the parameters of the model and avoids the unwanted phase transitions of the slave boson mean field theory. We present a critical comparison of our results with those of the usual slave boson method, that has been intensively used to describe this class of materials. We also obtain a new valence first order transition which we attribute to the dependence of the hybridization.568DIB; DirecciĂłn de InvestigaciĂłn, Universidad Nacional de ColombiaColeman, P., (1984) Phys. Rev., 29 (6), p. 3035Dzero, M., Sun, K., Galitski, V., Coleman, P., (2010) Phys. Rev. Lett., 104 (10), p. 106408Dzero, M., Sun, K., Coleman, P., Galitski, V., (2012) Phys. Rev., 85 (4), p. 045130Alexandrov, V., Dzero, M., Coleman, P., (2013) Phys. Rev. Lett., 111 (22), p. 226403Tran, M.T., Takimoto, T., Kim, K.S., (2012) Phys. Rev., 85 (12), p. 125128Legner, M., Rueg, A., Sigrist, M., Phys. Rev., 89, p. 085110Werner, J., Assaad, F.F., (2013) Phys. Rev., 88 (3), p. 035113Franco, R., Figueira, M.S., Foglio, M.E., (2003) Phys. Rev., 66 (4), p. 045112Steglich, F., Geibel, C., Gloss, K., Olesch, G., Schank, C., Wassilew, C., Loidl, A., Stewart, G.F., (1994) J. Low Temperature Phys., 95 (1-2), p. 3Derr, J., Knebel, G., Lapertot, G., Salce, B., Measson, M.-A., Flouquet, J., (2006) J. Phys.: Condens. Matter, 18 (6), p. 2089Natoli, V.D., Cohen, H.M., Fornberg, B., (1996) J. Computacional Phys., 126 (1), p. 9
The periodic Anderson model from the atomic limit and FeSi
The exact Green's functions of the periodic Anderson model for
are formally expressed within the cumulant expansion in terms of an effective
cumulant. Here we resort to a calculation in which this quantity is
approximated by the value it takes for the exactly soluble atomic limit of the
same model. In the Kondo region a spectral density is obtained that shows near
the Fermi surface a structure with the properties of the Kondo peak.
Approximate expressions are obtained for the static conductivity
and magnetic susceptibility of the PAM, and they are employed to fit
the experimental values of FeSi, a compound that behaves like a Kondo insulator
with both quantities vanishing rapidly for . Assuming that the system
is in the intermediate valence region, it was possible to find good agreement
between theory and experiment for these two properties by employing the same
set of parameters. It is shown that in the present model the hybridization is
responsible for the relaxation mechanism of the conduction electrons.Comment: 26 pages and 8 figure
Fano resonance in electronic transport through a quantum wire with a side-coupled quantum dot: X-boson treatment
The transport through a quantum wire with a side coupled quantum dot is
studied. We use the X-boson treatment for the Anderson single impurity model in
the limit of . The conductance presents a minimum for values of T=0
in the crossover from mixed-valence to Kondo regime due to a destructive
interference between the ballistic channel associated with the quantum wire and
the quantum dot channel. We obtain the experimentally studied Fano behavior of
the resonance. The conductance as a function of temperature exhibits a
logarithmic and universal behavior, that agrees with recent experimental
results.Comment: 6 pages, 10 eps figs., revtex
Experimental study of a liquid Xenon PET prototype module
A detector using liquid Xenon in the scintillation mode is studied for
Positron Emission Tomography (PET). The specific design aims at taking full
advantage of the liquid Xenon properties. It does feature a promising
insensitive to any parallax effect. This work reports on the performances of
the first LXe prototype module, equipped with a position sensitive PMT
operating in the VUV range (178 nm).Comment: Proc. of the 7th International Workshops on Radiation Imaging
Detectors (IWORID-7), Grenoble, France 4-7 July 200
G Electronics and Data Acquisition (Forward-Angle Measurements)
The G parity-violation experiment at Jefferson Lab (Newport News, VA) is
designed to determine the contribution of strange/anti-strange quark pairs to
the intrinsic properties of the proton. In the forward-angle part of the
experiment, the asymmetry in the cross section was measured for
elastic scattering by counting the recoil protons corresponding to the two
beam-helicity states. Due to the high accuracy required on the asymmetry, the
G experiment was based on a custom experimental setup with its own
associated electronics and data acquisition (DAQ) system. Highly specialized
time-encoding electronics provided time-of-flight spectra for each detector for
each helicity state. More conventional electronics was used for monitoring
(mainly FastBus). The time-encoding electronics and the DAQ system have been
designed to handle events at a mean rate of 2 MHz per detector with low
deadtime and to minimize helicity-correlated systematic errors. In this paper,
we outline the general architecture and the main features of the electronics
and the DAQ system dedicated to G forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section
A. It has been written with Latex using \documentclass{elsart}. Nuclear
Instruments and Methods in Physics Research Section A: Accelerators,
Spectrometers, Detectors and Associated Equipment In Press (2007
Antimicrobial Potential Of Some Plant Extracts Against Candida Species.
The increase in the resistance to antimicrobial drugs in use has attracted the attention of the scientific community, and medicinal plants have been extensively studied as alternative agents for the prevention of infections. The Candida genus yeast can become an opportunistic pathogen causing disease in immunosuppressive hosts. The purpose of this study was to evaluate dichloromethane and methanol extracts from Mentha piperita, Rosmarinus officinalis, Arrabidaea chica, Tabebuia avellanedae, Punica granatum and Syzygium cumini against Candida species through the analysis of Minimum Inhibitory Concentration (MIC). Results presented activity of these extracts against Candida species, especially the methanol extract.701065-
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