11,946 research outputs found
Competition between crystalline electric field singlet and itinerant states of f electrons
A new kind of phase transition is proposed for lattice fermion systems with
simplified f^2 configurations at each site. The free energy of the model is
computed in the mean-field approximation for both the itinerant state with the
Kondo screening, and a localized state with the crystalline electric field
(CEF) singlet at each site. The presence of a first-order phase transition is
demonstrated in which the itinerant state changes into the localized state
toward lower temperatures. In the half-filled case, the insulating state at
high temperatures changes into a metallic state, in marked contrast with the
Mott transition in the Hubbard model. For comparison, corresponding states are
discussed for the two-impurity Kondo system with f^1 configuration at each
site.Comment: 10 pages LaTeX , 2 eps figures Accepted for publication in Z.Phys.
Intransitivity in Theory and in the Real World
This work considers reasons for and implications of discarding the assumption
of transitivity, which (transitivity) is the fundamental postulate in the
utility theory of Von Neumann and Morgenstern, the adiabatic accessibility
principle of Caratheodory and most other theories related to preferences or
competition. The examples of intransitivity are drawn from different fields,
such as law, biology, game theory, economics and competitive evolutionary
dynamic. This work is intended as a common platform that allows us to discuss
intransitivity in the context of different disciplines. The basic concepts and
terms that are needed for consistent treatment of intransitivity in various
applications are presented and analysed in a unified manner. The analysis
points out conditions that necessitate appearance of intransitivity, such as
multiplicity of preference criteria and imperfect (i.e. approximate)
discrimination of different cases. The present work observes that with
increasing presence and strength of intransitivity, thermodynamics gradually
fades away leaving space for more general kinetic considerations.
Intransitivity in competitive systems is linked to complex phenomena that would
be difficult or impossible to explain on the basis of transitive assumptions.
Human preferences that seem irrational from the perspective of the conventional
utility theory, become perfectly logical in the intransitive and relativistic
framework suggested here. The example of competitive simulations for the
risk/benefit dilemma demonstrates the significance of intransitivity in cyclic
behaviour and abrupt changes in the system. The evolutionary intransitivity
parameter, which is introduced in the Appendix, is a general measure of
intransitivity, which is particularly useful in evolving competitive systems.
Quantum preferences are also considered in the Appendix.Comment: 44 pages, 14 figures, 47 references, 6 appendice
Competition between Hund's coupling and Kondo effect in a one-dimensional extended periodic Anderson model
We study the ground-state properties of an extended periodic Anderson model
to understand the role of Hund's coupling between localized and itinerant
electrons using the density-matrix renormalization group algorithm. By
calculating the von Neumann entropies we show that two phase transitions occur
and two new phases appear as the hybridization is increased in the symmetric
half-filled case due to the competition between Kondo-effect and Hund's
coupling. In the intermediate phase, which is bounded by two critical points,
we found a dimerized ground state, while in the other spatially homogeneous
phases the ground state is Haldane-like and Kondo-singlet-like, respectively.
We also determine the entanglement spectrum and the entanglement diagram of the
system by calculating the mutual information thereby clarifying the structure
of each phase.Comment: 9 pages, 9 figures, revised version, accepted for publication in PR
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