877 research outputs found
Heavy fermion d-wave superconductivity: a X-boson approach
From an extension of the periodic Anderson model (PAM) in the
limit taking into account the effect of a nearest neighbor attractive
interaction between -electrons, we compare the obtained superconducting
phase diagram of a two dimensional d-wave superconductor with the results
obtained for an isotropic s-wave superconductor employing the X-boson method.Comment: Submitted to the Proceeding of the ICM 2003-Rome. Requires
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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 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; Dirección de Investigación, 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
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
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
Desarrollo de un proceso de salud eco amigable para el tratamiento de cicatrices patológicas excesivas
An eco-friendly health process has been designed and implemented for the treatment of excessive pathological scars such as keloids, hypertrophic and inesthetic scars through the use of photons from sunlight as a non-invasive, safe and effective alternative technique in contrast to technical techniques currently used that may be ineffective and risky, that use chemical inputs, energy from non-renewable sources (electrical) and that, often problems of prolonged treatment times. This eco-friendly process oriented to the topic of health is made up of three constitutive units: unit of analysis, treatment and cutaneous rehabilitation, which includes from the identification of the pathology and its own characteristics (thickness, size, pigmentation, etc.); until the prescription of the appropriate treatment and rehabilitation for the affected area. The process uses sunlight for treatment and improvements in the recovery of the affected tissue are expected, thus overcoming the functional limitations caused, it also relieves pain and the disappearance of edemas by 100% and up to 90% improvement in consistency, thickness and appearance of the skin. The process can be applied to patients of any age, sex and in any state of health.Un proceso de salud eco-amigable ha sido diseñado e implementado para el tratamiento de cicatrices patológicas excesivas como queloides, cicatrices hipertróficas e inestéticas mediante el uso de fotones provenientes de la luz solar como técnica alternativa no invasiva, inocua y efectiva en contraste a las técnicas convencionales actualmente empleadas que tienden a ser poco efectivas y riesgosas, que emplean insumos quÃmicos, energÃa de fuentes no renovables (eléctrica) y que, muchas veces requieren de tiempos prolongados en el tratamiento. Este proceso eco amigable orientado al tema de salud está conformado por tres unidades constitutivas: la unidad de análisis, de tratamiento y de rehabilitación cutánea, que abarca desde la identificación de la patologÃa y sus caracterÃsticas propias (grosor, tamaño, pigmentación, etc.); hasta la prescripción del tratamiento y rehabilitación adecuada para la zona afectada. El proceso utiliza luz solar para el tratamiento y se esperan mejoras en la recuperación del tejido afectado, superándose asà las limitaciones funcionales causadas, asà mismo alivia el dolor y la desaparición de edemas en un 100% y, hasta un 90% de mejorÃa en consistencia, grosor y aspecto de la piel. El proceso puede ser aplicado a pacientes de cualquier edad, sexo y en cualquier estado de salud
Reconciling inflation with openness
It is already understood that the increasing observational evidence for an
open Universe can be reconciled with inflation if our horizon is contained
inside one single huge bubble nucleated during the inflationary phase
transition. In this frame of ideas, we show here that the probability of living
in a bubble with the right (now the observations require ) can be comparable with unity, rather than infinitesimally small.
For this purpose we modify both quantitatively and qualitatively an intuitive
toy model based upon fourth order gravity. As this scheme can be implemented in
canonical General Relativity as well (although then the inflation driving
potential must be designed entirely ad hoc), inferring from the observations
that not only does not conflict with the inflationary paradigm,
but rather supports therein the occurrence of a primordial phase transition.Comment: 4 pages, one postscript figure, to be published on Physical Review D
PACS: 98.80. C
A new stump-toed frog from the transitional forests of NW Madagascar (Anura, Microhylidae, Cophylinae, Stumpffia)
Volume: 933Start Page: 139-16
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