1,377 research outputs found
On the Critical Behavior of the Uniform Susceptibility of a Fermi Liquid Near an Antiferromagnetic Transition with Dynamic Exponent
We compute the leading behavior of the uniform magnetic susceptibility,
, of a Fermi liquid near an antiferromagnetic transition with dynamic
exponent . Our calculation clarifies the role of triangular ``anomaly''
graphs in the theory and justifies the effective action used in previous work
\cite{Hertz}. We find that at the critical point of a two dimensional
material, with and
nonuniversal constants. For reasonable band structures we find that in a
weak coupling approximation is small and positive. Our result suggests that
the behavior observed in the quantum critical regime of underdoped high-
superconductors are difficult to explain in a theory.Comment: 12 pages, uuencoded Postscript fil
On the Fermi Liquid to Polaron Crossover II: Double Exchange and the Physics of "Colossal" Magnetoresistance
We use the dynamical mean field method to study a model of electrons
Jahn-Teller coupled to localized classical oscillators and ferromagnetically
coupled to ``core spins'', which, we argue, contains the essential physics of
the ``colossal magnetoresistance'' manganites . We
determine the different regimes of the model and present results for the
temperature and frequency dependence of the conductivity, the electron spectral
function and the root mean square lattice parameter fluctuations. We compare
our results to data, and give a qualitative discussion of important physics not
included in the calculation. Extensive use is made of results from a companion
paper titled: ``On the Fermi Liquid to Polaron Crossover I: General Results''.Comment: 34 pages, 10 figures. Depends on previous paper titled "On the Fermi
Liquid to Poalron Crossover I: General Result
On the optical conductivity of Electron-Doped Cuprates I: Mott Physics
The doping and temperature dependent conductivity of electron-doped cuprates
is analysed. The variation of kinetic energy with doping is shown to imply that
the materials are approximately as strongly correlated as the hole-doped
materials. The optical spectrum is fit to a quasiparticle scattering model;
while the model fits the optical data well, gross inconsistencies with
photoemission data are found, implying the presence of a large, strongly doping
dependent Landau parameter
Optical spectral weights and the ferromagnetic transition temperature of CMR manganites: relevance of double-exchange to real materials
We present a thorough and quantitative comparison of double-exchange models
to experimental data on the colossal magnetoresistance manganese perovskites.
Our results settle a controversy by showing that physics beyond double-exchange
is important even in LaSrMnO, which has been regarded as a
conventional double-exchange system. We show that the crucial quantity for
comparisons of different calculations to each other and to data is the
conduction band kinetic energy , which is insensitive to the details of the
band structure and can be experimentally determined from optical conductivity
measurements. The seemingly complicated dependence of on the Hund's
coupling and carrier concentration is shown to reflect the variation of
with , and temperature. We present results for the optical
conductivity which allow interpretation of experiments and show that a feature
previously interpreted in terms of the Hund's coupling was misidentified. We
also correct minor errors in the phase diagram presented in previous work.Comment: 13 pages, 7 eps figure
Anomalous Shift of Chemical Potential in the Double-Exchange Systems
Double-exchange system is investigated by the dynamical mean-field theory. We
show that the chemical potential shifts as a function of temperature and
magnetization, which is anomalously large. We also discuss the influences of
dynamic Jahn-Teller effect to the shift of the chemical potential. Measurement
of the shift of the chemical potential casts a constraint to theoretical
approaches for the magnetoresistance phenomena in (,)MnO such as
double-exchange effects and dynamic Jahn-Teller effects. We also propose a
method to measure the shift of .Comment: Reference added, to be published in J. Phys. Soc. Jpn. Vol. 66 No.8
(Aug. 1997
Dynamic Jahn-Teller Effect and Colossal Magnetoresistance in
A model for which incorporates the physics of dynamic
Jahn-Teller and double-exchange effects is presented and solved via a dynamical
mean field approximation. In an intermediate coupling regime the interplay of
these two effects is found to reproduce the behavior of the resistivity and
magnetic transition temperature observed in .Comment: 11 pages. Latex. Minor revisions, including improvement of discussion
of state with frozen-in lattice distortion. Figures (available from
[email protected]) unchange
T=0 Phase Diagram of the Double-Exchange Model
We present the T=0 phase diagram of the double-exchange model (ferromagnetic
Kondo lattice model) for all values of the carrier concentration and Hund's
couplng , within dynamical mean field theory. We find that depending on the
values of and , the ground state is either a ferromagnet, a commensurate
antiferromagnet or some other incommensurate phase with intermediate wave
vectors . The antiferromagnetic phase is separated by first order phase
boundaries and wide regimes of phase separation. The transition from the
ferromagnetic phase to an incommensurate phase is second order.Comment: 4 pages, 5 figures. The analysis now includes incommensurate phases
with arbitrary wave vectors. Correspondingly, the figures have been change
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