Bethe-ansatz solution of the groundstate of a model for mixed-valent Ce and Yb impurities in metals

We consider an impurity model consistent of the 4f ⁰-singlet and a multiplet of total angular momentumj of the 4f ¹ configuration hybridized with conduction states of the metal. The model is solved by Bethe-ansatz and related to theU limit of the Anderson model. If thef-level is far below the Fermi level the equations are reduced to the Bethe-ansatz solution of the Coqblin-Schrieffer model. Approximate analytical results valid in the mixed valence regime are given. A numerical solution for the impurity groundstate energy,f-level occupancy and charge susceptibility as a function of thef-level energy and in the absence of a magnetic field is presented.On a Heisenberg fellowship of the Deutsche Forschungsgemeinschaft     

Magnetic-nonmagnetic transitions in intermediate-valence systems

We investigate the coexistence of ferromagnetism and intermediate valence in 4f-systems, which have ferromagnetic ground states in the normal valence phase and fluctuate between a magnetic (J0) and a nonmagnetic (J=0) configuration in the intermediate valence phase. We use the well-knowns-f model, which is extended by a hybridization term and an intraatomicf-Coulomb-interaction, for systems with ferromagnetics-f exchange. The alloy analogy of this model is solved within a CPA-scheme. We inspect the stability of the localf-momentm _f , the valencen _f and relevant quasiparticle densities of states in terms of the Bloch bandwidthW (closely related to external pressure!), thef-level positionE _f (alloying!), and the hybridization matrix elementV.     

Bethe-Ansatz solution of a model for a mixed valent impurity with two magnetic configurations: Groundstate and thermodynamics

We consider a mixed valence impurity with two magnetic configurations of spinJ ₂ andJ ₁=J ₂±1/2, respectively, coupled bys-wave conduction electrons via a hybridization matrix element. The model contains theU limit of the non-degenerate Anderson model and the Kondo exchange Hamiltonian for arbitrary spin as special cases. The model is solved by Bethe's ansatz and the groundstate and the thermodynamic properties are discussed. The Kondo limit and the highT perturbation expansion are extracted from the thermodynamic Bethe-ansatz equations. The ground state is magnetic if neitherJ ₁ norJ ₂ is a singlet.Heisenberg fellow of the Deutsche Forschungsgemeinschaft     

Bethe-ansatz solution of the groundstate of a model for mixed-valent Ce and Yb impurities in metals

We consider a model for Ce(Yb)-impurities consistent of the 4f⁰-singlet and a multiplet of total angular mometum j of the 4f¹-configuration hybridized with conduction states of the metal (U limit of Anderson's model). The Bethe-ansatz equations are solved analytically for the groundstate in the absence of an external magnetic field and exact expressions for the valence, spin and charge susceptibilities and the resistivity are given.     

Angular correlation for nuclear muon capture

Formulae for the capture rates, gamma-neutrino correlations, and angular distributions of recoil in muon capture processes J_i J_f by an unpolarized nucleus for J_i ≦ 3 and J_f ≦ 5/2, with and without change of parity of nuclear levels, are given explicitely in terms of the multipole amplitudes. Relation of helicity amplitudes for muonic atom decay to the multipole amplitudes and to amplitudes introduced by other authors is presented. The derivation is based on kinematics only, and the formulae are strictly valid for the muon capture by any nuclei. The formulae are convenient for model calculations of partial transitions with realistic nuclear and muon wave functions and for the phenomenological analysis of a weak interaction.     

Antiferromagnetism in 4f-systems with valence instabilities

An extendeds–f model is used for the study of intermediate-valence 4f-systems, which have antiferromagnetic ground states in the normal-valence phase and fluctuate between a magnetic and a nonmagnetic configuration in the intermediate-valence phase. The local magnetic 4f-moment, the sublattice-magnetization as well as the Néel-temperatureT _N are discussed in terms of thes–f hybridizationV and thef-level positionE _f . Reduction of the energy gap betweenE _f and conduction band simulates the influence of external pressure or of alloying with suitable impurities. IncreasingV or decreasing4f-(5d, 6s)-gap intensifies the electronic fluctuations, which have two competitive consequences. They tend to quench the local moments, but simultaneously enhance the coupling between them. This results in a typical behaviour of the Néel-temperature. Conditions for the coexistence of antiferro-magnetism and intermediate valence are derived. Comparison with experimental data for systems like Eu-metal and Eu(Pd_1–x Au _x )₂Si₂ shows qualitative agreement.     

Nuclear fusion rates from resonant states of 3Hedμ molecular ion

We present new theoretical calculations of nuclear fusion rates λ _f ^J from the resonant states of the muonic molecular ion ³Hedμ ⁺⁺ with total angular momenta J=0,1. As a byproduct, new very accurate variational wave functions for these states have been obtained. Using these wave functions, the probability density |Ψ(R=0)|² in a fusion region has been calculated by extrapolating the variational solution to small internuclear distances by means of the multi-channel adiabatic solution. Calculated fusion rates for the states J=0 and J=1 are: λ _f ⁰ =1.9·10⁵s^-1 and λ _f ¹ =0.65·10³s^-1, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rectification of the dipole force in a monochromatic field created by elliptically polarized waves

The rectification of the force of induced light pressure in laser fields formed by elliptically polarized running waves in zero magnetic field is considered. Explicit analytic expressions for the induced and spontaneous forces of light pressure exerted on a stationary atom are obtained for two classes of closed optical transitions: J _g=J→J _e=J+1 and J _g=J→J _e=J (J is half-integral), where J _g and J _e are the total angular momenta of the ground and excited energy levels. It is shown that the ellipticity of waves is the necessary condition for the emergence of the rectification of the induced force in a monochromatic field. The optimal parameters of the field and the maximum rectification coefficient are calculated for a number of optical transitions. The dependence of the rectified force on the velocity is investigated analytically and numerically for the simplest 1/2→1/2 transition.     

An application of a representation theorem for entropy functionals

The vibrational predissociation of HD₂ ⁺ is modelled in terms of quantum-mechanical tunnelling through a minimal centrifugal barrier at given total angular momentum, J, and with statistical intermode coupling behind the barrier. It is shown that the observed strong preference for the H⁺ + D ₂ predissociation channel (over D⁺ + HD) is consistent with an experimental preference for J values in the range 0 < J < 25, a range which is also shown to be consistent with the observed H₃ ⁺ preferred range of kinetic energy release. A correlation between the total angular momentum and the kinetic energy release is also predicted.     

Energy level scheme and the effect of magnetic order on the optical transitions in europium chalcogenides

The optical constants of Eu-chalcogenide single crystals have been determined at room temperature for photon energies from 1 to 6 eV. In the same energy range the transmission of thin evaporated films (except for EuO) has been measured with polarized light above and below the magnetic ordering temperature. The observed polarization-dependent splittings of the two main absorption maxima in the region of magnetic order suggest transitions from the 4f⁷-level into the crystal field split 5dt_2g- and 5de_g-states. An attempt has been made to relate the maxima of the absorption coefficient to interband transitions and transitions from the localized 4f-states. With this assumption we derived a consistent energy level scheme of the four Eu-chalcogenides. From the scheme we gained useful information about the width of the 5d-states, the crystal field splitting and the possible type of conductivity. Finally we tried to explain theoretically the splittings observed in the region of magnetic order. For this purpose a one-particle model has been used to calculate the transition probabilities for the 4f⁷?4f⁶(⁷F _J ) 5dt_2g and the 4f⁷?4f⁶(⁷F _J ) 5de_g transition, taking into account an exchange interaction as well as a spin-orbit coupling. Although this simple model can explain the splittings of the excited 4f⁶(⁷F _J ) 5de_g-state, a complete explanation of the effect of magnetic order on the 4f⁶(⁷F _J ) 5dt_2g-state fails up to now.     

First evidence for a Sm<Superscript>3+</Superscript>-type contribution to the magnetic form factor in the quasielastic spectral response of intermediate valence SmB<Subscript>6</Subscript>

The momentum-transfer dependence of the magnetic form factor associated with the quasielastic spectral component in the dynamic magnetic response of intermediate valence SmB₆ has been measured using inelastic neutron scattering on a double-isotope (¹⁵⁴Sm, ¹¹B) single crystal. The experimental dependence differs qualitatively from those obtained earlier for the inelastic signals, as well as from the field-induced magnetic form factor of SmB₆ obtained by polarized neutron diffraction. This observation is interpreted by specifically considering the Curie-type contributions to the dynamic susceptibility, which arise from the mixing of 4 f⁵ and 4 f⁶J-multiplets into the intermediate valence state wavefunction.     

Oriented O(3P2), Ne(3P2), and He(3S1) atoms emerging from a bent magnetic guide

We describe our observation of strongly oriented total electronic angular momentum J in O(³P₂), Ne(³P₂), and He(³S₁) atoms emerging from a bent magnetic multipole guide, as measured by resonant multiphoton ionisation. This was contrary to our expectation because no additional (uniform) magnetic fields were applied to orient the atoms behind the exit of the guide. Two- and three-photon ionisation techniques were employed to determine the degree of J polarisation, from which we infer that atoms become oriented as a result of a combination of weak fringe fields, possible stray fields, and the fact that molecular beam packets do not oscillate around the geometric center of the bent multipole guide. We conclude that similar effects may exist in other, related experiments and that a detailed characterisation of the degree of orientation is required prior to any study of chemical dynamics or spectroscopy. This paper should serve as a warning for anybody using similar devices not to assume isotropic angular momentum distributions of atoms and molecules emerging from a magnetic guide or a decelerator, particularly when it is bent; whenever possible, the possibility for a J anisotropy should be experimentally checked.     

Valence state and magnetic interactions in magnetically ordered Eu(Pd1−x Au x )2Si2

X-ray diffraction,¹⁵¹Eu Mössbauer effect (ME) and magnetic susceptibility measurements have been performed to investigate the valence behavior and the magnetic interactions of the Eu ions in the intermetallic series Eu(Pd_1–x Au _x )₂Si₂ (0x1) as a Forx>0.4 all experimental techniques are in agreement with each other and suggest a divalent 4f ⁷ ground state of the Eu ion. Belowx=0.4 the different methods lead to different results: while the lattice parameters and the ME isomer shift suggest an instable behavior of the valence the magnetic susceptibility proves a pure divalent 4f ⁷ ground state. These differences can be explained by assuming a partial extension of the 4f-shell radius such that the localized character of the 4f-electrons is preserved.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Zur Frage des Grundzustandes im Tb I-Spektrum

In an atomic beam magnetic resonance experiment on Tb¹⁵⁹ ΔF=0 transitions in several hfs-levels of thermally excited fine structure states have been observed. Detailed analysis of data showed twoJ=15/2 states, oneJ=13/2, oneJ=11/2, and, probably, oneJ=9/2 state to be present. For these levelsg _J-values are given. It was concluded that the ground state of neutral terbium is 4f ⁸ 5d 6s ^{2 8} G _15/2. The 4f ⁹ 6s ^{2 6} H _15/2-level lies not more than 1000 cm^?1 higher.     

Neuropsychological constraints to human data production on a global scale

High-magnetic-field X-ray absorption spectra (XAS) and its X-ray magnetic circular dichroism (XMCD) at the Yb L_2, 3 edges of YbInCu₄ are calculated around the field-induced valence transition at about 30 T. The calculations are made by using a new theoretical framework with an extended single impurity Anderson model (SIAM) developed recently by the present author. Two parameters in SIAM, the 4f level and the hybridization strength, are taken as different values in low- and high-magnetic-field phases of the field-induced valence transition. The calculated results are compared with recent experimental data measured by Matsuda et al. by utilizing a miniature pulsed magnet up to 40 T. The field-dependence of the calculated XMCD spectra is explained in detail on the basis of the field-dependence of the Yb 4f wavefunctions in the ground state. Some possibilities are discussed on the negative XMCD signal observed experimentally at the L₂ edge.     

Crystallographic anisotropy and distortions in helicoidal magnetic structure

The appearance and development of aperiodic distortions in a helicoidal, layered magnetic structure with increasing crystallographic magnetic anisotropy in the magnetization rotation plane have been theoretically studied. A simple phase diagram for this system is proposed. It is established that, at a weak anisotropy, the spiral splits into regions of various lengths with an approximately uniform rotation of the magnetization in each region and a deviation from uniformity at the boundaries; the stronger the anisotropy, the shorter the regions and the greater the deviations. In the limit of high anisotropy, the minimum energy of the system corresponds (depending on the ratio of interlayer exchange integrals J ₁ and J ₂) to either a spiral with constant angular pitch (a multiple of the angle between easy axes) or a double antiferromagnetic structure with a four-layer period. In the case of sixth-order anisotropy with |J ₁| = −J ₂, the energies of phases with different periods (four and six layers for J ₁ > 0; four and three layers for J ₁ < 0) coincide and the excess boundary energy vanishes. In the case of a fourth- and second-order anisotropy, the analogous anomalies appear at |J ₁| = −2J ₂. As a result, the magnetic structure at these points becomes unstable and the phase diagram exhibits the corresponding singularities.     

Phase diagram of the Ising Model on a Cayley tree in the presence of competing interactions and magnetic field

We study the phase diagram for the Ising Model on a Cayley tree with competing nearest-neighbor interactionsJ ₁ and next-nearest-neighbor interactionsJ ₂ andJ ₃ in the presence of an external magnetic field. To perform this study, an iterative scheme similar to that appearing in real space renormalization group frameworks is established; it recovers, as particular cases, previous works by Vannimenus and by Inawashiroet al. At vanishing temperature, the phase diagram is fully determined, for all values and signs ofJ ₂/J ₁ andJ ₃/J ₂; in particular, we verify that values ofJ ₃/J ₂ high enough favor the paramagnetic phase. At finite temperatures, several interesting features (evolution of reentrances, separation of the modulated region into two disconnected pieces, etc.) are exhibited for typical values ofJ ₂/J ₁ andJ ₃/J ₂.Partially supported by the Brazilian Agencies CNPq and FINEP.     

Autoionization spectra of Sm atom

Spectra of autoionizing states of the Sm atom in an energy region between 45948.9 cm-1 and 46943.6 cm-1 are systematically investigated by a three-color multi-step resonant excitation scheme with three different excitation paths.The three intermediate states,4f 66s7s 7F3,4f 66s7s 7F4,and 4f 66s7s 9F5 are employed for the three paths,respectively.Based on precise calibration of wavelength,the level energies of 112 autoionizing states are determined with the line widths and the relative line intensities of the related transitions.The possible influence of configuration interaction on the line shape of autoionizing state is also discussed.In addition,a unique value of J,the total angular momentum,is assigned to all detected states by comparing the three spectra obtained with the different excitation paths.     

Magnetoelastic excitations and structural phase transitions in tetragonal paramagnets

The systematic discussion of the elastic and structural properties of the tetragonal paramagnetic model with the maximum value of the total angular momentumJ=1 in an external magnetic field along thez orx direction is given. The sound velocities of all the symmetry modes are calculated by using the standard perturbation theory and Green's function method. It is shown that only in the presence of the external field directed along thez-axis, for some values of this field and temperature one of the symmetry elastic constantsc ₄₄ orc _B becomes zero and the phase transition to monoclinic (triclinic) or volume change transition can occur.