1,848 research outputs found
Electronic phase diagram of the layered cobalt oxide system, LixCoO2 (0.0 <= x <= 1.0)
Here we report the magnetic properties of the layered cobalt oxide system,
LixCoO2, in the whole range of Li composition, 0 <= x <= 1. Based on
dc-magnetic susceptibility data, combined with results of 59Co-NMR/NQR
observations, the electronic phase diagram of LixCoO2 has been established. As
in the related material NaxCoO2, a magnetic critical point is found to exist
between x = 0.35 and 0.40, which separates a Pauli-paramagnetic and a
Curie-Weiss metals. In the Pauli-paramagnetic regime (x <= 0.35), the
antiferromagnetic spin correlations systematically increase with decreasing x.
Nevertheless, CoO2, the x = 0 end member is a non-correlated metal in the whole
temperature range studied. In the Curie-Weiss regime (x >= 0.40), on the other
hand, various phase transitions are observed. For x = 0.40, a susceptibility
hump is seen at 30 K, suggesting the onset of static AF order. A magnetic jump,
which is likely to be triggered by charge ordering, is clearly observed at Tt =
175 K in samples with x = 0.50 (= 1/2) and 0.67 (= 2/3), while only a tiny kink
appears at T = 210 K in the sample with an intermediate Li composition, x =
0.60. Thus, the phase diagram of the LixCoO2 system is complex, and the
electronic properties are sensitively influenced by the Li content (x).Comment: 29 pages, 1 table, 9 figure
Impact of lithium composition on the thermoelectric properties of the layered cobalt oxide system LixCoO2
Thermoelectric properties of the layered cobalt oxide system LixCoO2 were
investigated in a wide range of Li composition, 0.98 >= x >= 0.35. Single-phase
bulk samples of LixCoO2 were successfully obtained through electrochemical
deintercalation of Li from the pristine LiCoO2 phase. While LixCoO2 with x >=
0.94 is semiconductive, the highly Li-deficient phase (0.75 >= x >= 0.35)
exhibits metallic conductivity. The magnitude of Seebeck coefficient at 293 K
(S293K) significantly depends on the Li content (x). The S293K value is as
large as +70 ~ +100 uV/K for x >= 0.94, and it rapidly decreases from +90 uV/K
to +10 uV/K as x is lowered within a Li composition range of 0.75 >= x >= 0.50.
This behavior is in sharp contrast to the results of x <= 0.40 for which the
S293K value is small and independent of x (+10 uV/K), indicating that a
discontinuous change in the thermoelectric characteristics takes place at x =
0.40 ~ 0.50. The unusually large Seebeck coefficient and metallic conductivity
are found to coexist in a narrow range of Li composition at about x = 0.75. The
coexistence, which leads to an enhanced thermoelectric power factor, may be
attributed to unusual electronic structure of the two-dimensional CoO2 block.Comment: 29 pages, 1 table, 8 figure
Reheating after f(R) inflation
The reheating dynamics after the inflation induced by -corrected
model is considered. To avoid the complexity of solving the fourth order
equations, we analyze the inflationary and reheating dynamics in the Einstein
frame and its analytical solutions are derived. We also perform numerical
calculation including the backreaction from the particle creation and compare
the results with the analytical solutions. Based on the results, observational
constraints on the model are discussed.Comment: 16 pages, 11 figure
Measurement of electron correlations in LixCoO2 (x=0.0 - 0.35) using 59Co nuclear magnetic resonance and nuclear quadrupole resonance techniques
CoO2 is the parent compound for the superconductor NaxCoO2\cdot1.3H2O and was
widely believed to be a Mott insulator. We performed 59Co nuclear magnetic
resonance (NMR) and nuclear quadrupole resonance (NQR) studies on LixCoO2 (x =
0.35, 0.25, 0.12, and 0.0) to uncover the electronic state and spin
correlations in this series of compounds which was recently obtained through
electrochemical de-intercalation of Li from pristine LiCoO2. We find that
although the antiferromagnetic spin correlations systematically increase with
decreasing Li-content (x), the end member, CoO2 is a non-correlated metal that
well satisfies the Korringa relation for a Fermi liquid. Thus, CoO2 is not
simply located at the limit of x->0 for AxCoO2 (A = Li, Na) compounds. The
disappearance of the electron correlations in CoO2 is due to the three
dimensionality of the compound which is in contrast to the highly two
dimensional structure of AxCoO2.Comment: 4pages, 4figures, to be published in Phys.Rev.B. Rapid
Bulk antiferromagnetism in single crystals
Susceptibility, specific heat, and muon spin rotation measurements on
high-quality single crystals of have revealed bulk
antiferromagnetism with N\'{e}el temperature K and an
ordered moment perpendicular to the layers. The magnetic order
encompasses nearly 100% of the crystal volume. The susceptibility exhibits a
broad peak around 30 K, characteristic of two-dimensional antiferromagnetic
fluctuations. The in-plane resistivity is metallic at high temperatures and
exhibits a minimum at .Comment: published versio
New Josephson Plasma Modes in Underdoped YBa2Cu3O6.6 Induced by Parallel Magnetic Field
The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured
below Tc=59K in parallel magnetic fields H//CuO2 up to 7T. Upon application of
a parallel field, a new peak appears at finite frequency in the optical
conductivity at the expense of suppression of c-axis condensate weight. We
conclude that the dramatic change originates from different Josephson coupling
strengths between bilayers with and without Josephson vortices. We find that
the 400cm^-1 broad conductivity peak in YBCO gains the spectral weight under
parallel magnetic field; this indicates that the condensate weight at \omega =0
is distributed to the intra-bilayer mode as well as to the new optical
Josephson mode.Comment: 4 pages, 3 figure
Plasma Atomic Processes Explored by Optical Emission Spectroscopy of Excited Atoms Sputtered from the Metal Surface by Ion Bombardment
Future cosmological evolution in gravity using two equations of state parameters
We investigate the issues of future oscillations around the phantom divide
for gravity. For this purpose, we introduce two types of energy density
and pressure arisen from the -higher order curvature terms. One has the
conventional energy density and pressure even in the beginning of the Jordan
frame, whose continuity equation provides the native equation of state . On the other hand, the other has the different forms of energy density
and pressure which do not obviously satisfy the continuity equation. This needs
to introduce the effective equation of state to describe the
-fluid, in addition to the native equation of state .
We confirm that future oscillations around the phantom divide occur in
gravities by introducing two types of equations of state. Finally, we point out
that the singularity appears ar because the stability condition of
gravity violates.Comment: 23 pages, 10 figures, correcting typing mistake in titl
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