3,323 research outputs found
Search for Scaling Dimensions for Random Surfaces with c=1
We study numerically the fractal structure of the intrinsic geometry of
random surfaces coupled to matter fields with . Using baby universe
surgery it was possible to simulate randomly triangulated surfaces made of
260.000 triangles. Our results are consistent with the theoretical prediction
for the intrinsic Hausdorff dimension.Comment: 10 pages, (csh will uudecode and uncompress ps-file), NBI-HE-94-3
Physical properties of Ce3-xTe4 below room temperature
The physical properties of polycrystalline Ce3-xTe4 were investigated by
measurements of the thermoelectric properties, Hall coefficient, heat capacity,
and magnetization. The fully-filled, metallic x=0 compound displays a soft
ferromagnetic transition near 4K, and analysis of the corresponding heat
capacity anomaly suggests a doublet ground state for Ce^{3+}. The transition is
suppressed to below 2K in the insulating x=0.33 composition, revealing that
magnetic order in Ce3-xTe4 is driven by an RKKY-type interaction. The
thermoelectric properties trend with composition as expected from simple
electron counting, and the transport properties in Ce3Te4 are observed to be
similar to those in La3Te4. Trends in the low temperature thermal conductivity
data reveal that the phonons are efficiently scattered by electrons, while all
compositions examined have a lattice thermal conductivity near 1.2W/m/K at
200K.Comment: Submitted to Phys. Rev.
Magnetic field effect on Fe-induced short-range magnetic correlation and electrical conductivity in BiPbSrCuFeO
We report electrical resistivity measurements and neutron diffraction studies
under magnetic fields of
BiPbSrCuFeO, in which hole
carriers are overdoped. This compound shows short-range incommensurate magnetic
correlation with incommensurability , whereas a Fe-free compound
shows no magnetic correlation. Resistivity shows an up turn at low temperature
in the form of and shows no superconductivity. We observe reduction
of resistivity by applying magnetic fields (i.e., a negative magnetoresistive
effect) at temperatures below the onset of short-range magnetic correlation.
Application of magnetic fields also suppresses the Fe induced incommensurate
magnetic correlation. We compare and contrast these observations with two
different models: 1) stripe order, and 2) dilute magnetic moments in a metallic
alloy, with associated Kondo behavior. The latter picture appears to be more
relevant to the present results.Comment: 7 pages, 5 figure
Pairs of Noncrossing Free Dyck Paths and Noncrossing Partitions
Using the bijection between partitions and vacillating tableaux, we establish
a correspondence between pairs of noncrossing free Dyck paths of length
and noncrossing partitions of with blocks. In terms of the
number of up steps at odd positions, we find a characterization of Dyck paths
constructed from pairs of noncrossing free Dyck paths by using the Labelle
merging algorithm.Comment: 9 pages, 5 figures, revised version, to appear in Discrete
Mathematic
Structural phase transition and dielectric relaxation in Pb(Zn1/3Nb2/3)O3 single crystals
The structure and the dielectric properties of Pb(Zn1/3Nb2/3)O3 (PZN) crystal
have been investigated by means of high-resolution synchrotron x-ray
diffraction (with an x-ray energy of 32 keV) and dielectric spectroscopy (in
the frequency range of 100 Hz - 1 MHz). At high temperatures, the PZN crystal
exhibits a cubic symmetry and polar nanoregions inherent to relaxor
ferroelectrics are present, as evidenced by the single (222) Bragg peak and by
the noticeable tails at the basis of the peak. At low temperatures, in addition
to the well-known rhombohedral phase, another low-symmetry, probably
ferroelectric, phase is found. The two phases coexist in the form of mesoscopic
domains. The para- to ferroelectric phase transition is diffused and observed
between 325 and 390 K, where the concentration of the low-temperature phases
gradually increases and the cubic phase disappears upon cooling. However, no
dielectric anomalies can be detected in the temperature range of diffuse phase
transition. The temperature dependence of the dielectric constant show the
maximum at higher temperature (Tm = 417 - 429 K, depending on frequency) with
the typical relaxor dispersion at T < Tm and the frequency dependence of Tm
fitted to the Vogel-Fulcher relation. Application of an electric field upon
cooling from the cubic phase or poling the crystal in the ferroelectric phase
gives rise to a sharp anomaly of the dielectric constant at T 390 K and
diminishes greatly the dispersion at lower temperatures, but the dielectric
relaxation process around Tm remains qualitatively unchanged. The results are
discussed in the framework of the present models of relaxors and in comparison
with the prototypical relaxor ferroelectric Pb(Mg1/3Nb2/3)O3.Comment: PDF file, 13 pages, 6 figures collected on pp.12-1
The ground state of a quantum critical system
The competition between the tendency of magnetic moments to order at low temperatures, and the tendency of conduction electrons to shield these moments, can result in a phase transition that takes place at zero Kelvin, the quantum critical point (QCP). So far, the ground state of these types of systems has remained unresolved. We present neutron scattering experiments that show that the ground state of a sample representative of a class of QCP-systems is determined by the residual interactions between the conduction electrons, resulting in a state with incommensurate intermediate-range order. However, long-range order is thwarted by quantum fluctuations that locally destroy magnetic moments, leaving the system with too few moments to achieve long-range order
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