6,450 research outputs found
Doping Dependence of Polaron Hopping Energies in La(1-x)Ca(x)MnO(3) (0<= x<= 0.15)
Measurements of the low-frequency (f<= 100 kHz) permittivity at T<= 160 K and
dc resistivity (T<= 430 K) are reported for La(1-x)Ca(x)MnO(3) (0<= x<= 0.15).
Static dielectric constants are determined from the low-T limiting behavior of
the permittivity. The estimated polarizability for bound holes ~ 10^{-22}
cm^{-3} implies a radius comparable to the interatomic spacing, consistent with
the small polaron picture established from prior transport studies near room
temperature and above on nearby compositions. Relaxation peaks in the
dielectric loss associated with charge-carrier hopping yield activation
energies in good agreement with low-T hopping energies determined from
variable-range hopping fits of the dc resistivity. The doping dependence of
these energies suggests that the orthorhombic, canted antiferromagnetic ground
state tends toward an insulator-metal transition that is not realized due to
the formation of the ferromagnetic insulating state near Mn(4+) concentration ~
0.13.Comment: PRB in press, 5 pages, 6 figure
Fingerprints of intrinsic phase separation: magnetically doped two-dimensional electron gas
In addition to Anderson and Mott localization, intrinsic phase separation has
long been advocated as the third fundamental mechanism controlling the
doping-driven metal-insulator transitions. In electronic system, where charge
neutrality precludes global phase separation, it may lead to various
inhomogeneous states and dramaticahttp://arxiv.org/submit/215787/metadata arXiv
Submission metadatally affect transport. Here we theoretically predict the
precise experimental signatures of such phase-separation-driven metal-insulator
transitions. We show that anomalous transport is expected in an intermediate
regime around the transition, displaying very strong temperature and magnetic
field dependence, but very weak density dependence. Our predictions find
striking agreement with recent experiments on Mn-doped CdTe quantum wells, a
system where we identify the microscopic origin for intrinsic phase separation.Comment: 4+epsilon pages, 4 figure
Towards first-principles understanding of the metal-insulator transition in fluid alkali metals
By treating the electron-ion interaction as perturbation in the
first-principles Hamiltonian, we have calculated the density response functions
of a fluid alkali metal to find an interesting charge instability due to
anomalous electronic density fluctuations occurring at some finite wave vector
{\bi Q} in a dilute fluid phase above the liquid-gas critical point. Since
|{\bi Q}| is smaller than the diameter of the Fermi surface, this instability
necessarily impedes the electric conduction, implying its close relevance to
the metal-insulator transition in fluid alkali metals.Comment: 11 pages, 5 figure
Nearly frozen Coulomb Liquids
We show that very long range repulsive interactions of a generalized
Coulomb-like form , with (-dimensionality),
typically introduce very strong frustration, resulting in extreme fragility of
the charge-ordered state. An \textquotedbl{}almost frozen\textquotedbl{} liquid
then survives in a broad dynamical range above the (very low) melting
temperature which is proportional to . This
\textquotedbl{}pseudogap\textquotedbl{} phase is characterized by unusual
insulating-like, but very weakly temperature dependent transport, similar to
experimental findings in certain low carrier density systems.Comment: 5 pages,4 figure
Colossal electroresistance in ferromagnetic insulating state of single crystal NdPbMnO
Colossal electroresistance (CER) has been observed in the ferromagnetic
insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs
in the absence of magnetoresistance (MR). Measurements of electroresistance
(ER) and current induced resistivity switching have been performed in the
ferromagnetic insulating state of a single crystal manganite of composition
NdPbMnO (NPMO30). The sample has a paramagnetic to
ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic
insulating state is realized for temperatures, T <~ 130 K. The colossal
electroresistance, arising from a strongly nonlinear dependence of resistivity
() on current density (j), attains a large value () in the
ferromagnetic insulating state. The severity of this nonlinear behavior of
resistivity at high current densities is progressively enhanced with decreasing
temperature, resulting ultimately, in a regime of negative differential
resistivity (NDR, d/dj < 0) for temperatures <~ 25 K. Concomitant with
the build-up of the ER however, is a collapse of the MR to a small value (<
20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms
that give rise to ER and MR are effectively decoupled in the ferromagnetic
insulating phase of manganites. We establish that, the behavior of
ferromagnetic insulating phase is distinct from the ferromagnetic metallic
(FMM) phase as well as the charge ordered insulating (COI) phase, which are the
two commonly realized ground state phases of manganites.Comment: 24 pages (RevTeX4 preprint), 8 figures, submitted to PR
Photon deflection by a Coulomb field in noncommutative QED
In noncommutative QED photons present self-interactions in the form of triple
and quartic interactions. The triple interaction implies that, even though the
photon is electrically neutral, it will deflect when in the presence of an
electromagnetic field. If detected, such deflection would be an undoubted
signal of noncommutative space-time. In this work we derive the general
expression for the deflection of a photon by any electromagnetic field. As an
application we consider the case of the deflection of a photon by an external
static Coulomb field.Comment: 07 pages, some typos corrected, accepted for publication in JP
Magnetoresistance scaling in the layered cobaltate Ca3Co4O9
We investigate the low temperature magnetic field dependences of both the
resistivity and the magnetization in the misfit cobaltate Ca3Co4O9 from 60 K
down to 2 K. The measured negative magnetoresistance reveals a scaling behavior
with the magnetization which demonstrates a spin dependent diffusion mechanism.
This scaling is also found to be consistent with a shadowed metalliclike
conduction over the whole temperature range. By explaining the observed
transport crossover, this result shed a new light on the nature of the
elementary excitations relevant to the transport
High electrical conductance enhancement in Au-nanoparticle decorated sparse single-wall carbon nanotube networks
The authors thank the Engineering and Physical Science
Research Council for funding through the Imperial College
London/Queen Mary Unive
Transport and Spectra in the Half-filled Hubbard Model: A Dynamical Mean Field Study
We study the issues of scaling and universality in spectral and transport
properties of the infinite dimensional particle--hole symmetric (half-filled)
Hubbard model within dynamical mean field theory. One of the simplest and
extensively used impurity solvers, namely the iterated perturbation theory
approach is reformulated to avoid problems such as analytic continuation of
Matsubara frequency quantities or calculating multi-dimensional integrals,
while taking full account of the very sharp structures in the Green's functions
that arise close to the Mott transitions and in the Mott insulator regime. We
demonstrate its viability for the half-filled Hubbard model. Previous known
results are reproduced within the present approach. The universal behavior of
the spectral functions in the Fermi liquid regime is emphasized, and adiabatic
continuity to the non-interacting limit is demonstrated. The dc resistivity in
the metallic regime is known to be a non-monotonic function of temperature with
a `coherence peak'. This feature is shown to be a universal feature occurring
at a temperature roughly equal to the low energy scale of the system. A
comparison to pressure dependent dc resistivity experiments on Selenium doped
NiS yields qualitatively good agreement. Resistivity hysteresis across the
Mott transition is shown to be described qualitatively within the present
framework. A direct comparison of the thermal hysteresis observed in VO
with our theoretical results yields a value of the hopping integral, which we
find to be in the range estimated through first-principle methods. Finally, a
systematic study of optical conductivity is carried out and the changes in
absorption as a result of varying interaction strength and temperature are
identified.Comment: 19 pages, 12 figure
Comment on: Weak Anisotropy and Disorder Dependence of the In-Plane Magnetoresistance in High-Mobility (100) Si Inversion Layers
Comment on: Weak Anisotropy and Disorder Dependence of the In-Plane
Magnetoresistance in High-Mobility (100) Si Inversion LayersComment: 1 page, submitted to PR
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