Possible isotope effect on the resonance peak formation in high-Tc_c cuprates

Starting from the three-band $p-d$ Hubbard Hamiltonian we derive an effective $t-J$ model including electron-phonon interaction of quasiparticles with optical phonons. Within the effective Hamiltonian we analyze the influence of electronic correlations and electron-phonon interaction on the dynamical spin susceptibility in layered cuprates. We find a huge isotope effect on the resonance peak in the magnetic spin susceptibility, ${Im}\chi({\bf q},\omega)$, seen by inelastic neutron scattering. It results from both the electron-phonon coupling and the electronic correlation effects taken into account beyond random phase approximation(RPA) scheme. We find at optimal doping the isotope coeffiecient $\alpha_{res} \approx 0.35$ which can be further tested experimentally.Comment: revised version, new figure is added. Phys. Rev. B 69, 0945XX (2004); in pres

Fractal characteristics of seismic process in rock mass surrounding the excavation at mining. Mathematical modelling and analysis

It is shown in the paper that the system of equations of solid mechanics, which has a mixed type, demonstrate the most common features of evolution of nonlinear dynamic systems. Previous investigations of seismic process were carried out on the base of simplified (sand-pile, land-slide) models which gave a graph of recurrence of seismic events and information about the state of self-organized criticality (SOC). However, these simplified models do not contain the information about the stress-strain state of the loaded geomedia and its proximity to the critical state. In the proposed paper the model of rock mass with excavation is constructed and general step of roof caving is modelled. On the base of these modelling the formation of critical state in loaded geomedia is studied. The fluctuations of stress-strain state at different points of geomedia are studied as the reflection of fracture process occurring in the main elements of rock mass: roof and floor, when the coal face is advanced. It is shown that the PDF dependencies, amplitude-frequency characteristics reflect the state of the rock mass and might be considered as the fractal characteristics of fracture process within. The evolution of these dependencies shows the dramatic change when the critical state is formed in the rock mass surrounding the underground opening

Dynamical charge and spin susceptibilities in a frame of t-J-G model

We have calculated the dynamical charge and spin susceptibilities using the new analytical expression obtained beyond a conventional random phase approximation scheme. Both susceptibilities are strongly peaked along a contour around wave vector Q = (π, π). We have analyzed the dispersions of the collective excitations near Q = (π, π) corresponding to a spin density wave and charge density wave modes, respectively. In addition we have calculated the momentum dependence of the imaginary part of the charge and spin susceptibilities along the instability contour and show that both susceptibilities display a maximum around the points (π, ±q 0), (±q0,π) in Brillouine zone with decreasing temperature that indicates that the stripe-like instability may become preferable. © 2002 Plenum Publishing Corporation

Possible isotope effect on the resonance peak formation in high-T c cuprates

Within effective t-J Hamiltonian we analyze the influence of electronic correlations and electron-phonon interaction on the dynamical spin susceptibility in layered cuprates. We find an isotope effect on the resonance peak in the magnetic spin susceptibility Im χ(q,ω), seen by inelastic neutron scattering. It results from both the electron-phonon coupling and the electronic correlation effects taken into account beyond random-phase approximation scheme. We find at optimal doping the isotope coefficient αres≈0.4 which can be further tested experimentally