We have investigated the valence transition in the extended periodic Anderson model (EPAM) within the framework of dynamical mean field theory. Previous theoretical studies have indicated the presence of this transition in parameter ranges that are experimentally inaccessible. In this work, we show that, inclusion of dynamics beyond static mean-field brings the valence transition in physically relevant regimes. We show the strong dependence of the quasiparticle-weight scale across the sharp valence crossover. The density of states also exhibit concomitant large scale spectral weight transfers, which can be observed in experiments.
We study valence fluctuation at finite temperatures in the periodic Anderson model with the Coulomb interaction between $f$ and conduction electons, combining dynamical mean-field theory with the non-crossing approximation. It is found that a large Coulomb repulsion induces a first-order valence transition. The finite temperature phase diagram is determined.
We study the extended Anderson model on the two-dimensional Penrose lattice, combining the real-space dynamical mean-field theory with the non-crossing approximation. It is found that the Coulomb repulsion between localized and conduction electrons does not induce a valence transition, but the crossover between the Kondo and mixed valence states in contrast to the conventional periodic system. In the mixed-valence region close to the crossover, nontrivial valence distributions appear characteristic of the Penrose lattice, demonstrating that the mixed-valence state coexists with local Kondo sta…
We study valence fluctuations in the extended Anderson model on two-dimensional Penrose lattice, using the real-space dynamical mean-field theory combined with the continuous-time Monte Carlo method. Calculating $f$-electron number, $c$-$f$ spin correlations, and magnetic susceptibility at each site, we find site-dependent formations of the singlet state and valence distribution at low temperatures, which are reflected by the quasiperiodic lattice structure. The bulk magnetic susceptibility is also addressed.
We study valence fluctuations at finite temperatures in the extended periodic Anderson model, where the Coulomb interaction between conduction and localized $f$-electrons is taken into account, using dynamical mean-field theory combined with the continuous-time quantum Monte Carlo (CT-QMC) method. The valence transition with the hysteresis is clearly found, indicating the first-order phase transition between the Kondo and mixed-valence states. We demonstrate that spin correlation rapidly develops when the system approaches the valence transition point. The comparison of the impurity solvers, %…
We investigate the behavior of the resistivity around valence transition in the one-dimensional extended periodic Anderson model (PAM) with the Coulomb repulsion between f and conduction electron U_fc. By using 1/N-expansion in the leading order in (1/N)^0, where N is the spin-orbital degeneracy of f-electrons, valence transition happens at critical U_fc with increasing the atomic f-level as seen in the previous work. We calculate the resistivity whole temperature range around valence transition based on the extended PAM including the crystal field and investigate how the physical properties s…
In this paper we have explored the role of valence fluctuations in an extended Anderson impurity model (e-SIAM) in which there is an additional Hubbard repulsion between conduction and impurity electrons, employing perturbative renormalization methods. We have calculated the scaling equations for the model parameters and solved them both analytically and numerically to find how valence fluctuations renormalize these parameters. Analytical solutions of the scaling equations yielded scaling invariants of the model which we find to be different than the Anderson impurity model signifying differen…
We present a neutron scattering investigation of Ce1-xYxAl3 as a function of chemical pressure, which induces a transition from heavy-fermion behavior in CeAl3 (TK=5 K) to a mixed-valence state at x=0.5 (TK=150 K). The crossover can be modeled accurately on an absolute intensity scale by an increase in the k-f hybridization, Vkf, within the Anderson impurity model. Surprisingly, the principal effect of the increasing Vkf is not to broaden the low-energy components of the dynamic magnetic susceptibility but to transfer spectral weight to high energy.
We present experimental results of electrical resistivity, Hall coefficient, magnetic susceptibility, and specific heat for single crystals of Ce-based intervalent compound CeNiSi$_2$. The results show similar behaviors observed in Yb-based intervalent compounds and support recent thoery of the Anderson lattice, in which the Fermi-liquid coherence is gloval over the whole lattice. There is a low-temperature scale $T_{coh} \sim$ 50 K for the onset of Fermi-liquid coherence, in addition to a high-temperature scale $T_K^* \sim$ 150 K for the Kondo-lattice condensation. Therefore, we conclude that…
Unconventional quantum criticality in heavy-fermion systems has been extensively analyzed in terms of a critical destruction of the Kondo effect. Motivated by a recent demonstration of quantum criticality in a mixed-valent heavy-fermion system, β-YbAlB4, we study a particle-hole-asymmetric Anderson impurity model with a pseudogapped density of states. We demonstrate Kondo destruction at a mixed-valent quantum critical point, where a collapsing Kondo energy scale is accompanied by a singular charge-fluctuation spectrum. Both spin and charge responses scale with energy over temperature (ω/T) and…
A very rich phase diagram has recently been found in CeCu$_{2}$Si$_{2}$ from high pressure experiments where, in particular, a transition between an intermediate valence configuration and an integral valent heavy fermion state has been observed. We show that such a valence transition can be understood in the framework of the periodic Anderson model. In particular, our results show a breakdown of a mixed-valence state which is accompanied by a drastic change in the \textit{f} occupation in agreement with experiment. This valence transition can possibly be interpreted as a collapse of the large …
We present the solution of the SU(N) x SU(M) Anderson impurity model using the Bethe-Ansatz. We first explain what extensions to the formalism were required for the solution. Subsequently we determine the ground state and derive the thermodynamics over the full range of temperature and fields. We identify the different regimes of valence fluctuation at high temperatures, followed by moment formation or intrinsic mixed valence at intermediate temperatures and a low temperature non-Fermi liquid phase. Among other things we obtain the impurity entropy, charge valence and specific heat over the fu…
We investigate the behavior of the periodic Anderson model in the presence of $d$-$f$ Coulomb interaction ($U_{df}$) using mean-field theory, variational calculation, and exact diagonalization of finite chains. The variational approach based on the Gutzwiller trial wave function gives a critical value of $U_{df}$ and two quantum critical points (QCPs), where the valence susceptibility diverges. We derive the critical exponent for the valence susceptibility and investigate how the position of the QCP depends on the other parameters of the Hamiltonian. For larger values of $U_{df}$, the Kondo re…
We solve the two-channel Anderson impurity model using the Bethe-Ansatz. We determine the ground state and derive the thermodynamics, obtaining the impurity entropy and specific heat over the full range of temperature. We show that the low temperature physics is given by a line of fixed points decribing a two-channel non Fermi liquid behavior in the integral valence regime associated with moment formation as well as in the mixed valence regime where no moment forms. We discuss relevance for the theory of UBe$_{13}$.
We present a general theory for the Fano resonance in Anderson impurity systems. It is shown that the broadening of the impurity level leads to an additional and important contribution to the Fano resonance around the Fermi surface, especially in the mixed valence regime. This contribution results from the interference between the Kondo resonance and the broadened impurity level. Being applied to the scanning tunnelling microscopic experiments, we find that our theory gives a consistent and quantitative account for the Fano resonance lineshapes for both Co and Ti impurities on Au or Ag surface…
It is shown that the Kondo lattice model, for any finite coupling constant J, can be obtained exactly from the periodic Anderson model in an appropriate limit. The mapping allows a direct proof of the 'large' Fermi volume for a nonmagnetic Fermi-liquid state of the Kondo lattice model.
An effective hamiltonian is derived exactly for the one-dimensional periodic Anderson model via a canonical transformation. The canonical transformation has been calculated up to infinite order, thus an exact transformation was performed in the strict mathematical sense. We also discuss briefly the impact of the obtained result on understanding the magnetic properties of several Kondo lattice compounds.
We present exact results for the periodic Anderson model for finite Hubbard interaction 0 <= U < +infinity on certain restricted domains of the model's phase diagram, in d=1 dimension. Decomposing the Hamiltonian into positive semidefinite terms we find two quantum states to be ground state, an insulating and a metallic one. The ground state energy and several ground state expectation values are calculated.
A one-parameter family of models that interpolates between the periodic Anderson model with infinite repulsion at half-filling and a model whose ground state is exactly the Resonating-Valence-Bond state is studied. It is shown numerically that the excitation gap does not collapse. Therefore the ground states of the two models are adiabatically connected.
The intermediate valence compounds Yb2M3Ga9 (M = Rh, Ir) exhibit an anisotropic magnetic susceptibility. We report measurements of the temperature dependence of the 4f occupation number, nf(T), for Yb2M3Ga9 as well as the magnetic inelastic neutron scattering spectrum Smag at 12 and 300 K for Yb2Rh3Ga9. Both nf(T) and Smag were calculated for the Anderson impurity model with crystal field terms within an approach based on the non-crossing approximation. These results corroborate the importance of crystal field effects in these materials; they also suggest that Anderson lattice effects are impo…
The valence level photoemission spectra in the Anderson impurity model for Ce compounds at zero temperature are studied as a function of the photon energy $ω$. Most of former studies on Ce compounds are based on the sudden approximation, which is valid in high energy region. For the photoemission in the adiabatic limit of low energy region, one should consider the dipole matrix elements and the hole-induced photoelectron scattering potential. We can manage it by combining the time-evolution formalism and the $1/N_f$ scheme in a large $f$-level degeneracy $N_f$. This gives the exact results as …
Using numerical renormalization group method the temperature dependences of the magnetic susceptibility $χ(T)$ and specific heat $C(T)$ are obtained in the single-impurity Anderson model with inclusion of the $d-f$ Coulomb interaction. It is shown that the exciton effects owing to this interaction can change considerably the dependence $C(T)$ in comparison with the standard Anderson model at not too low temperatures, whereas the dependence $χ(T)$ remains universal. The renormalization of the effective hybridization parameter and $f$-level position, which is connected with the $d-f$ interaction…
We solve the Periodic Anderson model in the Mott-Hubbard regime, using Dynamical Mean Field Theory. Upon electron doping of the Mott insulator, a metal-insulator transition occurs which is qualitatively similar to that of the single band Hubbard model, namely with a divergent effective mass and a first order character at finite temperatures. Surprisingly, upon hole doping, the metal-insulator transition is not first order and does not show a divergent mass. Thus, the transition scenario of the single band Hubbard model is not generic for the Periodic Anderson model, even in the Mott-Hubbard re…
The competition between the Ruderman-Kittel-Kasuya-Yosida effect and Kondo effect is a central subject of periodic Anderson model. By using the density matrix embedding theory, we study a three orbital periodic Anderson model, in which the effects of degenerate conduction orbitals via the local magnetic moments, number of electrons, and spin-spin correlation functions, are investigated. From the phase diagram at half filling, we find there exists two different anti-ferromagnetic phases and one paramagnetic phase. To explore the difference of the two anti-ferromagnetic phases, the topology of F…
We show analytically that, under certain assumptions, the periodic Anderson model and the Hubbard model become equivalent within the dynamical mean field theory for quasiparticle weight Z -> 0. A scaling relation is derived which is validated numerically using the numerical renormalization group at zero temperature and quantum Monte Carlo simulations at finite temperatures. Our results show that the f-electrons of the half-filled periodic Anderson model with nearest neighbor hybridization get localized at a finite critical interaction strength U_c}, also at zero temperature. This transition is…
The effect of binary alloy disorder on the ferromagnetic phases of f-electron materials is studied within the periodic Anderson model. We find that disorder in the conduction band can drastically enhance the Curie temperature due to an increase of the local f-moment. The effect may be explained qualitatively and even quantitatively by a simple theoretical ansatz. The emergence of an alloy Kondo insulator at non-integer filling is also pointed out.
The asymmetric infinite-dimensional periodic Anderson model is examined with a quantum Monte Carlo simulation. For small conduction band filling, we find a severe reduction in the Kondo scale, compared to the impurity value, as well as protracted spin screening consistent with some recent controversial photoemission experiments. The Kondo screening drives a ferromagnetic transition when the conduction band is quarter-filled and both the RKKY and superexchange favor antiferromagnetism. We also find RKKY-driven ferromagnetic and antiferromagnetic transitions.
We determine exactly the ground state of the one-dimensional periodic Anderson model (PAM) in the strong hybridization regime. In this regime, the low energy sector of the PAM maps into an effective Hamiltonian that has a ferromagnetic ground state for any electron density between half and three quarters filling. This rigorous result proves the existence of a new magnetic state that was excluded in the previous analysis of the mixed valence systems.
The magnetic and non-magnetic ground states of the periodic Anderson model with Coulomb interaction between $f$-electrons on the nearest-neighbour(NN) sites are investigated using a variational method, which gives exact calculation of the expectation values in the limit of infinite dimensions. It is shown that for a critical value of NN Coulomb interactions the magnetic ground state of the periodic Anderson model in the Kondo regime is unstable. Factors in terms of the physical processes responsible for instability of the magnetic ground state are also discussed. Our study indicates the import…
We present numerically exact predictions of the periodic and single-impurity Anderson models to address photoemission experiments on heavy Fermion systems. Unlike the single impurity model the lattice model is able to account for the enhanced intensity, dispersion, and apparent weak temperature dependence of the Kondo resonant peak seen in recent controversial photoemission experiments. We present a consistent interpretation of these results as a crossover from the impurity regime to an effective Hubbard model regime described by Nozieres.
The three dimensional periodic Anderson model is studied with Quantum Monte Carlo. We find that the cross-over to the Kondo singlet regime is remarkably sharp at low temperatures, and that the behavior of magnetic correlations is consistently reflected in both the thermodynamics and the density of states. The abruptness of the transition suggests that energy changes associated with the screening of local moments by conduction electrons might be sufficient to drive large volume changes in systems where applied pressure tunes the ratio of interband hybridization to correlation energy.
We investigate the effect of magnetic fields on a Kondo insulator by using the periodic Anderson model. The analysis by dynamical mean field theory combined with quantum Monte Carlo simulations reveals that the magnetic field drives the Kondo insulator to a transverse antiferromagnetic insulator at low temperatures. We calculate the staggered spin susceptibility and find its divergence signaling the antiferromagnetic instability. Further investigation of the spin correlation functions and the magnetization process clarifies how the magnetic field suppresses the Kondo singlet formation and indu…
We study the doping driven Mott metal-insulator transition (MIT) in the periodic Anderson model set in the Mott-Hubbard regime. A striking asymmetry for electron or hole driven transitions is found. The electron doped MIT at larger U is similar to the one found in the single band Hubbard model, with a first order character due to coexistence of solutions. The hole doped MIT, in contrast, is second order and can be described as the delocalization of Zhang-Rice singlets.
We study an extended periodic Anderson model with the Coulomb interaction Ucf between conduction and f electrons by the Gutzwiller method. The crossovers between the Kondo, intermediate-valence, and almost empty f-electron regimes become sharper with Ucf, and for a sufficiently large Ucf, become first-order phase transitions. In the Kondo regime, a large enhancement in the effective mass occurs as in the ordinary periodic Anderson model without Ucf. In addition, we find that a large mass enhancement also occurs in the intermediate-valence regime by the effect of Ucf.
Recently, dynamical mean field theory calculations have shown that kinks emerge in the real part of the self energy of strongly correlated metals close to the Fermi level. This gives rise to a similar behavior in the quasi-particle dispersion relation as well as in the electronic specific heat. Since f-electron systems are even more strongly correlated than the -hitherto studied- d-electron systems we apply the dynamical mean field approach with the numerical renormalization group method as impurity solver to study whether there are kinks in the periodic Anderson model.
We discuss the "exhaustion" problem in the context of the Periodic Anderson Model using Iterated Perturbation Theory(IPT) within the Dynamical Mean Field Theory. We find that, despite its limitations, IPT captures the exhaustion physics, which manifests itself as a dramatic, strongly energy dependent suppression of the effective Anderson impurity problem. As a consequence, low energy scales in the lattice case are strongly suppressed compared to the "Kondo scale" in the single-impurity picture. The IPT results are in qualitative agreement with recent Quantum Monte Carlo results for the same pr…
We investigate the competition of the Kondo and the RKKY interactions in heavy fermion systems. We solve a periodic Anderson model using Extended Dynamical Mean Field Theory (EDMFT) with QMC. We monitor simultaneously the evolution of the electronic and magnetic properties. As the RKKY coupling increases the heavy fermion quasiparticle unbinds and a local moment forms. At a critical RKKY coupling there is an onset of magnetic order. Within EDMFT the two transitions occur at different points and the disapparence of the magnetism is not described by a local quantum critical point.
We present a class of exact ground states of a three-dimensional periodic Anderson model at 3/4 filling. Hopping and hybridization of d and f electrons extend over the unit cell of a general Bravais lattice. Employing novel composite operators combined with 55 matching conditions the Hamiltonian is cast into positive semidefinite form. A product wave function in position space allows one to identify stability regions of an insulating and a conducting ground state. The metallic phase is a non-Fermi liquid with one dispersing and one flat band.
The ferromagnetic phase diagram of the periodic Anderson model is calculated using dynamical mean-field theory in combination with the modified perturbation theory. Concentrating on the intermediate valence regime, the phase boundaries are established as function of the total electron density, the position of the atomic level and the hybridization strength. The main contribution to the magnetic moment stems from the f-electrons. The conduction band polarization is, depending on the system parameters either parallel or antiparallel to the f-magnetization. By investigating the densities of state…
We study ground state properties of periodic Anderson model in a two-dimensional square lattice with variational Monte Carlo method. It is shown that there are two different types of quantum phase transition: a conventional antiferromagnetic transition and a Fermi-surface reconstruction which accompanies a change of topology of the Fermi surface. The former is induced by a simple back-folding of the Fermi surface while the latter is induced by localization of $f$ electrons. The mechanism of these transitions and the relation to the recent experiments on Fermi surface are discussed in detail.
Recent experiments have suggested that the electron-phonon coupling may play an important role in the $γ\rightarrow α$ volume collapse transition in Cerium. A minimal model for the description of such transition is the periodic Anderson model. In order to better understand the effect of the electron-phonon interaction on the volume collapse transition, we study the periodic Anderson model with coupling between Holstein phonons and electrons in the conduction band. We find that the electron-phonon coupling enhances the volume collapse, which is consistent with experiments in Cerium. While we st…
We study the phase diagram and quantum critical region of one of the fundamental models for electronic correlations: the periodic Anderson model. Employing the recently developed dynamical vertex approximation, we find a phase transition between a zero-temperature antiferromagnetic insulator and a Kondo insulator. In the quantum critical region, we determine a critical exponent $γ\!=\!2$ for the antiferromagnetic susceptibility. At higher temperatures, we have free spins with $γ\!=\!1$ instead, whereas at lower temperatures, there is an even stronger increase and suppression of the susceptibil…
Diagrammatic theory for Periodic Anderson Model has been developed, supposing the Coulomb repulsion of $f-$ localized electrons as a main parameter of the theory. $f-$ electrons are strongly correlated and $c-$ conduction electrons are uncorrelated. Correlation function for $f-$ and mass operator for $c-$ electrons are determined. The Dyson equation for $c-$ and Dyson-type equation for $f-$ electrons are formulated for their propagators. The skeleton diagrams are defined for correlation function and thermodynamic functional. The stationary property of renormalized thermodynamic potential about…
We study magnetic properties of the extended periodic Anderson model, which includes electron correlations within and between itinerant and localized bands. By combining dynamical mean-field theory with the numerical renormalization group we calculate the sublattice magnetization and the staggered susceptibility to determine the phase diagram in the particle-hole symmetric case. We find that two kinds of magnetically ordered states compete with the Kondo insulating state at zero temperature, which induces non-monotonic behavior in the temperature-dependent magnetization. It is furthermore clar…
We investigate quantum phase transitions in the extended periodic Anderson model, which includes electron correlations within and between itinerant and localized bands. We calculate zero and finite temperature properties of the system using the combination of dynamical mean-field theory and the numerical renormalization group. At half filling, a phase transition between a Mott insulating state and a Kondo insulating state occurs in the strong coupling regime. We furthermore find that a metallic state is stabilized in the weak coupling regime. This state should be adiabatically connected to the…
We demonstrate that the conductance through a single-electron transistor at low temperature is in quantitative agreement with predictions of the equilibrium Anderson model. When an unpaired electron is localized within the transistor, the Kondo effect is observed. Tuning the unpaired electron's energy toward the Fermi level in nearby leads produces a cross-over between the Kondo and mixed-valence regimes of the Anderson model.
We study the momentum distribution of the electrons in an extended periodic Anderson model, where the interaction, $U_{cf}$, between itinerant and localized electrons is taken into account. In the symmetric half-filled model, due to the increase of the interorbital interaction, the $f$ electrons become more and more delocalized, while the itinerancy of conduction electrons decreases. Above a certain value of $U_{cf}$ the $f$ electrons become again localized together with the conduction electrons. In the less than half-filled case, we observe that $U_{cf}$ causes strong correlations between the…
We study the symmetric periodic Anderson model of the conduction electrons hybridized with the localized correlated electrons on square lattice. Using the canonical representation of electrons by Kumar, we do a self-consistent theory of its effective charge and spin dynamics, which produces an insulating ground state that undergoes continuous transition from the Kondo singlet to Néel antiferromagnetic phase with decreasing hybridization, and uncovers two inversion transitions for the charge quasiparticles. With suitably inverted quasiparticle bands for moderate to weaker effective Kondo coupli…
This paper reports dynamical mean field calculations for the periodic Anderson model in which the conduction band is coupled to phonons. Motivated in part by recent attention to the role of phonons in the $γ$-$α$ transition in Ce, this model yields a rich and unexpected phase diagram which is of intrinsic interest. Specifically, above a critical value of the electron-phonon interaction, a first order transition with two coexisting phases develops in the temperature-hybridization plane, which terminates at a second order critical point. The coexisting phases display the familiar Kondo screened …
The single band Hubbard and the two band Periodic Anderson Hamiltonians have traditionally been applied to rather different physical problems - the Mott transition and itinerant magnetism, and Kondo singlet formation and scattering off localized magnetic states, respectively. In this paper, we compare the magnetic and charge correlations, and spectral functions, of the two systems. We show quantitatively that they exhibit remarkably similar behavior, including a nearly identical topology of the finite temperature phase diagrams at half-filling. We address potential implications of this for the…
Monte Carlo-maximum entropy calculations of the conductivity of the infinite-dimensional periodic Anderson model are presented. We show that the optical conductivity displays anomalies associated with the exhaustion of conduction-band states near the Fermi energy including a Drude weight which rises with temperature, with weight transferred from a temperature and doping-dependent mid-IR peak and a low-frequency incoherent contribution. Both the Drude and mid-IR peaks persist up to very high temperatures. The resistivity displays a non-universal peak and two other regions associated with impuri…
We investigate the paramagnetic periodic Anderson model using the dynamical mean-field theory in combination with the modified perturbation theory which interpolates between the weak and strong coupling limits. For the symmetric PAM, the ground state is always a singlet state. However, as function of the hybridization strength, a crossover from collective to local Kondo screening is found. Reducing the number of conduction electrons, the local Kondo singlets remain stable. The unpaired f-electrons dominate the physics of the system. For very low conduction electron densities, a large increase …
We study the Mott metal-insulator transition in the Periodic Anderson Model within Dynamical Mean Field Theory (DMFT). Near the quantum transition, we find a non-Fermi liquid metallic state down to a vanishing temperature scale. We identify the origin of the non-Fermi liquid behavior as due to magnetic scattering of the doped carriers by the localized moments. The non-Fermi liquid state can be tuned by either doping or external magnetic field. Our results show that the coupling to spatial magnetic fluctuations (absent in DMFT) is not a prerequisite to realize a non-Fermi liquid scenario for he…
The variational cluster approach (VCA) based on the self-energy functional theory is applied to the two-dimensional symmetric periodic Anderson model at half filling. We calculate a variety of physical quantities including the staggered moments and single-particle spectra at zero temperature to show that the symmetry breaking due to antiferromagnetic ordering occurs in the strong coupling region, whereas in the weak coupling region, the Kondo insulating state without symmetry breaking is realized. The critical interaction strength is estimated. We thus demonstrate that the phase transition due…
We introduce a new approach to the periodic Anderson model (PAM) that allows a detailed investigation of the magnetic properties in the Kondo as well as the intermediate valence regime. Our method is based on an exact mapping of the PAM onto an effective medium strong-coupling Hubbard model. For the latter, the so-called spectral density approach (SDA) is rather well motivated since it is based on exact results in the strong coupling limit. Besides the T=0 phase diagram, magnetization curves and Curie temperatures are presented and discussed with help of temperature-dependent quasiparticle den…
Using a two-channel Anderson model, we develop a theory of composite pairing in the 115 family of heavy fermion superconductors that incorporates the effects of f-electron valence fluctuations. Our calculations introduce "symplectic Hubbard operators": an extension of the slave boson Hubbard operators that preserves both spin rotation and time-reversal symmetry in a large N expansion, permitting a unified treatment of anisotropic singlet pairing and valence fluctuations. We find that the development of composite pairing in the presence of valence fluctuations manifests itself as a phase-cohere…
The Periodic Anderson Model (PAM) is widely studied to understand strong correlation physics and especially the competition of antiferromagnetism and singlet formation. Quantum Monte Carlo (QMC) studies have focused both on issues such as the nature of screening and locating the quantum critical point (QCP) at zero temperature and also on possible experimental connections to phenomena ranging from the Cerium volume collapse to the relation of the magnetic susceptibility and Knight shift in heavy fermions. In this paper we extend QMC work to lattices in which the conduction electron sites can h…
We compare different approximation schemes for investigating ferromagnetism in the periodic Anderson model. The use of several approximations allows for a detailed analysis of the implications of the respective methods, and also of the mechanisms driving the ferromagnetic transition. For the Kondo limit, our results confirm a previously proposed mechanism leading to ferromagnetic order, namely an RKKY exchange mediated via the formation of Kondo screening clouds in the conduction band. The contrary case is found in the intermediate-valence regime. Here, the bandshift correction ensuring a corr…
We study the temperature dependence of the specific heat in the periodic Anderson model as function of the on-site Coulomb interaction, hybridization, and position of the f-electrons energy level. At strong coupling (U=infinity) we use slave bosons, whereas at weak coupling we use a simple Hartree-Fock decomposition. We find that both in the strong and weak coupling limits the specific heat of the system presents a multiple peak structure in a mean field treatment. We believe these features to be related to band-shape effects. The temperature evolution of the low-temperature peak position on t…
We investigate the effect of hole and electron doping to half-filling in the periodic Anderson model on a triangular lattice by the Hartree-Fock approximation at zero temperature. At half-filling, the system exhibits a partially disordered insulating state, in which a collinear antiferromagnetic order on an unfrustrated honeycomb subnetwork coexists with nonmagnetic state at the remaining sites. We find that the carrier doping destabilizes the partially disordered state, resulting in a phase separation to a doped metallic state with different magnetic order. The partially disordered state is r…
