Ground state of ferromagnet with antiferromagnetic impurity

The Heisenberg ferromagnet with an antiferromagnetic impurity and arbitrary spin is considered. The method is suggested for constructing the ground state of such a system, the method using the Jacobi matrix technique. As an example, there has been investigated the ferromagnet with a simple cubic lattice and the matrix spin $\text{S =}\text{1}\text{2}$, and the impurity spin S′ = 1. The energy and wave function of the ground state are found as dependent on the system parameters.     

Ground state of an impurity in a homogeneous system in the hypernetted chain approximation

The hypernetted chain theory of the ground state of a homogeneous N-particle medium NM with an impurity particle is presented. The N identical particles are fermions with spin-isospin degeneracy ν, or bosons (in the limit of ν → ∞). The ground-state wave-function of the system is assumed in the Jastrow form with central, state-independent correlation functions. Central, spin-isospin-dependent two-body interactions both in NM and between the impurity particle and the particles of NM are considered. Expressions for the ground-state energy of the system and for the separation energy of the impurity particle are derived. The simplified case of the chain approximation is also considered.     

Ground state properties of the two impurity Anderson model in a 1/N expansion

The intersite contribution to the ground state energy for the two impurity Anderson model is calculated to first order in 1/N. The dependence of this contribution on the interimpurity separation has an R^?1 or R^?3 envelope for distances smaller or larger than a length ν_F/T_A ranges from a value equal to the bare ?-level position (in the weak valent regime) to the Kondo temperature (in the local moment limit).     

Ground state of magnetic dimers on metal surfaces

We present model studies of the ground state for magnetic dimers on metal surfaces. We find it can be neither ferromagnetic nor antiferromagnetic, but is often canted for nearest neighbors. Thus, the system cannot be described using bilinear exchange. We give a criterion which can be used quite generally to interrogate the local stability of ferromagnetically or antiferromagnetically aligned dimers, and which also may be used to infer the canting angle when canted states are stable.     

Properties of a magnetic impurity in a metal

The effect of a polarized conduction-electron cloud back on a magnetic impurity dissolved in a metal is studied. It is shown that at a temperature T _c much higher than the Kondo temperature the system becomes unstable against symmetry breaking and that a state with 〈S _z 〉 ≠ 0 is established. The behavior of 〈 S _z 〉 is derived for all temperatures and magnetic fields except for a very narrow region around T _c and for very low temperatures. The minute role of Kondo-type processes in establishing the symmetry-broken state is pointed out. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 184–189 (10 August 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Theory of an impurity state in a crystal

A review is given of the theory of the effects of single-, or low-concentration impurities on the properties of otherwise perfect crystals. The subjects considered include electron density, anomalies in the temperature dependence of the spontaneous magnetization of a ferromagnetic insulator and the spectrum of lattice vibrations. All the problems are considered from a single mathematical point of view in which the approximation of localized perturbations and Green function techniques are used. The conditions for the occurrence of localized and virtual states are discussed. The review concludes with a formulation of the general methods of the theory.     

Ground state energy of an exciton bound to an ionized donor impurity in semiconductor quantum wells

The ground state energy of an exciton bound to an ionized hydrogenic donor impurity placed at the centre of a semiconductor quantum well with finite barriers is calculated variationally as a function of the well width and the effective mass ratio of the electron and the hole within the envelope function approximation. For the GaAs/Ga_1-x Al_x As system with X = 0.15 and X = 0.30 the energy is minimum for a well width near 50 Angströms. This minimum is comprized between the values obtained in the 2D limits.     

The Polaron Self-Energy in a Parabolic Quantum Dot

Polaronic states in a parabolic quantum dot are investigated by using the second order Rayleigh-Schrödinger perturbation theory. It is shown that the absolute values of the ground state energy correction and the excited state energy correction as well as the relevant transition energies increase with decreasing the size of the quant um dot. The results also indicate that the polaron effects in small quantum dots are stronger than those in the corresponding bulk materials.     

Ground state of a dipolar crystal

We provide some of the strongest evidence to date that the ground state structure of an infinite collection of point dipoles with hardcore sphere interactions is body-centered tetragonal. The structure with the next highest binding energy is not face-centered cubic; a particular honeycomb structure has lower energy.     

Ground state energy of a polaron in a superlattice

The ground state energy of a polaron in a superlattice was calculated using the double-time Green functions. The effective mass of the polaron along the planes perpendicular to the superlattice axis was also calculated. The dependence of the ground state energy and the effective mass along the planes perpendicular to the superlattice axis on the electron–phonon coupling constant α and on the superlattice parameters (i.e. the superlattice periodd and the bandwidth Δ) were studied. It was observed that if an infinite square-well potential is assumed, the ground state energy of the polaron decreases (i.e. becomes more negative) with increasing α and d, but increases with increasing Δ. For small values of α, the polaron ground state energy varies slowly with Δ, becoming approximately constant for large Δ. The effective mass along the planes perpendicular to the superlattice axis was found to be approximately equal to the mass of an electron for all typical values ofα , d and Δ.     

Stark-shift of impurity fundamental state in a lens shaped quantum dot

We calculate the Stark effect and the polarisability of shallow-donor impurity located in the centre of lens shaped quantum dot by a variational method and in the effective-mass approximation. Our theoretical model assumes an infinite confinement to describe the barriers at the dot boundaries and the electric field is considered to be applied in the z-direction. The systematic theoretical investigation contains results with the quantum dot size and the strength of the external field. Our calculations reveal that the interval wherein the polarisability varies depends strongly on the dot size.     

Ground state in FeS

From a Mössbauer study of oriented single crystals of Fe_0.996S and Fe_0.93S at 615 K (above the Néel transition $\text{T}{}_{\mathrm{N}}\text{\$}\text{?}\text{598}\text{K}$) the sign of the quadrupole splitting is determined to be negative thereby indicating the ground state is ${}^5\text{A}{}_1$.     

Theory of quasimagnetic impurity in a metal: An exactly soluble model of interacting electrons

We study an impurity atom, on which two-body forces are important, dissolved in a metal, where they are negligible. With the aid of the well-known boson excitation spectrum of the electronic Fermi sea, we predict the low-energy effects of one- and two-body potentials on the impurity, in the nonmagnetic regime. We obtain for the first time exact expressions for the cutoff independent contributions to the specific heat and paramagnetic susceptibility, the spectral amplitudes or one-electron density of states on the impurity, and the scattering cross-section. The entire spectrum of manybody eigenstates is explicitly obtained. The onset of a local magnetic moment appears as a sudden breakdown of the model Hamiltonian, and occurs when the two-body potential exceeds a critical value U_c which is O(E_F) in magnitude. A study of the renormalization of the interaction parameters terminates the paper.     

一维铁磁/有机系统的基态与自旋分布研究

文中用一维紧束缚模型描述铁磁金属,用一维非简并的Su-Schrieffer -Heeger (SSH)模型描述共轭聚合物,研究了在一维铁磁/共轭聚合物系统和一维CMR材料/ 聚合物系统中的电子转移和自旋转移.发现在聚合物部分没有自旋的双极化子比有自旋的极化子具有较低的能量而容易产生.然而在铁磁CMR材料/聚合物系统中极化子的产生能低于聚合物中极化子的产生能,增加了有机物中自旋极化输运的可能性.     

Study of impurity behaviour in non-coronal equilibrium state

A physical model of analysing the behaviour of impurities out of coronal equilibrium in tokamak plasmas has been proposed. Through solving the time-dependent rate equations including the effects of atomic processes and the particle transport losses, the ionization state distribution is obtained for a range of low Z impurities such as helium, carbon, oxygen and argon. By using the ionization state distribution of these impurities, the radiation rate coefficients and the mean charge state changing with plasma temperature are calculated. The results show that the mean charge state （Z） is sensitively dependent on the parameter neT, and this is the reason why the radiation power of impurities under non-coronal equilibrium conditions is several orders of magnitude higher than that under coronal equilibrium condition.[第一段]     

Effects of intercrystallite impurity adsorption on the brittleness of a metal in a liquid

Results are given on the effects of intercrystallite adsorption of impurities in the solid metal on the brittleness in contact with liquid metals. The results can be used to develop methods of protection by microalloying of the solid metal, and they can be used with other evidence to check some existing ideas on the atomic mechanism of liquid-metal embrittlement.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 7–13, July, 1973.We are indebted to V. M. Demin for assistance in the experiments with A1 alloys.     

On the ground state of an impurity in a dilute fermi gas

The system under consideration is a large collection of identical fermions (B), forming a background, into which is inserted a relatively small number of distinct impurity (I) particles. The background is considered to be dilute in the sense that R ? a, where R is the average separation of the B particles, and a is the range of their interaction potential; and the I particles are so dilute with respect to the B particles that I-I interactions can be ignored. The I particles are then all essentially at rest in their ground state. The BB and BI interaction potentials are chosen to be hard cores of the same range a. A series expansion is developed for the ground-state energy of the I particles, and the first four terms are calculated explicitly using two distinct methods, employing Feynman and Goldstone diagrams respectively. It is shown that each method has distinct advantages over the other, and that a judicious combination of both can be used to considerable benefit.     

Ground state of a mixture of resonant condensates

It is shown that a two-component mixture of resonant condensates can be unstable toward the transition to the state with spontaneous Josephson oscillations in the absolute minimum of thermodynamic potential. The transition occurs stepwise at a certain critical value of the total number of particles or chemical potential.