471 research outputs found
Theory of Unconventional Superconductivity in Strongly Correlated Systems: Real Space Pairing and Statistically Consistent Mean-Field Theory - in Perspective
In this brief overview we discuss the principal features of real space
pairing as expressed via corresponding low-energy (t-J or periodic
Anderson-Kondo) effective Hamiltonian, as well as consider concrete properties
of those unconventional superconductors. We also rise the basic question of
statistical consistency within the so-called renormalized mean-field theory. In
particular, we provide the phase diagrams encompassing the stable magnetic and
superconducting states. We interpret real space pairing as correlated motion of
fermion pair coupled by short-range exchange interaction of magnitude J
comparable to the particle renormalized band energy , where is the
carrier number per site. We also discuss briefly the difference between the
real-space and the paramagnon - mediated sources of superconductivity. The
paper concentrates both on recent novel results obtained in our research group,
as well as puts the theoretical concepts in a conceptual as well as historical
perspective. No slave-bosons are required to formulate the present approach
Conductance of a double quantum dot with correlation-induced wave function renormalization
The zero-temperature conductance of diatomic molecule, modelled as a
correlated double quantum dot attached to noninteracting leads is investigated.
We utilize the Rejec-Ramsak formulas, relating the linear-response conductance
to the ground-state energy dependence on magnetic flux within the framework of
EDABI method, which combines exact diagonalization with ab initio calculations.
The single-particle basis renormalization leads to a strong particle-hole
asymmetry, of the conductance spectrum, absent in a standard parametrized model
study. We also show, that the coupling to leads V=0.5t (t is the hopping
integral) may provide the possibility for interatomic distance manipulation due
to the molecule instability.Comment: Presented on the The International Conference on Strongly Correlated
Electron Systems SCES'05, July 26-30th 2005, Vienna, Austria. An abbreviated
version will appear in Physica
Partial localization of correlated electrons: spin dependent masses, saturated ferromagnetism, and effective s-d model
We determine the localization threshold in a partially filled and orbitally
degenerate model of correlated electrons. Particular emphasis is put on a
non-integer band filling, when the system decomposes into the localized and the
itinerant subsystems; this situation is described by an effective s-d model. A
simultaneous transition to the ferromagnetic state is discussed as driven by
the Hund's rule coupling. Dependence of the quasiparticle mass on the spin
direction appears naturally in the ferromagnetic phase and is attributed to the
electron correlation effects, as is also a metamagnetic transition in an
applied field. Although the main results have been obtained within the saddle
point slave-boson approach, their qualitative features are discussed in general
terms, i.e. as a transition from quantum-mechanical indistinguishability of
particles to the two-component situation. A comparison with the situation for
the orbitally nondegenerate band is also briefly mentioned.Comment: 9 pages, 7 figure
Fifty years of Hubbard and Anderson lattice models: from magnetism to unconventional superconductivity - A brief overview
We briefly overview the importance of Hubbard and Anderson-lattice models as
applied to explanation of high-temperature and heavy-fermion superconductivity.
Application of the models during the last two decades provided an explanation
of the paired states in correlated fermion systems and thus extended
essentially their earlier usage to the description of itinerant magnetism,
fluctuating valence, and the metal-insulator transition. In second part, we
also present some of the new results concerning the unconventional
superconductivity and obtained very recently in our group. A comparison with
experiment is also discussed, but the main emphasis is put on rationalization
of the superconducting properties of those materials within the real-space
pairing mechanism based on either kinetic exchange and/or Kondo-type
interaction combined with the electron correlation effects.Comment: 22 pages, 7 figures, sent to Philosophical Magazin
Universal scaling and quantum critical behavior of CeRhSb(1-x)Sn(x)
We propose a universal scaling rho*chi=const of the electrical resistivity
rho with the inverse magnetic susceptibility chi^(-1) below the temperature of
the quantum-coherence onset for the Ce 4f states in CeRhSb(1-x)Sn(x). In the
regime, where the Kondo gap disappears (x~0.12), the system forms a non-Fermi
liquid (NFL), which transforms into a Fermi liquid at higher temperature. The
NFL behavior is attributed to the presence of a novel quantum critical point
(QCP) at the Kondo insulator - correlated metal boundary. The divergent
behavior of the resistivity, the susceptibility, and the specific heat has been
determined when approaching QCP from the metallic side.Comment: Sent to Phys. Rev. Let
Seebeck effect in the graphene-superconductor junction
Thermopower of graphene-superconductor (GS) junction is analyzed within the
extended Blonder- Tinkham-Klapwijk formalism. Within this approach we have also
calculated the temperature de- pendence of the zero-bias conductance for GS
junction. Both quantities reflect quasi-relativistic nature of massless Dirac
fermions in graphene. Both, the linear and the non-linear regimes are
considered.Comment: 5 pages, 4 figure
Anderson lattice with explicit Kondo coupling: general features and the field-induced suppression of heavy-fermion state in ferromagnetic phase
We apply the extended (statistically-consistent, SGA) Gutzwiller-type
approach to the periodic Anderson model (PAM) in an applied magnetic field and
in the strong correlation limit. The finite-U corrections are included
systematically by transforming PAM into the form with Kondo-type interaction
and residual hybridization, appearing both at the same time. This effective
Hamiltonian represents the essence of \textit{Anderson-Kondo lattice model}. We
show that in ferromagnetic phases the low-energy single-particle states are
strongly affected by the presence of the applied magnetic field. We also find
that for large values of hybridization strength the system enters the so-called
\textit{locked heavy fermion state}. In this state the chemical potential lies
in the majority-spin hybridization gap and as a consequence, the system
evolution is insensitive to further increase of the applied field. However, for
a sufficiently strong magnetic field, the system transforms from the locked
state to the fully spin-polarized phase. This is accompanied by a metamagnetic
transition, as well as by drastic reduction of the effective mass of
quasiparticles. In particular, we observe a reduction of effective mass
enhancement in the majority-spin subband by as much as 20% in the fully
polarized state. The findings are consistent with experimental results for
CeLaB compounds. The mass enhancement for the spin-minority
electrons may also diminish with the increasing field, unlike for the
quasiparticles states in a single narrow band in the same limit of strong
correlations
Statistical properties and statistical interaction for particles with spin: Hubbard model in one dimension and statistical spin liquid
We derive the statistical distribution functions for the Hubbard chain with
infinite Coulomb repulsion among particles and for the statistical spin liquid
with an arbitrary magnitude of the local interaction in momentum space.
Haldane's statistical interaction is derived from an exact solution for each of
the two models. In the case of the Hubbard chain the charge (holon) and the
spin (spinon) excitations decouple completely and are shown to behave
statistically as fermions and bosons, respectively. In both cases the
statistical interaction must contain several components, a rule for the
particles with the internal symmetry.Comment: (RevTex, 16 pages, improved version
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