共查询到20条相似文献,搜索用时 15 毫秒
1.
M. S. Figueira R. Franco 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(1):1-10
In this paper we study the low temperature (T) properties of the Kondo insulator FeSi within the X-boson approach. We show
that the ground state of the FeSi is metallic and highly correlated with a large effective mass; the low temperature contributions
to the specific heat and the resistivity are of the Fermi-liquid type. The low temperature properties are governed by a reentrant
transition into a metallic state, that occurs when the chemical potential crosses the gap and enters the conduction band,
generating a metallic ground state. The movement of the chemical potential is due to the strong correlations present in the
system. We consider the low temperature regime of the Kondo insulator FeSi, where the hybridization gap is completely open.
In this situation we identify the two characteristic temperatures: the coherence temperature T0 and the Kondo temperature TKL. In the range T < T0, we identify a regime characterized by the formation of coherent states and Fermi-liquid behavior of the low temperature
properties; in the range TKL > T > T0, we identify a regime characterized by an activation energy. Within the X-boson approach we study those low temperature regimes
although we do not try to adjust parameters to recover the experimental energy scales. 相似文献
2.
B. Andraka R. Pietri S.G. Thomas G.R. Stewart E.-W. Scheidt T. Schreiner 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):55-59
A comprehensive study of the relationship between the electronic specific heat coefficient () and the temperature square coefficient (A) of the electrical resistivity for a single, cubic, heavy fermion alloy system, UPt5-xAux is presented. In this alloy system, whose low temperature properties are consistent with the Fermi-liquid behavior, varies by more than a factor of 10 while the corresponding A coefficient changes by a factor larger than 200. A tracks changes in fairly well, but , postulated to have a universal value for heavy fermions, is not constant and varies from about 10-6 (x = 0, 0.5) to 10-5
cm (mol K/mJ)2 (x
> 1.1), thus from a value typical of transition metals to that characteristic of other heavy fermion compounds. We have found a
correlation between and magnetic characteristics such as the paramagnetic Curie-Weiss temperature and the low temperature magnetic susceptibility
divided by .
Received 29 January 1999 相似文献
3.
T. Sommer 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):315-327
The one-dimensional Kondo lattice model is investigated by means of Wegner's
flow equation method. The renormalization procedure leads to an effective
Hamiltonian which describes a free one-dimensional electron gas and a
Heisenberg chain. The localised spins of the effective model are coupled by
the well-known RKKY interaction. They are treated within a Schwinger boson
mean field theory which permits the calculation of static and dynamic
correlation functions. In the regime of small interaction strength static
expectation values agree well with the expected Luttinger liquid
behaviour. The parameter Kρ of the Luttinger liquid theory is estimated
and compared to recent results from density matrix renormalization group
studies. 相似文献
4.
P. Nozières 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):447-457
The so called exhaustion problem occurs when few electrons have to screen many spins in a metal with magnetic impurities.
A singlet Fermi liquid ground state is possible only if all impurities are “isotropized” in such a way as to suppress their
entropy. That takes a time and the corresponding energy limits the Fermi liquid range. The present note explores that issue of time and energy scales, and it concludes that is much smaller than the single impurity Kondo temperature. Similarly the relevant energy scale is proportional to the number
of electrons. Recent results on the Mott metal insulator transition in infinite dimension are reconsidered in the light of
these results: controversies in that respect are shown to reduce to a simple physical question, with no firm answer as to
now.
Received: 5 May 1998 / Received in final form and Accepted: 29 July 1998 相似文献
5.
P. Bonville E. Vincent E. Bauer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):363-369
We present measurements in the YbCu5-xAlx series, down to the 50 mK range, using 170Yb M?ssbauer absorption spectroscopy and magnetisation measurements. In this series, the hybridisation between the Yb 4
f electrons and the conduction electrons is known to decrease as the Al content x increases. We apply the variational solution of the impurity Kondo problem to the interpretation of our data. We show that
the Kondo temperature can be derived from the measured 4
f quadrupole moment and, for the magnetically ordered compounds (), we obtain the exchange energy as a function of the Al content. Our findings are in general agreement with Doniach's model
describing the onset of magnetic ordering according to the relative values of the Kondo and exchange energy scales.
Received 16 April 1998 相似文献
6.
D. Meyer W. Nolting 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):385-395
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 correct high-energy expansion of the self-energy is essential. Inclusion of damping
effects reduces stability of the ferromagnetic phase.
Received 5 June 2000 and Received in final form 3 August 2000 相似文献
7.
S.G. Magalh aes A.A. Schmidt A. Theumann B. Coqblin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):419-425
The Kondo lattice model has been analyzed in the presence of a random inter-site interaction among localized spins with non
zero mean J0 and standard deviation J. Following the same framework previously introduced by us, the problem is formulated in the path integral formalism where
the spin operators are expressed as bilinear combinations of Grassmann fields. The static approximation and the replica symmetry
ansatz have allowed us to solve the problem at a mean field level. The resulting phase diagram displays several phase transitions
among a ferromagnetically ordered region,a spin glass one, a mixed phase and a Kondo state depending on J0, J and its relation with the Kondo interaction coupling JK. These results could be used to address part of the experimental data for the CeNi
1 - x
Cu
x compound, when x ⩽ 0.8.
Received 24 June 2002 Published online 31 December 2002 相似文献
8.
9.
A. K. Zhuravlev V. Yu. Irkhin M. I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):377-382
Using the numerical renormalization group method, the dependences on
temperature of the magnetic susceptibility χ(T) and specific heat C(T)
are obtained for the single-impurity Anderson model with inclusion of
d-f the Coulomb interaction. It is shown that the exciton effects
caused by this effect (charge fluctuations) can significantly change the
behaviour of C(T) in comparison with the standard Anderson model at
moderately low temperatures, whereas the behaviour of χ(T) remains nearly
universal. The ground-state and temperature-dependent renormalizations of the
effective hybridization parameter and f-level position caused by the
d-f interaction are calculated, and satisfactory agreement with the
Hartree-Fock approximation is derived. 相似文献
10.
H. A. Razafimandimby D. Randrianasoloharisoa A. Rakotomahevitra J. C. Parlebas 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(4):495-500
In Rare-Earth (RE) systems, direct overlapping of 4f orbitals plays a role if the distance between RE ions is sufficiently
small. Especially, such a situation happens under pressure for RE metals and RE compounds. Furthermore, in Actinide systems,
5f orbitals are more extended than the previously considered 4f orbitals. Therefore, in this case, direct overlapping of 5f
orbitals should be taken into account even without applying pressure. In the present work, using Standard Basis Operators,
we study direct overlapping effect of f orbitals for valence fluctuating materials in Kondo regime. An important result within
our present model is that direct f orbital overlapping reduces f electron effective mass. 相似文献
11.
A. Hübsch K. W. Becker 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):345-353
A very rich phase diagram has recently been found in CeCu2Si2 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 f occupation in agreement with
experiment. This valence transition can possibly be interpreted as a
collapse of the large Fermi surface of the heavy fermion state which
incorporates not only the conduction electrons but also the localized
f electrons. The theoretical approach used in this paper
is based on the novel projector-based renormalization method (PRM). With
respect to the periodic Anderson model, the method was before only employed
in combination with the basic approximations of the well-known slave-boson
mean-field theory. In this paper, the PRM treatment is performed in a more
sophisticated manner where both mixed as well as integral valent solutions
have been obtained. Furthermore, we argue that the presented PRM approach
might be a promising starting point to study the competing interactions in
CeCu2Si2 and related compounds. 相似文献
12.
M.A. Continentino 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):31-35
Recently we have shown that a one-parameter scaling, , describes the physical behavior of several heavy fermions in a region of their phase diagram. In this paper we fully characterize
this region, obtaining the uniform susceptibility, the resistivity and the specific heat in terms of the coherence temperature
. This allows for an explicit evaluation of the Wilson and the Kadowaki-Woods ratios in this regime. These quantities turn
out to be independent of the distance to the quantum critical point (QCP). The theory of the one-parameter scaling corresponds to a local interacting model. Although
spatial correlations are irrelevant in this case, time fluctuations are critically correlated as a consequence of the quantum
character of the transition.
Received 23 December 1998 and Received in final form 10 June 1999 相似文献
13.
14.
P. Schlottmann A.A. Zvyagin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):325-335
We consider the one-dimensional t
-
J model, which consists of electrons with spin S on a lattice with nearest neighbor hopping t constrained by the excluded multiple occupancy of the lattice sites and spin-exchange J between neighboring sites. The model is integrable at the supersymmetric point, J
=
t. Without spoiling the integrability we introduce an Anderson-like impurity of spin S (degenerate Anderson model in the limit), which interacts with the correlated conduction states of the host. The lattice model is defined by the scattering
matrices via the Quantum Inverse Scattering Method. We discuss the general form of the interaction Hamiltonian between the impurity and
the itinerant electrons on the lattice and explicitly construct it in the continuum limit. The discrete Bethe ansatz equations
diagonalizing the host with impurity are derived, and the thermodynamic Bethe ansatz equations are obtained using the string
hypothesis for arbitrary band filling as a function of temperature and external magnetic field. The properties of the impurity
depend on one coupling parameter related to the Kondo exchange coupling. The impurity can localize up to one itinerant electron
and has in general mixed valent properties. Groundstate properties of the impurity, such as the energy, valence, magnetic
susceptibility and the specific heat coefficient, are discussed. In the integer valent limit the model reduces to a Coqblin-Schrieffer impurity.
Received: 31 December 1997 / Accepted: 17 March 1998 相似文献
15.
J.I. Espeso J. García Soldevilla J.A. Blanco J. Rodríguez Fernández J.C. Gómez Sal M.T. Fernández Díaz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):625-632
The ground state of the strongly correlated electron CeNi1-xCux compounds has been investigated by means of neutron scattering experiments. Thus, magnetic diffraction was performed for
compounds showing long-range magnetic order (x
> 0.2). An evolution from a collinear ferromagnetic structure for x
=0.6 to a simple antiferromagnetic one for CeCu takes place through some more complex magnetic structures for intermediate compositions.
The magnetic moments are continuously reduced when the Ni content increases reflecting the progressive enhancement of the
Kondo screening. The large reduction found for x
=0.6 compound is discussed and the existence of a spin glass like component of the magnetic moment cannot be discarded. From the
quasielastic spectra, we have obtained the Kondo temperatures which are close to the magnetic ordering ones. The quasielastic
line-width evolves from a linear temperature dependence to a T
1/2
behaviour when approaching the non-magnetic limit. Then, this system provides an interesting example for the evolution of
unstable 4
f shell relaxation regimes when modifying the hybridisation strength.
Received 22 May 2000 相似文献
16.
The electronic band structure of YbRhSn has been calculated using
the self-consistent full potential nonorthogonal local orbital minimum
basis scheme based on the density functional theory. We investigated
the electronic structure with the spin-orbit interaction and on-site
Coulomb potential for the Yb-derived 4f orbitals to obtain the correct
ground state of YbRhSn.
The exchange interaction between local f electrons and conduction
electrons play an important role in the heavy fermion characters of them.
The fully relativistic band structure scheme
shows that spin-orbit coupling splits the 4f states
into two manifolds, the 4f7/2 and the 4f5/2 multiplet. 相似文献
17.
H. von Löhneysen A. Neubert T. Pietrus A. Schröder O. Stockert U. Tutsch M. Loewenhaupt A. Rosch P. Wölfle 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):447-455
We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu6-xAux single crystals for x
> 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector (0.625
0.275) for x
=0.2, nearly unchanged for x
=0.3, and (0.59) for x
=0.5, staying roughly the same for x
=1.0. In addition, short-range correlations are observed for x
=0.2, reminiscent of those found previously for x
=0.1. The ordered magnetic moment is found to increase rapidly for small x, and more slowly for the larger x values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord with this behavior. Finally, data of the electrical resistivity for current flow along the three
crystallographic directions are presented, showing a clear signature of the magnetic order. A theoretical interpretation of
the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered
magnetization and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data,
provided the ordering vector is close to 2
k
F, where k
F is a typical Fermi momentum.
Received: 20 February 1998 / Accepted: 17 April 1998 相似文献
18.
M.Yu. Kagan D.I. Khomskii M.V. Mostovoy 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):217-223
We study the competition between different possible ground states of the double-exchange model with strong ferromagnetic exchange
interaction between itinerant electrons and local spins. Both for classical and quantum treatment of the local spins the homogeneous
canted state is shown to be unstable against a phase separation. The conditions for the phase separation into the mixture
of the antiferromagnetic and ferromagnetic/canted states are given. We also discuss another possible realization of the phase-separated
state: ferromagnetic polarons embedded into an antiferromagnetic surrounding. The general picture of a percolated state, which
emerges from these considerations, is discussed and compared with results of recent experiments on doped manganaties.
Received 17 March 1999 相似文献
19.
A. C. Varghese C. S. Menon 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):465-468
The various electrical properties and the nature of conduction mechanisms of
magnesium phthalocyanine thin film devices with top and bottom aluminium
electrodes have been investigated. The conduction mechanism was identified
as injection limited essentially due to the electrode material. Even with
the same electrode materials, the device showed asymmetric conduction
behavior in the forward and reverse bias. In general the conduction was
interpreted as a Schottky emission with barrier height Φs=1.07 eV for
the forward bias and Φs=1.09 eV in the reverse bias. The effect of
oxygen on the conductivity of the device has also been investigated. In the
oxygen doped samples the conductivity is decreased which may be attributed
to an interfacial layer between the electrode and the organic layer. Further
in the oxygen doped sample while a Schottky emission is observed at lower
voltages Poole-Frenkel conductivity was identified in the higher voltage
region. 相似文献
20.
G. Savona D.V. Livanov A.A. Varlamov 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):415-420
We study the fluctuation-induced magnetotransport of a two-dimensional superconductor in the quasiballistic regime, where
ξ
GL(T) ≪ ℓ (ℓ is the electron mean free path and ξ
GL(T) is the Ginzburg-Landau coherence length). The magnetoconductivity is evaluated in the nonlocal fluctuation regime thereby
extending the existing theory valid in the local limit. We show that the Maki-Thompson (MT) and density-of-states (DOS) contributions
strongly compensate each other and their sum is negligible in comparison with the Aslamazov-Larkin (AL) term. The hierarchy
of the fluctuation contributions to the magnetoconductivity in the high-field limit is also qualitatively discussed.
Received 10 July 2002 / Received in final form 21 November 2002 Published online 7 May 2003 相似文献