Generalized Kondo Lattice Research Articles

Many-body localization in generalized Kondo lattice with disorder

We study the many-body localization transition in a one-dimensional generalized Kondo lattice, where a one-dimensional Hubbard chain with disordered spin-orbit coupling interacts with a fixed impurity of spin . Using exact diagonalization, we characterize the many-body localized transition with entanglement entropy and energy spectrum distribution. We find that although the subsystem of the impurity is free of disorder, it can still be localized in the spin space by the coupling with the Hubbard chain. We also investigate the out-of-time-order correlation in the many-body localized phase, and find distinctive features in comparison to either the thermal state or the Anderson localized state. Our scheme can be realized in experiments with ultracold fermions of alkaline-earth–like atoms near an orbital Feshbach resonance.

Generalized Kondo lattice model and its spin-polaron realization by the projection method for cuprates

The spin–fermion model, which is an effective low-energy realization of the three-band Emery model after passing to the Wannier representation for the px and py orbitals of the subsystem of oxygen ions, reduces to the generalized Kondo lattice model. A specific feature of this model is the existence of spin-correlated hoppings of the current carriers between distant cells. Numerical calculations of the spectrum of spin-electron excitations highlight the important role of the long-range spin-correlated hoppings.

Staggered Order with Itinerant and Localized Singlets in Generalized Kondo Lattice

The generalized Kondo lattice where even number of localized electrons are coupled with two conduction bands is investigated using the dynamical mean-field theory combined with continuous-time quantum Monte Carlo method. The crystalline electric field (CEF) singlet-triplet states are taken for localized states. With one conduction electron per site, a staggered order with Kondo and CEF singlets arises. Nature of the electronic order is studied in terms of the local susceptibility. The effective CEF splitting in one sublattice remains almost the same as the original CEF splitting, while the other sublattice looks like Kondo singlets. Hence, this electronic order is interpreted as alternating sites of itinerant and localized singlet states.

Spin-wave dispersion softening in the ferromagnetic Kondo lattice model for manganites

Spin dynamics is calculated in the ferromagnetic (FM) state of the generalized Kondo lattice model taking into account strong on-site correlations between e g electrons and antiferromagnetic (AFM) exchange among t 2 g spins. Our study suggests that competing FM double-exchange and AFM super-exchange interaction lead to a rather nontrivial spin-wave spectrum. While spin excitations have a conventional Dq 2 spectrum in the long-wavelength limit, there is a strong deviation from the spin-wave spectrum of the isotropic Heisenberg model close to the zone boundary. The relevance of our results to the experimental data are discussed.

Low-lying properties in a decorated Heisenberg spin chain

A decorated quantum spin chain is introduced, which realizes the strong coupling limit of a generalized Kondo lattice model at half-filling. The low-lying properties of the decorated spin system are discussed. In the continuum and semiclassical limit of the present model, the nonlinear sigma model with a topological term is derived and the conjecture for the low-lying state is proposed. Validity of the conjecture seems to be supported by the perturbational expansions and by the density matrix renormalization group calculations.

On the splitting of the lower band of charged elementary excitations of a two-dimensional antiferromagnet

A spin-polaron approach is developed on the basis of a generalized Kondo lattice model for a two-dimensional antiferromagnet (CuO2 plane model). This approach makes it possible to describe the splitting of polaron bands of carriers both in the presence of long-range magnetic order (T=0) and for a finite spin-correlation length (T≠0) and also can account for the strong deviation from the Luttinger theorem and the shadow-bands effect at both zero and finite temperatures.

Interplay between chains of localised spins and two-dimensional sheets of organic donors in the synthetically built magnetic multilayer

In order to understand the magnetic field-induced restoration of a highly conductive state in λ ‒ (BETS)2FeCl4, static (SQUID) and dynamic (ESR and AFR) magnetization measurements were performed on polycrystalline samples and single crystals, respectively. In addition, cantilever and resistivity measurements under steady fields were performed. While the metal-insulator transition curve of the (T, B) phase diagram exhibits a first order character, a “spin-flop” transition line divides the insulating state when the magnetic field is applied along the easy axis of magnetization. The effects of a RKKY-type indirect exchange and of applied magnetic field are described within the framework of a generalized Kondo lattice, namely two chains of S = 5/2 Fe3+ localised spins coupled through the itinerant spins of the 2D sheets of BETS. The calculations, which can incorporate intramolecular electron correlations within a mean field theory, are in qualitative agreement with the field induced transition from the antiferromagnetic insulating ground state to a canted one, i.e. a not fully oriented paramagnetic, but metallic state.

Magnetic Phase Diagram of a Generalized Kondo Lattice Model with Classical Localized Spins

We study the magnetic ground state of a generalized Kondo lattice model with classical localized spins, which includes antiferromagnetic exchange interaction J between localized spins. We determine the magnetic phase diagram on the plane of J and fermion concentration n , examining all possibilities of planar order of the localized spins in two dimensions. We find canted ferromagnetic phases, diagonal spiral phases, stripe spiral phases as well as the Neel ordered phase and the ordinary ferromagnetic phase. The densities of states of the fermions for these localized spin state are calculated. For small n , we analytically examined the stability of the Neel state and the ferromagnetic state in detail in any dimensions. We also discuss the t - J limit, J K / t →∞, for small n .

Spiral spin states in a generalized Kondo lattice model with classical localized spins

A generalized Kondo lattice model with classical localized spins is studied in a two-dimensional case. Our model includes the case in which antiferromagnetic exchange coupling J exists between localized spins. We obtain the magnetic phase diagram on the plane of J and fermion concentration n, and the order of each phase transition on the phase diagram, taking into account all possible planar spiral orders and canted ferromagnetic orders as well as the N\'eel order and the ordinary ferromagnetic order. In the phase diagram, we find a large region of the stripe spiral phase, which is consistent with the results of neutron-scattering experiments of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$.

Magnon Exchange Mechanism of Superconductivity in a Generalized Kondo Lattice Model

Magnon exchange mechanism of superconductivity is studied on the basis of the spin fermion model or a generalized Kondo lattice model, where the antiferromagnetic long range or short range order exists in the localized spins. We obtain the effective interaction and the gap equation taking into account the two magnon exchange interaction. The gap equation is solved just below the transition temperature in the quasi-two-dimensional cases. As a result, it is found that the triplet pairing superconductivity is favored for dilute fermion densities, while the singlet pairing is favored for high densities. The transition temperature is found to be very low for realistic parameters. The possibility that the superconductivity by the magnon exchange interaction is observed experimentally is discussed.

Fermion-Magnon Bound State in a Spin-Fermion Model

Spin-fermion model, or a generalized Kondo lattice model, in the phase where the localized spins are antiferromagnetically ordered, is studied. We obtain the bound state wave function of a single fermion and a single magnon with corrections of spin polaron analogous to the ordinary polaron, under some simplifying conditions analogous to Cooper's problem of the superconductivity. It is found that each fermion-magnon bound state extends over the whole space unlike the localized bound state in the single impurity Kondo model. It is also shown that there exists a finite critical value of the Kondo coupling for the bound state formation in the presense of the three dimensional interactions. We discuss the instability of the fermi surface.