15 research outputs found
Visualizing high-temperature spin dynamics in La1-xCaxMnO3 from a mapping of EPR linewidth and g factor
This paper presents an analysis of electron paramagnetic resonance
parameters, i.e., g factor, linewidth, and intensity on powder samples of
La1-xCaxMnO3 at the commensurate carrier concentrations of x = N/8 (N = 1, 2,
3, 4, 5, 6, and 7). We demonstrate that the mapping of EPR parameters offers a
powerful tool to investigate high-temperature spin dynamics in the phase
diagram of colossal magnetoresistance (CMR) manganites. Our results convince
that the spin-spin relaxation mechanism should dominate the high-temperature
paramagnetic regime in CMR manganites.Comment: 19 pages, 6 figure
Colossal Magnetoresistant Materials: The Key Role of Phase Separation
The study of the manganese oxides, widely known as manganites, that exhibit
the ``Colossal'' Magnetoresistance (CMR) effect is among the main areas of
research within the area of Strongly Correlated Electrons. After considerable
theoretical effort in recent years, mainly guided by computational and
mean-field studies of realistic models, considerable progress has been achieved
in understanding the curious properties of these compounds. These recent
studies suggest that the ground states of manganite models tend to be
intrinsically inhomogeneous due to the presence of strong tendencies toward
phase separation, typically involving ferromagnetic metallic and
antiferromagnetic charge and orbital ordered insulating domains. Calculations
of the resistivity versus temperature using mixed states lead to a good
agreement with experiments. The mixed-phase tendencies have two origins: (i)
electronic phase separation between phases with different densities that lead
to nanometer scale coexisting clusters, and (ii) disorder-induced phase
separation with percolative characteristics between equal-density phases,
driven by disorder near first-order metal-insulator transitions. The coexisting
clusters in the latter can be as large as a micrometer in size. It is argued
that a large variety of experiments reviewed in detail here contain results
compatible with the theoretical predictions. It is concluded that manganites
reveal such a wide variety of interesting physical phenomena that their
detailed study is quite important for progress in the field of Correlated
Electrons.Comment: 76 pages, 21 PNG files with figures. To appear in Physics Report
Azimuthal anisotropy and correlations in the hard scattering regime at RHIC
Azimuthal anisotropy (v(2)) and two-particle angular correlations of high p(T) charged hadrons have been measured in Au+Au collisions at roots(NN) = 130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high p(T) partons. The monotonic rise of v(2)(p(T)) for p(T) 3 GeV/c, a saturation of v(2) is observed which persists up to p(T) = 6 GeV/c
Disappearance of back-to-back high-p(T) hadron correlations in central Au+Au collisions at root s(NN)=200 GeV
Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in Au+Au and p+p collisions at roots(NN)=200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for p+p and peripheral Au+Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium
Coherent rho(0) production in ultraperipheral heavy-ion collisions
The STAR Collaboration reports the first observation of exclusive rho(0) photoproduction, AuAu-->AuAurho(0), and rho(0) production accompanied by mutual nuclear Coulomb excitation, AuAu-->Au(star)Au(star)rho(0), in ultraperipheral heavy-ion collisions. The rho(0) have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at s(NN)=130 GeV agree with theoretical predictions treating rho(0) production and Coulomb excitation as independent processes
Azimuthal anisotropy of K-S(0) and Lambda+(Lambda)over-bar production at midrapidity from Au plus Au collisions at root s(NN)=130 GeV
We report STAR results on the azimuthal anisotropy parameter v(2) for strange particles K-S(0), Lambda, and (&ULambda;) over bar at midrapidity in Au+Au collisions at roots(NN)=130 GeV at the Relativistic Heavy Ion Collider. The value of v(2) as a function of transverse momentum, p(t), of the produced particle and collision centrality is presented for both particles up to p(t)similar to3.0 GeV/c. A strong p(t) dependence in v(2) is observed up to 2.0 GeV/c. The v(2) measurement is compared with hydrodynamic model calculations. The physics implications of the p(t) integrated v(2) magnitude as a function of particle mass are also discussed
d̅ and 3He̅ Production in √sNN = 130 GeV Au+Au Collisions
A report on the first measurements of light antinucleus production in Au + Au collisions at the Relativistic Heavy-Ion Collider (RHIC) was presented. The production rates for d̄ and He were observed to be much larger than in lower energy nucleus-nucleus collisions. A little or no increase in the antinucleon freeze-out volume compared to CERN Super Proton Synchrotron (SPS) energy was indicated by a coalescence model analysis. The He freeze-out volume was indicated to be smaller than the d̄ freeze-out volume