986 research outputs found
Transport and magnetic properties in YBaCo2O5.45: Focus on the high-temperature transition
The electronic transport properties and the magnetic susceptibility were
measured in detail in . Close to the so-called metal-insulator
transition, strong effects of resistance relaxation, a clear thermal hysteresis
and a sudden increase of the resistance noise are observed. This is likely due
to the first order character of the transition and to the underlying phases
coexistence. Despite these out of equilibrium features, a positive and linear
magneto-resistance is also observed, possibly linked to the heterogeneity of
the state. From a magnetic point of view, the paramagnetic to ordered magnetic
state transition is observed using non linear susceptibilty. This transition
shows the characteristics of a continuous transition, and time dependent
effects can be linked with the dynamics of magnetic domains in presence of
disorder. Thus, when focusing on the order of the transitions, the electronic
one and the magnetic one can not be directly associated.Comment: accepted for publication in PR
Thermal phase diagrams of columnar liquid crystals
In order to understand the possible sequence of transitions from the
disordered columnar phase to the helical phase in hexa(hexylthio)triphenylene
(HHTT), we study a three-dimensional planar model with octupolar interactions
inscribed on a triangular lattice of columns. We obtain thermal phase diagrams
using a mean-field approximation and Monte Carlo simulations. These two
approaches give similar results, namely, in the quasi one-dimensional regime,
as the temperature is lowered, the columns order with a linear polarization,
whereas helical phases develop at lower temperatures. The helicity patterns of
the helical phases are determined by the exact nature of the frustration in the
system, itself related to the octupolar nature of the molecules.Comment: 12 pages, 9 figures, ReVTe
Rhodium Doped Manganites : Ferromagnetism and Metallicity
The possibility to induce ferromagnetism and insulator to metal transitions
in small A site cation manganites Ln_{1-x}Ca_xMnO_3 by rhodium doping is shown
for the first time. Colossal magnetoresistance (CMR) properties are evidenced
for a large compositional range (0.35 \leq x < 0.60). The ability of rhodium to
induce such properties is compared to the results obtained by chromium and
ruthenium doping. Models are proposed to explain this behavior.Comment: 11 pages, 8 figure
Cathodoluminescence in a (S)TEM - Exploring Possibilities and Limits
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 - August 5, 201
Monte Carlo Simulations of an Extended Feynman-Kikuchi Model
We present Quantum Monte Carlo simulations of a generalization of the
Feynman-Kikuchi model which includes the possibility of vacancies and
interactions between the particles undergoing exchange. By measuring the
winding number (superfluid density) and density structure factor, we determine
the phase diagram, and show that it exhibits regions which possess both
superfluid and charge ordering.Comment: 10 pages, 15 figure
Strongly correlated properties of the thermoelectric cobalt oxide Ca3Co4O9
We have performed both in-plane resistivity, Hall effect and specific heat
measurements on the thermoelectric cobalt oxide CaCoO. Four
distinct transport regimes are found as a function of temperature,
corresponding to a low temperature insulating one up to 63 K,
a strongly correlated Fermi liquid up to 140 K, with
and , followed
by an incoherent metal with and a high temperature insulator above
T510 K . Specific heat Sommerfeld coefficient
mJ/(mol.K) confirms a rather large value of the electronic effective mass
and fulfils the Kadowaki-Woods ratio 10 . Resistivity measurements under pressure reveal a
decrease of the Fermi liquid transport coefficient A with an increase of
as a function of pressure while the product remains constant and
of order . Both thermodynamic and transport properties suggest a strong
renormalization of the quasiparticles coherence scale of order that seems
to govern also thermopower.Comment: 5 pages, 6 figures, accepted for publication in Physical Review
Borel-Moore motivic homology and weight structure on mixed motives
By defining and studying functorial properties of the Borel-Moore motivic
homology, we identify the heart of Bondarko-H\'ebert's weight structure on
Beilinson motives with Corti-Hanamura's category of Chow motives over a base,
therefore answering a question of Bondarko
Filling-induced Mott transition and pseudogap physics in the triangular lattice Hubbard model
It has been reported that upon doping a Mott insulator, there can be a
crossover to a strongly correlated metallic phase followed by a first-order
transition to another thermodynamically stable metallic phase. We call this
first-order metal-metal transition the Sordi transition. To show theoretically
that this transition is observable, it is important to provide calculations in
situations where magnetic phase transitions do not hide the Sordi transition.
It is also important to show that it can be found on large clusters and with
different approaches. Here, we use the dynamical cluster approximation to
reveal the Sordi transition on a triangular lattice at finite temperature in
situations where there is no long-range magnetic correlations. This is relevant
for experiments on candidate spin-liquid organics. We also show that the
metallic phase closest to the insulator is a distinct pseudogap phase that
occurs because of strong interactions and short-range correlations
New electronic orderings observed in cobaltates under the influence of misfit periodicities
We study with ARPES the electronic structure of CoO2 slabs, stacked with
rock-salt (RS) layers exhibiting a different (misfit) periodicity. Fermi
Surfaces (FS) in phases with different doping and/or periodicities reveal the
influence of the RS potential on the electronic structure. We show that these
RS potentials are well ordered, even in incommensurate phases, where STM images
reveal broad stripes with width as large as 80\AA. The anomalous evolution of
the FS area at low dopings is consistent with the localization of a fraction of
the electrons. We propose that this is a new form of electronic ordering,
induced by the potential of the stacked layers (RS or Na in NaxCoO2) when the
FS becomes smaller than the Brillouin Zone of the stacked structure
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