The fast CI method for second-order properties

Second-order properties are computed by diagonalizing a perturbed hamiltonian in a linear space L of low dimensionality. The choice of the basis vectors generating L is suggested by perturbation theory and previous work on correlation energy. Diagrammatic techniques can be used to compute the relevant matrix elements. Test numerical computations performed on the hydrogen molecule gave satisfactory results for the dipole polarizability and nuclear spin-spin coupling constant.     

Electric-pulse-induced local conducting area and joule heating effect in VO2/Al2O3 films

We investigated the effect of an electric-pulse on the insulator–metal phase transition of VO₂/Al₂O₃ films using synchrotron-based infrared microspectroscopy. By monitoring the time-resolved optical response, we could demonstrate that local conducting areas are formed under the influence of the electric-pulse, and the Joule heat generated from the local current flow drives a consecutive thermal phase transition in the adjacent sample area.     

Phase diagram of La2-xSrxCuO4 probed in the infared: imprints of charge stripe excitations

While there is increasing evidence for antiferromagnetic (AF) ordering in the Cu-O planes of high-T(c) superconductors, either static or fluctuating, there is no direct evidence so far for the charge stripes that should separate the AF domains. By investigating the optical response of La2-xSrxCuO4 for 0相似文献   

On $\mathsf{c = 1}$ critical phases in anisotropic spin-1 chains

Quantum spin-1 chains may develop massless phases in presence of Ising-like and single-ion anisotropies. We have studied c = 1 critical phases by means of both analytical techniques, including a mapping of the lattice Hamiltonian onto an O(2) NL M, and a multi-target DMRG algorithm which allows for accurate calculation of excited states. We find excellent quantitative agreement with the theoretical predictions and conclude that a pure Gaussian model, without any orbifold construction, describes correctly the low-energy physics of these critical phases. This combined analysis indicates that the multicritical point at large single-ion anisotropy does not belong to the same universality class as the Takhtajan-Babujian Hamiltonian as claimed in the past. A link between string-order correlation functions and twisting vertex operators, along the c = 1 line that ends at this point, is also suggested.Received: 16 July 2003, Published online: 24 October 2003PACS: 75.40.-s Critical-point effects, specific heats, short-range order - 75.10.Jm Quantized spin models - 02.70.-c Computational techniques     

Quasi-single-helicity reversed-field-pinch plasmas

The reversed field pinch (RFP) is a configuration for plasma magnetic confinement. It has been traditionally viewed as dominated by a bath of MHD instabilities producing magnetic chaos and high energy transport. We report experimental results which go beyond this view. They show a decrease of magnetic chaos and the formation of a coherent helical structure in the plasma, whose imaging and temperature profile are provided for the first time. These quasi-single-helicity states are observed both transiently and in stationary conditions. The last case is consistent with a theoretically predicted bifurcation. Our results set a new frame for improving confinement in high current nonchaotic RFP's.     

Substrateless micrometric metal mesh for mid-infrared plasmonic sensors

We report on the fabrication and optical properties of thin metal films periodically patterned with square hole arrays of 2 micron pitch, which behave as substrateless plasmonic devices at mid-infrared frequencies. Large (3×3 mm²) meshes were fabricated by metallizing a patterned silicon nitride membrane. The mid-infrared spectra display resonant absorption lines with a Q-factor up to 22 in both transmission and reflection, due to the interaction of the radiation with surface plasmon modes on both faces of the film, allowed by substrate removal. The devices can be used to fabricate surface plasmon-based chemical sensors employing mid-infrared radiation.     

Incommmensurability and unconventional superconductor to insulator transition in the hubbard model with bond-charge interaction

We determine the quantum phase diagram of the one-dimensional Hubbard model with bond-charge interaction X in addition to the usual Coulomb repulsion U>0 at half-filling. For large enough X相似文献   

Graphene solutions

Thermodynamics drive the spontaneous dissolution of a graphite intercalation compound (GIC) KC(8) in NMP to form stable solutions. Reduction potential of graphene is measured at +22 mV vs. SCE. Single layer graphene flakes (ca. 1 μm(2)) have been unambiguously identified by electron diffraction.