Electrical resistivity in the strong-correlation limit of the emery model

On the basis of the Emery model in the limitU _d , the electrical resistivity is calculated by means of the memory function method. The inelastic scattering of oxygen holes on transverse and longitudinal antiferromagnetic spin fluctuations of copper spins is considered. Assuming a Fermi-liquid model for the dynamic spin susceptibility, the two-dimensional spin-fluctuation resistivity reveals a crossover from a quadratic to a linear temperature dependence. This may explain the normal-state basal-plane resistivity of high-T _c superconductors, in particular the observed non-linear temperature dependences.     

Stability of impulsively-driven natural convection with unsteady base state: implications of an adiabatic boundary

Stability conditions of a quiescent, horizontally infinite fluid layer with adiabatic bottom subject to sudden cooling from above are studied. Here, at difference from Rayleigh-Bénard convection, the temperature base state is never steady. Instability limits are studied using linear analysis while stability is analyzed using the energy method. Critical stability curves in terms of Rayleigh numbers and convection onset times were obtained for several kinematic boundary conditions. Stability curves resulting from energy and linear approaches exhibit the same temporal growth rate for large values of time, suggesting a bound for the temporal asymptotic behavior of the energy method.     

Dynamic spin and charge susceptibilities in thet−J model

Based on the spin-rotation-invariant formulation of the Kotliar Ruckenstein slave-boson representation, the paramagnetic spin and charge susceptibilities in thet-J model are calculated. Analyzing the static spin susceptibility, the instability of the paraphase towards incommensurate magnetic order is in agreement, with the saddle-point phase diagram recently obtained by some of the authors. The spin dynamics at arbitrary frequencies, wave vectors and band fillings is calculated, where the Fermi-surface and correlation effects are studied. The magnetic instability region is investigated with respect to the formation of a collective spin-fluctuation mode. Near the transition point, a kinetic gap and a sharp peak in the spectral weight ((1,0) paramagnon) are obtained.     

Optical and dc conductivities in high-T c superconductors: Spin-fluctuation scattering in the Emery model

On the basis of the Emery model for the CuO₂ plane, the optical conductivity and resistivity due to the inelastic scattering of oxygen holes by antiferromagnetic fluctuations of copper spins are calculated. For moderate hole doping, the electrical conductivity obeys a generalized Drude law. Using a phenomenological model for the dynamic spin susceptibility, the in-plane resistivity reveals a crossover from a quadratic to a linear temperature dependence at the scale of the spin-fluctuation energy. The frequency dependence of the scattering rate changes from a quadratic to a linear increase over a wide frequency range. The theory is compared with experiments on LSCO and YBCO compounds, where the spin dynamics is described within the model by Millis et al. A good quantitative agreement (in particular of the frequency-dependent scattering rate) with experiments is found. We conclude that the spin-fluctuation scattering may play a dominant role in the transport properties of Cu-oxide superconductors.     

Protonium annihilation in optical models

We calculate the wave-functions, energy shifts and widths of low lying protonium states using different optical potentials (Dover-Richard, Kohno-Weise). The importance of tensor and isospin coupling is studied and the initial state distortion is compared for protonium annihilation andp¯p annihilation in flight at low energy. We study the range of distances at which annihilation actually occurs in protonium. We also analyse the effect of the initial state interaction on two meson branching ratios and underline that it may dramatically change the predictions of those microscopic models which are based only on phase space and simple quark diagrams.     

Quantum J1-J2 antiferromagnet on a stacked square lattice: influence of the interlayer coupling on the ground-state magnetic ordering

Using the coupled-cluster method and the rotation-invariant Green's function method, we study the influence of the interlayer coupling Jperpendicular on the magnetic ordering in the ground state of the spin-1/2 J1-J2 frustrated Heisenberg antiferromagnet (J1-J2 model) on the stacked square lattice. In agreement with known results for the J1-J2 model on the strictly two-dimensional square lattice (Jperpendicular=0), we find that the phases with magnetic long-range order at small J2Jc2 are separated by a magnetically disordered (quantum paramagnetic) ground-state phase. Increasing the interlayer coupling Jperpendicular >0, the parameter region of this phase decreases, and, finally, the quantum paramagnetic phase disappears for quite small Jperpendicular approximately (0.2-0.3)J1.     

The existence of the molecule CLi3 and its ionization potential

The CLi₃ molecule has been observed by desorption when Li(g) permeates through a graphite membrane. The ionization potential of CLi₃ was determined as 4.6 ± 0.3 eV. The ratio of the ion intensities of Li(g) to CLi₃(g) is about 1000 at the experimental temperature.