Polarons and bipolarons in a two-dimensional square lattice

Superconducting Polarons and Bipolarons

The seminal work by Bardeen, Cooper and Schrieffer (BCS) extended further by Eliashberg to the intermediate coupling regime solved one of the major scientific problems of Condensed Matter Physics in the last century. The BCS theory provides qualitative and in many cases quantitative descriptions of low-temperature superconducting metals and their alloys, and some novel high-temperature supercon...

A Novel Structure for Optical Channel Drop Filter using Two-Dimensional Photonic Crystals with Square Lattice

In the present paper a novel structure for optical channel drop filter (CDF) based on photonic crystal ring resonator with circular core has been proposed. In order to design the proposed CDF, the plan wave expansion (PWE) method is applied for calculation of band structure and photonic band gap while the transmission characteristics of proposed CDF have been calculated using the finite differe...

Lattice and spin polarons in two dimensions

Polarons and bipolarons in strongly interacting electron-phonon systems.

The Holstein Hubbard and Holstein t–J models are studied for a wide range of phonon frequencies, electron–electron and electron–phonon interaction strengths on finite lattices with up to ten sites by means of direct Lanczos diagonalization. Previously the necessary truncation of the phononic Hilbert space caused serious limitations to either very small systems (four or even two sites) or to wea...

Folding transitions of the square – diagonal two – dimensional lattice ∗

The phase diagram of a vertex model introduced by P. Di Francesco (Nucl. Phys. B 525, 507 1998) representing the configurations of a square lattice which can fold with different bending energies along the main axes and the diagonals has been studied by Cluster Variation Method. A very rich structure with partially and completely folded phases, different disordered phases and a flat phase is fou...