A. S. Mishchenko

Lattice Dynamics of Intermediate Valence Semiconductor SmB6.

All acoustic and the lowest optic branches in three main symmetry directions have been determined by inelastic neutron scattering at room temperature using a double isotope monocrystal 154Sm11B6. In comparison with the integer valence system LaB6 the phonons are softer, and the LA branches exhibit remarkable anomalies. These features are interpreted on the basis of a specific coupling of the lattice vibrations with the dipole (f-d) and monopole (f-f) excitations of the Sm shells, the latter being characteristic for the mixed valence semiconductor. A weak broad signal has been observed in the energy gap between acoustic and optic modes, which can be ascribed to an additional mode appearing due to the nonadiabatic interaction of phonons with valence fluctuations.

Charge dynamics of doped holes in high Tc cuprate superconductors: A clue from optical conductivity

The charge dynamics in weakly hole doped high temperature superconductors is studied in terms of the accurate numerical solution to a model of a single hole interacting with a quantum lattice in an antiferromagnetic background, and accurate far-infrared ellipsometry measurements. The experimentally observed two electronic bands in the infrared spectrum can be identified in terms of the interplay between the electron correlation and electron-phonon interaction resolving the long standing mystery of the midinfrared band.

Sharp Transition for Single Polarons in the One-Dimensional Su-Schrieffer-Heeger Model

We study a single polaron in the Su-Schrieffer-Heeger (SSH) model using four different techniques (three numerical and one analytical). Polarons show a smooth crossover from weak to strong coupling, as a function of the electron-phonon coupling strength λ, in all models where this coupling depends only on phonon momentum q. In the SSH model the coupling also depends on the electron momentum k; we find it has a sharp transition, at a critical coupling strength λ(c), between states with zero and nonzero momentum of the ground state. All other properties of the polaron are also singular at λ=λ(c). This result is representative of all polarons with coupling depending on k and q, and will have important experimental consequences (e.g., in angle-resolved photoemission spectroscopy and conductivity experiments).

INTERPLAY BETWEEN HEAVY FERMIONS AND CRYSTAL-FIELD EXCITATION IN KONDO LATTICES : LOW-TEMPERATURE THERMODYNAMICS AND INELASTIC NEUTRON SCATTERING SPEC TRA OF CENISN

The microscopic theory of interaction between the heavy fermions and the crystal field excitations in Kondo lattices is presented. It is shown that the heavy-fermion spectrum scaled by the Kondo temperature

Quantum dynamics of the Hubbard-Holstein model in equilibrium and nonequilibrium: application to pump-probe phenomena.

T_K

Single-hole spectral function and spin-charge separation in the t-J model

can be modified by the crystal field excitations with the energy

Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system

\Delta_{CF}

Diagrammatic Quantum Monte Carlo for Two-Body Problem: Exciton

provided the inequality

Critical phenomena of emergent magnetic monopoles in a chiral magnet.

\Delta_{CF}<T_K

Self-trapping of polarons in the Rashba-Pekar model

is realized. On the base of general description of excitation spectrum the detailed qualitative and quantitative explanation of anisotropic inelastic neutron scattering spectra and low-temperature specific heat of orthorhombic CeNiSn is given. The theory resolves the apparent contradiction between the metallic conductivity and the gap-wise behavior of thermodynamic properties and spin response of CeNiSn at low temperatures.