Metallic stripe in two dimensions: stability and spin-charge separation

The problems of charge stripe formation, spin-charge separation, and stability of the antiphase domain wall (ADW) associated with a stripe are addressed using an analytical approach to the t- J(z) model. We show that a metallic stripe together with its ADW is the ground state of the problem in the low doping regime. The stripe is described as a system of spinons and magnetically confined holons strongly coupled to the two dimensional spin environment with holon-spin-polaron elementary excitations filling a one-dimensional band.     

Measurement of structure-dependent K+ --> &mgr;(+)nu(&mgr;)gamma decay

We report the first measurement of a structure-dependent component in the decay K+-->&mgr;(+)nu(&mgr;)gamma. Using the kinematic region where the muon kinetic energy is greater than 137 MeV and the photon energy is greater than 90 MeV, we find that the absolute value of the sum of the vector and axial-vector form factors is |F(V)+F(A)| = 0.165+/-0.007+/-0.011. This corresponds to a branching ratio of B(SD+) = (1.33+/-0.12+/-0.18)x10(-5). We also set the limit -0. 04相似文献   

Evidence for gapped spin-wave excitations in the frustrated Gd2Sn2O7 pyrochlore antiferromagnet from low-temperature specific heat measurements

We have measured the low-temperature specific heat of the geometrically frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic field. The specific heat is found to drop exponentially below approximately 350 mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy resulting from single-ion effects and long-range dipolar interactions. The data are well fitted by linear spin-wave theory, ruling out unconventional low-energy magnetic excitations in this system, and allowing a determination of the pertinent exchange interactions in this material.     

Entropy and Ergodicity of Boole-Type Transformations

We review some analytic, measure-theoretic and topological techniques for studying ergodicity and entropy of discrete dynamical systems, with a focus on Boole-type transformations and their generalizations. In particular, we present a new proof of the ergodicity of the 1-dimensional Boole map and prove that a certain 2-dimensional generalization is also ergodic. Moreover, we compute and demonstrate the equivalence of metric and topological entropies of the 1-dimensional Boole map employing “compactified”representations and well-known formulas. Several examples are included to illustrate the results. We also introduce new multidimensional Boole-type transformations invariant with respect to higher dimensional Lebesgue measures and investigate their ergodicity and metric and topological entropies.     

Evolution of thermodynamic potentials in closed and open nanocrystalline systems: Ge-Si:Si(001) islands

An open (closed) system, in which matter is (not) exchanged through surface diffusion, was realized via growth kinetics. Epitaxially grown Si-Ge:Si (001) islands were annealed in different environments affecting the diffusivity of Si adatoms selectively. The evolution of the driving forces for intermixing while approaching the equilibrium was inferred from Synchrotron x-ray measurements of composition and strain. For the open system, intermixing due to the Si inflow from the wetting layer (reservoir) caused a decrease in the Ge content, leading to a lowering of the elastic energy and an increase in the mixing entropy. In contrast, for the closed system, while keeping the average Ge composition constant, atom rearrangement within the islands led to an increase in both elastic and entropic contributions. The Gibbs free energy decreased in both cases, despite the different evolution paths for the composition profiles.     

Further search for the decay K+-->pi(+)nunu;

A search for additional evidence for the rare kaon decay K+-->pi(+)nunu; has been made with a new data set comparable in sensitivity to the previous exposure that produced a single event. No new events were found in the pion momentum region examined, 211pi(+)nunu;) = 1.5(+3.4)(-1.2)x10(-10).     

Total cross sections of π, K, p and on protons and deuterons between 200 and 370 GeV/c

Total cross sections of π^±, K^±, p and on protons and deuterons have been measured at 6 momenta between 200 and 370 GeV/c.     

Magnetic ordering below 10K in the high-Tc superconductor YBa2(Cu0.985Fe0.015)3O7−σ

The high-temperature superconductor with the nominal composition YBa₂Cu₃O_7?σ has been doped with iron 93% enriched in⁵⁷Fe. When 1.5 at % Fe substitutes for Cu, the transition temperature is reduced by about 30° K with full ac shielding (X′=?1/4π) achieved by ≈40 K. At room temperature the Mössbauer spectrum consists of three overlapping doublets. Below 10 K, hyperfine-field splitting is observed; relaxation still takes place at T=1.8 K.