3,457 research outputs found
Quadrupole Susceptibility of Gd-Based Filled Skutterudite Compounds
It is shown that quadrupole susceptibility can be detected in Gd compounds
contrary to our textbook knowledge that Gd ion induces pure spin moment
due to the Hund's rules in an coupling scheme. The ground-state multiplet
of Gd is always characterized by =7/2, where denotes total
angular momentum, but in a - coupling scheme, one electron in =7/2
octet carries quadrupole moment, while other six electrons fully occupy =5/2
sextet, where denotes one-electron total angular momentum. For realistic
values of Coulomb interaction and spin-orbit coupling, the ground-state
wavefunction is found to contain significant amount of the - coupling
component. From the evaluation of quadrupole susceptibility in a simple
mean-field approximation, we point out a possibility to detect the softening of
elastic constant in Gd-based filled skutterudites.Comment: 8 pages, 4 figure
Electric Dipolar Susceptibility of the Anderson-Holstein Model
The temperature dependence of electric dipolar susceptibility \chi_P is
discussed on the basis of the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) technique. Note that P is related with
phonon Green's function D. In order to obtain correct temperature dependence of
P at low temperatures, we propose a method to evaluate P through the Dyson
equation from charge susceptibility \chi_c calculated by the NRG, in contrast
to the direct NRG calculation of D. We find that the irreducible charge
susceptibility estimated from \chi_c agree with the perturbation calculation,
suggesting that our method works well.Comment: 4 pages, 4 figure
Electron Mass Enhancement due to Anharmonic Local Phonons
In order to understand how electron effective mass is enhanced by anharmonic
local oscillation of an atom in a cage composed of other atoms, i.e., {\it
rattling}, we analyze anharmonic Holstein model by using a Green's function
method. Due to the evaluation of an electron mass enhancement factor , we
find that becomes maximum when zero-point energy is comparable with
potential height at which the amplitude of oscillation is rapidly enlarged.
Cooperation of such quantum and rattling effects is considered to be a key
issue to explain the electron mass enhancement in electron-rattling systems.Comment: 3 pages, 3 figures, to appear in J. Phys. Soc. Jpn. Suppl.
(Proceedings for International Conference on Heavy Electrons
Kondo Effect in an Electron System with Dynamical Jahn-Teller Impurity
We investigate how Kondo phenomenon occurs in the Anderson model dynamically
coupled with local Jahn-Teller phonons. It is found that the total angular
moment composed of electron pseudo-spin and phonon angular moments is screened
by conduction electrons. Namely, phonon degrees of freedom essentially
contribute to the formation of singlet ground state. A characteristic
temperature of the Kondo effect due to dynamical Jahn-Teller phonons is
explained by an effective - Hamiltonian with anisotropic exchange
interaction obtained from the Jahn-Teller-Anderson model in a non-adiabatic
region.Comment: 5 pages, 3 figure
Filling dependence of a new type of charge ordered liquid on a triangular lattice system
We study the recently reported characteristic gapless charge ordered state in
a spinless fermion system on a triangular lattice under strong inter-site
Coulomb interactions. In this state the charges are spontaneously divided into
solid and liquid component, and the former solid part aligns in a Wigner
crystal manner while the latter moves among them like a pinball. We show that
such charge ordered liquid is stable over a wide range of filling, ,
and examine its filling dependent nature.Comment: 3 pages 3 figure
Multipole as -Electron Spin-Charge Density in Filled Skutterudites
It is shown that -electron multipole is naturally defined as spin-charge
one-electron density operator in the second-quantized form with the use of
tensor operator on the analogy of multipole expansion of electromagnetic
potential from charge distribution in electromagnetism. Due to this definition
of multipole, it is possible to determine multipole state from a microscopic
viewpoint on the basis of the standard linear response theory for multipole
susceptibility. In order to discuss multipole properties of filled
skutterudites, we analyze a seven-orbital impurity Anderson model by employing
a numerical renormalization group method. We show our results on possible
multipole states of filled skutterudite compounds.Comment: To appear in the Proceedings of International Conference on "New
Quantum Phenomena in Skutterudite and Related Systems" (September 2007, Kobe,
Japan
Effective Crystalline Electric Field Potential in a j-j Coupling Scheme
We propose an effective model on the basis of a - coupling scheme to
describe local -electron states for realistic values of Coulomb interaction
and spin-orbit coupling , for future development of microscopic
theory of magnetism and superconductivity in -electron systems, where
is the number of local electrons. The effective model is systematically
constructed by including the effect of a crystalline electric field (CEF)
potential in the perturbation expansion in terms of . In this paper,
we collect all the terms up to the first order of . Solving the
effective model, we show the results of the CEF states for each case of
=25 with symmetry in comparison with those of the Stevens
Hamiltonian for the weak CEF. In particular, we carefully discuss the CEF
energy levels in an intermediate coupling region with in the order
of 0.1 corresponding to actual -electron materials between the and
- coupling schemes. Note that the relevant energy scale of is the
Hund's rule interaction. It is found that the CEF energy levels in the
intermediate coupling region can be quantitatively reproduced by our modified
- coupling scheme, when we correctly take into account the corrections in
the order of in addition to the CEF terms and Coulomb interactions
which remain in the limit of =. As an application of the
modified - coupling scheme, we discuss the CEF energy levels of filled
skutterudites with symmetry.Comment: 12 pages, 7 figures. Typeset with jpsj2.cl
Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon
We discuss Kondo behavior of a conduction electron system coupled with local
optical phonon by analyzing the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) method. There appear three typical
regions due to the balance between Coulomb interaction and
phonon-mediated attraction . For , we
observe the standard Kondo effect concerning spin degree of freedom. Since the
Coulomb interaction is effectively reduced as , the
Kondo temperature is increased when is increased. On
the other hand, for , there occurs the Kondo effect
concerning charge degree of freedom, since vacant and double occupied states
play roles of pseudo-spins. Note that in this case, is decreased
with the increase of . Namely, should be maximized for
. Then, we analyze in detail the Kondo behavior
at , which is found to be explained by the polaron
Anderson model with reduced hybridization of polaron and residual repulsive
interaction among polarons. By comparing the NRG results of the polaron
Anderson model with those of the original Anderson-Holstein model, we clarify
the Kondo behavior in the competing region of .Comment: 8 pages, 8 figure
Nonabelian Duality and Higgs Multiplets in Supersymmetric Grand Unified Theories
We consider strongly interacting supersymmetric gauge theories which break
dynamically the GUT symmetry and produce the light Higgs doublets naturally.
Two models we proposed in the previous articles are reanalyzed as two phases of
one theory and are shown to have desired features. Furthermore, employing
nonabelian duality proposed recently by Seiberg, we study the dual theory of
the above one and show that the low-energy physics of the original and dual
models are the same as expected. We note that the Higgs multiplets in the
original model are regarded as composite states of the elementary hyperquarks
in its dual theory. Theories with other hypercolors and similar matter contents
are also analyzed in the same way.Comment: 16 pages, LaTeX, no figur
Dimensional tuning of electronic states under strong and frustrated interactions
We study a model of strongly interacting spinless fermions on an anisotropic
triangular lattice. At half-filling and the limit of strong repulsive
nearest-neighbor interactions, the fermions align in stripes and form an
insulating state. When a particle is doped, it either follows a one-dimensional
free motion along the stripes or fractionalizes perpendicular to the stripes.
The two propagations yield a dimensional tuning of the electronic state. We
study the stability of this phase and derive an effective model to describe the
low-energy excitations. Spectral functions are presented which can be used to
experimentally detect signatures of the charge excitations.Comment: 4pages 4figures included. to appear in Phys. Rev. Lett. vol. 10
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