M. E. Foglio

Thermodynamic potential of the periodic Anderson model with the X-boson method: chain approximation

The periodic Anderson model (PAM) in the U→∞ limit has been studied in a previous work employing the cumulant expansion with the hybridization as perturbation (Figueira et al., Phys. Rev. B 50 (1994) 17933). When the total number of electrons Nt is calculated as a function of the chemical potential μ in the “chain approximation” (CHA), there are three values of the chemical potential μ for each Nt in a small interval of Nt at low T (Physica A 208 (1994) 279). We have recently introduced the “X-boson” method, inspired in the slave boson technique of Coleman, that solves the problem of nonconservation 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 Nt(μ) that appear in the CHA.

X-slave boson approach to the periodic Anderson model

Abstract The periodic anderson model (PAM) in the limit U=∞, can be studied by employing the Hubbard X operators to project out the unwanted states. In a previous work, we have studied the cumulant expansion of this Hamiltonian employing the hybridization as a perturbation, but probability conservation of the local states (completeness) is not usually satisfied when partial expansions like the “chain approximation (CHA)” are employed. To consider this problem, we use a technique similar to the one employed by Coleman to treat the same problem with slave-bosons in the mean-field approximation. Assuming a particular renormalization for hybridization, we obtain a description that avoids an unwanted phase transition that appears in the mean-field slave-boson method at intermediate temperatures.

Thermodynamic properties of the periodic Anderson model: X-boson treatment

We study the specific-heat dependence of the periodic Anderson model (PAM) in the limit of

Periodic Anderson model from the atomic limit and FeSi

U=\ensuremath{\infty}

Intermediate valence of the hyperfine field of cerium in gadolinium metal

employing the X-boson treatment in two different regimes of the PAM: the heavy fermion Kondo (HF-K) and the local magnetic moment regime (HF-LMM). We obtain a multiple peak structure for the specific heat in agreement with the 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

X-boson cumulant approach to the topological Kondo insulators

{k}_{B}\mathrm{ln}2

Periodic Anderson model from the atomic limit : magnetic and transport properties of FeSi

in the HF-LMM, corresponding to a doublet ground state at each site. The linear coefficient

Perturbative Results Using the Cumulant Expansion in the Anderson Lattice

\ensuremath{\gamma}{(T)=C}_{v}(T)/T

Relaxation rate of an intermediate valence Eu impurity

of the specific heat qualitatively agrees with the experimental results obtained for different materials in the two regimes considered here.

The relaxation rate of europium in europium iron garnet

The exact Greens functions of the periodic Anderson model (PAM) for