11,988 research outputs found
Scaling analysis of a model Hamiltonian for Ce impurity in a cubic metal
We introduce various exchange interactions in a model Hamiltonian for
Ce ions in cubic symmetry with three configurations (,,).
With the impurity pseudo spin , our Hamiltonian includes: (i)
One-channel Anderson model; (ii) Two-channel Anderson
model; (iii) An unforseen one-channel Anderson model with a
non-trivial fixed point; (iv) Mixing exchange interaction between the
and the conduction electron partial wave states; (v)
Multiple conduction electron partial wave states. Using the third-order scaling
(perturbative renormalization group) analysis, we study stability of various
fixed points relevant to various exchange interactions for Ce ions in
cubic symmetry.Comment: 68 pages. 4 figures are available upon request from
[email protected] (revised
Two-channel Kondo Lattice Model on a ladder studied by the Density Matrix Renormalization Group Method
Using the density matrix renormalization group (DMRG) method we study a
two-channel Kondo lattice model on a half filled ladder. Our model involves an
on-site s-wave and a nearest neighbor d-wave coupling between the local moments
and the conduction electrons on the ladder. By changing the relative strength
of the two Kondo interactions we examine the evolution of the system from a
conventional Kondo insulator with a singlet at each site to a new kind of
semimetallic state formed by overlapping of Zhang-Rice-like singlets. The DMRG
is used to study how the spin and charge correlation functions evolve between
these two regimes
Specific Heat of a Three Dimensional Metal Near a T=0 Magnetic Transition with Dynamic Exponent z=2,3,4
We derive expressions for the universal contribution to the specific heat of
a three-dimensional metal near a zero-temperature phase transition with dynamic
exponent , or 4. The results allow a quantitative comparison of theory
to data. We illustrate the application of our results by analyzing data for
CeLuCuSi, which has been claimed to be near a quantum
critical point.Comment: 23 pages, revtex. For figures, send mail to [email protected]
From ferromagnetism to spin-density wave: Magnetism in the two channel periodic Anderson model
The magnetic properties of the two-channel periodic Anderson model for
uranium ions, comprised of a quadrupolar and a magnetic doublet are
investigated through the crossover from the mixed-valent to the stable moment
regime using dynamical mean field theory. In the mixed-valent regime
ferromagnetism is found for low carrier concentration on a hyper-cubic lattice.
The Kondo regime is governed by band magnetism with small effective moments and
an ordering vector \q close to the perfect nesting vector. In the stable
moment regime nearest neighbour anti-ferromagnetism dominates for less than
half band filling and a spin density wave transition for larger than half
filling. is governed by the renormalized RKKY energy scale \mu_{eff}^2
^2 J^2\rho_0(\mu).Comment: 4 pages, RevTeX, 3 eps figure
Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTiAl
The cubic compound PrTiAl is a quadrupolar Kondo lattice system
that exhibits quadrupolar ordering due to the non-Kramers ground
doublet and has strong hybridization between and conduction electrons. Our
study using high-purity single crystal reveals that PrTiAl exhibits
type-II superconductivity at mK in the nonmagnetic
ferroquadrupolar state. The superconducting critical temperature and field
phase diagram suggests moderately enhanced effective mass of
Spin Dynamics in the Magnetic Chains Arrays of Sr14Cu24O41: a Neutron Inelastic scattering Investigation
Below about 150 K, the spin arrangement in the chain arrays of Sr14Cu24O41 is
shown to develop in two dimensions (2D). Both the correlations and the
dispersion of the observed elementary excitations agree well with a model of
interacting dimers. Along the chains, the intra- and inter-dimer distances are
equal to 2 and about 3 times the distance (c) between neighboring Cu ions.
While the intra-dimer coupling is J about 10 meV, the inter-dimer couplings
along and between the chains are of comparable strenght, J// about -1.1 meV and
Jperp about 1.7 meV, respectively. This remarkable 2D arrangement satisfies the
formal Cu valence of the undoped compound. Our data suggest also that it is
associated with a relative sliding of one chain with respect to the next one,
which, as T decreases, develops in the chain direction. A qualitative analysis
shows that nearest inter-dimer spin correlations are ferromagnetic, which, in
such a 2D structure, could well result from frustration effects.Comment: 4 pages, 5 figures, submitted to Phys.Rev.B, date of receipt 29 June
199
Mixed valency in cerium oxide crystallographic phases: Determination of valence of the different cerium sites by the bond valence method
We have applied the bond valence method to cerium oxides to determine the
oxidation states of the Ce ion at the various site symmetries of the crystals.
The crystals studied include cerium dioxide and the two sesquioxides along with
some selected intermediate phases which are crystallographically well
characterized. Our results indicate that cerium dioxide has a mixed-valence
ground state with an f-electron population on the Ce site of 0.27 while both
the A- and C-sesquioxides have a nearly pure f^1 configuration. The Ce sites in
most of the intermediate oxides have non-integral valences. Furthermore, many
of these valences are different from the values predicted from a naive
consideration of the stoichiometric valence of the compound
Discovery of a double ring in the core of η Carinae
We report the discovery of a double ring structure in the waist of the nebula surrounding η Carinae. The rings are detected in the mid-IR dust continuum at wavelengths of 7.9, 11.9, 12.9 and 20 μm. The dust in the rings has a temperature of about 300 K. The orientation of the rings is inclined with respect to the axis of the homunculus by either 37 or 58 degrees. The central star is not in the projected centre of the structure defined by the two rings. This geometry is reminiscent of that seen in SN1987A and some planetary nebulae. We discuss several possible origins for this remarkable geometry and its orientation
Non Fermi Liquid Behaviour near a spin-glass transition
In this paper we study the competition between the Kondo effect and RKKY
interactions near the zero-temperature quantum critical point of an Ising-like
metallic spin-glass. We consider the mean-field behaviour of various physical
quantities. In the `quantum- critical regime' non-analytic corrections to the
Fermi liquid behaviour are found for the specific heat and uniform static
susceptibility, while the resistivity and NMR relaxation rate have a non-Fermi
liquid dependence on temperature.Comment: 15 pages, RevTex 3.0, 1 uuencoded ps. figure at the en
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