Konrad Matho - Academia.edu (original) (raw)

Papers by Konrad Matho

Le Journal de Physique Colloques, 1988

The free energy and static spin-correlation function of a two site resonance model akin to the si... more The free energy and static spin-correlation function of a two site resonance model akin to the single site Schotte model are calculated. Thermodynamic functions are discussed and model parameters are linked to those of the microscopic two site Kondo model.

Low Temperature Physics-LT 13, 1974

We have studied conduction electron relaxation in the presence of interacting magnetic impurities... more We have studied conduction electron relaxation in the presence of interacting magnetic impurities by perturbation theory.1

Le Journal de Physique Colloques, 1985

Acta Physica Polonica A, 2000

ARPES integrals are related to the momentum distribution nk. In case of a metal, points kF on the... more ARPES integrals are related to the momentum distribution nk. In case of a metal, points kF on the Fermi surface were identified by: (i) a change of sign in the temperature variation of the ARPES integrals or (ii) maximum slope in its angular variation. These criteria are based on the assumption of particle-hole symmetry in the vicinity of the Fermi edge. Here, we check (i) and (ii) on the level of the momentum distribution, for an electronic structure with most of its incoherent weight below the Fermi edge. Evaluating nk(T) up to Τ Δ*, a Fermi liquid coherence energy, we find: criterion (i) remains stable, while (ii) deviates from kF α m*Τ/kF.

Journal of Non-Crystalline Solids, 1993

Abstract Possible connections between magnetism and atomic structure in AlMn and AlSiMn icosahedr... more Abstract Possible connections between magnetism and atomic structure in AlMn and AlSiMn icosahedral and amorphous phases are critically reviewed. The magnetic entropy, when analyzed in an RKKY model, indicates a strong anticlustering of the spins. This is interpreted in terms of symmetry induced moments with an icosahedral environment around each magnetic site, extending to ≈ three atomic shells. This structural unit is called a “magnetic amorphon”. The role of Si is also discussed in this context.

Journal of Non-Crystalline Solids, 1984

Abstract We discuss evidence, based on resistivity, thermopower (TEP) and susceptibility measurem... more Abstract We discuss evidence, based on resistivity, thermopower (TEP) and susceptibility measurements, for anomalous coupling of the Ce 4f electron and for crystalline electric fields (CEF) in a-Ce X Al 100−X . The Kondo temperature is high towards both ends of the composition range and low in the center. Results are compared with the Kondo lattice behaviour of c-CeAl 3 .

Journal of Magnetism and Magnetic Materials, 1980

Journal de Physique Lettres, 1977

La résistivité électrique d'alliages dilués monoisotopiques d'Au-171Yb et de Au-174Yb a été mesur... more La résistivité électrique d'alliages dilués monoisotopiques d'Au-171Yb et de Au-174Yb a été mesurée jusqu'à 18 mK. Dans l'Au-171Yb, on observe une chute de résistivité en dessous de 90 mK. On montre que cet effet résulte du couplage hyperfin magnétique dans l'171Yb qui lève la dégénérescence des niveaux électronucléaires en produisant un état fondamental singulet et un état excité triplet. On propose un modèle simple qui rend compte des résultats expérimentaux. Abstract.-The electrical resistivities of monoisotopic dilute alloys of Au-171Yb and Au-174Yb have been measured down to 18 mK. A resistivity drop is observed in Au-171Yb, below 90 mK. This effect is shown to result from the magnetic hyperfine coupling in 171Yb which splits the electronuclear levels into a singlet ground state and a triplet excited state. A simple model is proposed which accounts for the experimental results.

Physical Review X, 2015

Strongly correlated electron systems are one of the central topics in contemporary solid-state ph... more Strongly correlated electron systems are one of the central topics in contemporary solid-state physics. Prominent examples for such systems are Kondo lattices, i.e., intermetallic materials in which below a critical temperature, the Kondo temperature T K , the magnetic moments become quenched and the effective masses of the conduction electrons approach the mass of a proton. In Ce-and Yb-based systems, this so-called heavy-fermion behavior is caused by interactions between the strongly localized 4f and itinerant electrons. A major and very controversially discussed issue in this context is how the localized electronic degree of freedom gets involved in the Fermi surface (FS) upon increasing the interaction between both kinds of electrons or upon changing the temperature. In this paper, we show that the FS of a prototypic Kondo lattice, YbRh 2 Si 2 , does not change its size or shape in a wide temperature range extending from well below to far above the single-ion Kondo temperature T K ∼ 25 K of this system. This experimental observation, obtained by means of angle-resolved photoemission spectroscopy, is in remarkable contrast to the widely believed evolution from a large FS, including the 4f degrees of freedom, to a small FS, without the 4f's, upon increasing temperature. Our results explicitly demonstrate a need to further advance in theoretical approaches based on the periodic Anderson model in order to elucidate the temperature dependence of Fermi surfaces in Kondo lattices.

$Research paper thumbnail of Spectral density of the Hubbard model by the continued fraction method$

Physical Review B, 2006

We present the continued fraction method (CFM) as a new microscopic approximation to the spectral... more We present the continued fraction method (CFM) as a new microscopic approximation to the spectral density of the Hubbard model in the correlated metal phase away from half filling. The quantity expanded as a continued fraction is the single particle Green function. Leading spectral moments are taken into account through a set of real expansion coefficients, as known from the projection technique. The new aspect is to add further stages to the continued fraction, with complex coefficients, thus defining a terminator function. This enables us to treat the entire spectral range of the Green function on equal footing and determine the energy scale of the Fermi liquid quasiparticles by minimizing the total energy. The solution is free of phenomenological parameters and remains well defined in the strong coupling limit, near the doping controlled metal-insulator transition. Our results for the density of states agree reasonably with several variants of the dynamical mean field theory. The CFM requires minimal numerical effort and can be generalized in several ways that are interesting for applications to real materials.

Journal of Magnetism and Magnetic Materials, 1986

Journal of Low Temperature Physics, 1982

We present direct measurements of the absolute thermoelectric power of some diluteAuFe alloys at ... more We present direct measurements of the absolute thermoelectric power of some diluteAuFe alloys at very low temperature using a high-sensitivity voltmeter. The experimental results are discussed in the light of the spin-glass versus Kondo competition.

Journal of Magnetism and Magnetic Materials, 1988

Abstract The resistivity ϱ and the susceptibility χ of very small single crystals of CeAl 3 have ... more Abstract The resistivity ϱ and the susceptibility χ of very small single crystals of CeAl 3 have been measured. The anisotropy of χ reflects the magnetic property of the crystal field doublet ground state | J z = ± 3/2〉. At low temperature, both the resistivity and the magnetoresistance provide evidence that some kind of magnetic order starts to develop at 1.6 K.

Journal of Physics F: Metal Physics, 1978

The electrical resistivity of dilute PtMn spin glass alloys (0.05-1.0 at.%) has been measured in ... more The electrical resistivity of dilute PtMn spin glass alloys (0.05-1.0 at.%) has been measured in a temperature range from 0.05 to 10K. All alloys show, in contrast to the maxima in Delta rho (T) normally observed in spin glasses, pronounced minima in the resistivity, with Tmin varies as c. Below Tmin, Delta rho varies 'proportional to T', above Tmin, a positive logarithmic temperature dependence is observed. The total resistivity behaviour can be explained within the cluster model of Matho and Beal-Monod (1972). In addition, the variations of the single impurity limit R(T) for all magnetic Pt 3d alloy systems are reviewed and interpreted within the framework of a spin exchange (Kondo type) model.

Journal of Magnetism and Magnetic Materials, Feb 3, 1992

A so-called Hubbard sum rule determines the weight of a satellite in termionic single-particle ex... more A so-called Hubbard sum rule determines the weight of a satellite in termionic single-particle excitations with strong local repulsion (U ~). Together with the Luttinger sum rule, this imposes two different energy scales on the remaining finite excitations. In the Hubbard chain, this has been identified microscopically as being due to a separation of spin and charge. Lutthzger sum rule. The separation o[ charge and spin degrees of freedom is a ubiquitous phenomenon in the single-particle propagator G(k, co) of lattice fermions with strong local repulsion U. From space dimension d = I [1,2] to d = ~ [3], the total spectrum of excitations above the "normal" electronic groundstate is marked by its resemblance to the single-site Kondo problem [4], iu which this separation first occurs. As the property defining a "normal" state, wc retain the unbroken symmetry among spin channels. In the Hubbard chain [1] and t-J chain [2] the analyticity properties of a l~ermi-hqund state according to Luttinger [5] break down [1,2,6]. Nevertheless, the spin spectrum continues to have a Fermi surface (FS) that follows the Luttinger sum rule (LSR) in k-space. Here, wc assume that the LSR holds, beyond the Fermi liquid fixed point, also in dimcnsions d > 1, whenever there is unbroken symmetry. Hubbard sum rule. Hubbard satellites occur in all modcls with a "configurational crossovcr" [7]. Thc weight of a satellite is givcn by an exact sum rulc, which wc call ttubbard sum rule (HSR). Thc only input nccdcd to derive the HSR, for crossovers of arbitrary configurations, is precisely the unbroken symmetry in their flavours [7]. Electrons in the local configurations participate in the FS. Anderson [6] pointed out that the expulsion of one new excitation into the the satellite for each added barc particle causes the vanishing of the quisiparticle residue in the propagator. As we shall demonstrate, this intimate link between a low-energy phenomenon and a high-energy phenomenon is already present on the crudest level of global sum rules. Considcr thc N = 2 Hubbard model [8] in the filling interval ! <n d < 2, n a= 2m. Thc satellite is then holc-likc and has a wcight Q = i-m per spin channel. This reduccs the weight of holes with finite energy (co<~) to Q~, =2m-1. The particle sector (~o>#) retains its full free-fermion weight Q~, + = 1-m. The total weight for excitations with finite energy, as counted from Ix, is Q~, = Q~, + + Q~, = m, per channel. The Hubbard propagator (HP)was the fir,,;t approximation to G(k, ~) [8,9] that obeyed these exact weights. This justifies to attach Hubbard's na:nc to the

Journal of Electron Spectroscopy and Related Phenomena, Jul 1, 2010

ABSTRACT In this paper we use a generic form for the Green function G(k, ω) in a correlated metal... more ABSTRACT In this paper we use a generic form for the Green function G(k, ω) in a correlated metal, already proven successful in describing ARPES line shapes [1]. The associated many body self-energy function has only a single pole. We now investigate, whether this generic model can be used all the way to the limit of strong correlations and, when applied to ARPES intensities, whether it is able to explain some of the ubiquitous dispersive crossover phenomena that have been attributed to dynamical, i.e.: ω-dependent effects. We argue that a quantitative interpretation of experimental data requires to calculate extrema not only in the momentum distribution curve but also in the energy distribution curve. In passing, we give a formula for the extrema in the latter distribution that is valid for the general G(k, ω) in a many body system. To our knowledge, this is a new formula, not found in the literature. The investigation of the generic model proceeds on two levels: on the one hand, we explore the rich variety of crossovers that can be predicted and linked to well defined features in the complex ω-plain. On the other hand, we show that the generic one-pole self-energy can be viewed as a projection on the low energy sector of a microscopic solution, belonging to a lattice model of interacting fermions. To obtain approximate microscopic solutions, we use our continued fraction method [2] and [3]. As an explicit example, we study the projection for the case of a hole doped Hubbard model in infinite dimension. A discussion section gives examples, how the generic model is able to cope with the ubiquity of the crossover phenomena, also in finite dimension and beyond the Hubbard model.

Physical Review Letters, Jan 13, 2012

We present the theory of an extremely correlated Fermi liquid with U → ∞. This liquid has an unde... more We present the theory of an extremely correlated Fermi liquid with U → ∞. This liquid has an underlying auxiliary Fermi liquid Greens function that is further caparisoned by extreme correlations. The theory leads to two parallel hierarchies of equations that permit iterative approximations in a certain parameter. Preliminary results for the spectral functions display a broad background and a distinct T dependent left skew. An important energy scale ∆(k, x) emerges as the average inelasticity of the FL Greens function, and influences the photoemission spectra profoundly. A duality is identified wherein a loss of coherence of the ECFL results from an excessively sharp FL.

Journal of Electron Spectroscopy and Related Phenomena, Jun 1, 2001

ABSTRACT An interpolation formula, connecting the high and low energy expansions of a momentum re... more ABSTRACT An interpolation formula, connecting the high and low energy expansions of a momentum resolved Green function G(k, ω) was first outlined in: K. Matho, J. Phys. Chem. Solids 56 (1995) 1735. Here, the algorithm is presented in detail, allowing to calculate the interpolated spectrum for all energies. The high energy part is given by a Padé approximant of arbitrary order. The low energy scenario, with a large Fermi surface, is either backed up by microscopic manybody theory or suggested by phenomenological considerations. The algorithm itself decides, whether the two scenarios to be interpolated are compatible with each other. As an application, we give an in depth discussion of a correlated photohole, as observable in photoemission experiments. The emphasis is on experimental and theoretical exploration of generic low energy features, in agreement with the overall electronic structure of real materials. The context of doped, metallic Mott–Hubbard systems is chosen to indicate ways of modeling correlated spectra in the presence of strong onsite repulsion U and in finite dimension d=2 or d=3.