27.9.2011, 17:00 Jungiusstr. 9, Seminarraum 3 | SFB 668 - Kolloquium **Prof. V. Kagalovsky (SCE, Israel):**
## Spin-flip scattering at quantum Hall transitionWe find exact analytical expression for spin-dependent transmission coefficients of a charged particle through a saddle point potential in a perpendicular magnetic field in the presence of a nuclear spin. We formulate a generalized Chalker--Coddington network model describing quantum Hall effect in such bispinor (electron + nucleus) system.
Spin-flip scattering creates a metallic state in a finite range around the critical energy of quantum Hall transition. As a result we find
that the usual insulating phases with Hall conductance are separated
by novel metallic phases. We discuss the construction of an effective scattering matrix for the electron only, achieved by statistical averaging over nuclear spins. We also consider an electron coupled by spin-spin interaction to arbitrary number of nuclei. We find energies and degeneracies of the eigenstates. We discuss possible Hall conductivity graphs at the critical transition. |