236 research outputs found

### Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3

The dielectric constant of the incipient ferroelectric EuTiO$_3$ exhibits a
sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering
of the Eu spins simultaneously appears, indicating coupling between the
magnetism and dielectric properties. This may be attributed to the modification
of the soft-phonon mode, $T_{1\mu}$, which is the main contribution to the
large dielectric constant, by the Eu spins(7$\mu_B$ per Eu). By adding the
coupling term between the magnetic and electrical subsystems as $-g\sum\limits_l {\sum\limits_{< {i,j}} {q_l^2}} \overrightarrow {S_i} \cdot
\overrightarrow {S_j}$ we show that the variation of the frequency of
soft-phonon mode depends on the spin correlation between the nearest neighbors
Eu spins and is substantially changed under a magnetic field.Comment: 13 pages, 4 figure

### Ordering Process and Its Hole Concentration Dependence of the Stripe Order in La{2-x}Sr{x}NiO{4}

Ordering process of stripe order in La{2-x}Sr{x}NiO{4} with x being around
1/3 was investigated by neutron diffraction experiments. When the stripe order
is formed at high temperature, incommensurability \epsilon of the stripe order
has a tendency to show the value close to 1/3 for the samples with x at both
sides of 1/3. With decreasing temperature, however, \epsilon becomes close to
the value determined by the linear relation of \epsilon = n_h, where n_h is a
hole concentration. This variation of the \epsilon strongly affects the
character of the stripe order through the change of the carrier densities in
stripes and antiferromagnetic domains.Comment: 5 pages, 3 figures, REVTeX, to be published in Phys. Rev.

### Photoemission Spectral Weight Transfer and Mass Renormalization in the Fermi-Liquid System La$_{1-x}$Sr$_x$TiO$_{3+y/2}$

We have performed a photoemission study of La$_{1-x}$Sr$_x$TiO$_{3+y/2}$ near
the filling-control metal-insulator transition (MIT) as a function of hole
doping. Mass renormalization deduced from the spectral weight and the width of
the quasi-particle band around the chemical potential $\mu$ is compared with
that deduced from the electronic specific heat. The result implies that, near
the MIT, band narrowing occurs strongly in the vicinity of $\mu$. Spectral
weight transfer occurs from the coherent to the incoherent parts upon
antiferromagnetic ordering, which we associate with the partial gap opening at
$\mu$.Comment: 4 pages, 3 figure

### Universal charge transport of the Mn oxides in the high temperature limit

We have found that various Mn oxides have the universal resistivity and
thermopower in the high temperature limit. The resistivities and thermopowers
of all the samples go toward constant values of 7$\pm$1 m$\Omega$cm and
$-79\pm$3 $\mu$V/K, which are independent of carrier density and crystal
structures. We propose that the electric conduction occurs in a highly
localized way in the high temperature limit, where the exchange of entropy and
charge occurs in the neighboring Mn$^{3+}$ and Mn$^{4+}$ ions.Comment: 4 pages, 4 eps figures, to be published in J. Appl. Phy

### Charge ordering and chemical potential shift in La$_{2-x}$Sr$_x$NiO$_4$ studied by photoemission spectroscopy

We have studied the chemical potential shift in La$_{2-x}$Sr$_x$NiO$_4$ and
the charge ordering transition in La$_{1.67}$Sr$_{0.33}$NiO$_4$ by
photoemission spectroscopy. The result shows a large ($\sim$ 1 eV/hole)
downward shift of the chemical potential with hole doping in the high-doping
regime ($\delta \gtrsim$ 0.33) while the shift is suppressed in the low-doping
regime ($\delta \lesssim$ 0.33). This suppression is attributed to a
segregation of doped holes on a microscopic scale when the hole concentration
is lower than $\delta \simeq 1/3$. In the $\delta = 1/3$ sample, the
photoemission intensity at the chemical potential vanishes below the charge
ordering transition temperature $T_{\rm CO}=$ 240 K.Comment: 5 pages, 4 figure

### Unconventional spin fluctuations in the hexagonal antiferromagnet YMnO$_3$

We used inelastic neutron scattering to show that well below its N\'{e}el
temperature, $T_{\rm N}$, the two-dimensional (2D) XY nearly-triangular
antiferromagnet YMnO$_{3}$ has a prominent {\it central peak} associated with
2D antiferromagnetic fluctuations with a characteristic life time of 0.55(5)
ps, coexisting with the conventional long-lived spin-waves. Existence of the
two time scales suggests competition between the N\'{e}el phase favored by weak
interplane interactions, and the Kosterlitz-Thouless phase intrinsic to the 2D
XY spin system.Comment: 4pages, 5figure

### Electronic Structure of Charge- and Spin-controlled Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3}

We present the electronic structure of
Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3} investigated by high-resolution
photoemission spectroscopy. In the vicinity of Fermi level, it was found that
the electronic structure were composed of a Cr 3d local state with the
t_{2g}^{3} configuration and a Ti 3d itinerant state. The energy levels of
these Cr and Ti 3d states are well interpreted by the difference of the
charge-transfer energy of both ions. The spectral weight of the Cr 3d state is
completely proportional to the spin concentration x irrespective of the carrier
concentration y, indicating that the spin density can be controlled by x as
desired. In contrast, the spectral weight of the Ti 3d state is not
proportional to y, depending on the amount of Cr doping.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. Let

### Stripe order at low temperatures in La{2-x}Sr{x}NiO4 for 1/3 < x < 1/2

Stripe order in La{2-x}Sr{x}NiO4 beyond x = 1/3 was studied with neutron
scattering technique. At low temperatures, all the samples exhibit hole stripe
order. Incommensurability \epsilon of the stripe order is approximately linear
in the hole concentration n_h = x + 2\delta up to x = 1/2, where \delta denotes
the off-stoichiometry of oxygen atoms. The charge and spin ordering
temperatures exhibit maxima at n_h = 1/3, and both decrease beyond n_h > 1/3.
For 1/3 < n_h < 1/2, the stripe ordering consists of the mixture of the
\epsilon = 1/3 stripe order and the n_h = 1/2 charge/spin order.Comment: REVTeX, 4 pages, 4 figure

### Charge dynamics of Ca_{2-x}Na_{x}CuO_{2}Cl_{2} as a correlated electron system with the ideal tetragonal lattice

We report the reflectivity and the resistivity measurement of
Ca_{2-x}Na_{x}CuO_{2}Cl_{2} (CNCOC), which has a single-CuO2-plane lattice with
no orthorhombic distortion. The doping dependence of the in-plane optical
conductivity spectra for CNCOC is qualitatively the same to those of other
cuprates, but a slight difference between CNCOC and LSCO, i.e., the absence of
the 1.5 eV peak in CNCOC, can be attributed to the smaller charge-stripe
instability in CNCOC. The temperature dependence of the optical onductivity
spectra of CNCOC has been analyzed both by the two-component model
(Drude+Lorentzian) and by the one-component model (extended-Drude analysis).
The latter analysis gives a universal trend of the scattering rate Gamma(omega)
with doping. It was also found that Gamma(omega) shows a saturation behavior at
high frequencies, whose origin is the same as that of resistivity saturation at
high temperatures.Comment: 8 pages, 11 figures, to be published in Phys. Rev.

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