Delocalization of Wannier-Stark ladders by phonons: Tunneling and stretched polarons

¹ Department of Physics and Astronomy, and Condensed Matter and Surface Sciences Program, Ohio University - Athens, OH 45701-2979, USA
² Institute of Semiconductor Physics, RAS, Siberian Branch 630090 Novosibirsk, Russia

Received: 22 November 2001
Accepted: 22 March 2002

Abstract

We study the coherent dynamics of a Holstein polaron in strong electric fields. A detailed analytical and numerical analysis shows that even for small hopping constant and weak electron-phonon interaction, polaron states can become delocalized if a resonance condition develops between the original Wannier-Stark states and the phonon modes, yielding both tunneling and “stretched” polarons. The unusual stretched polarons are characterized by a phonon cloud that trails the electron, instead of accompanying it. In general, our novel approach allows us to show that the polaron spectrum has a complex nearly fractal structure, due to the coherent coupling between states in the Cayley tree which describes the relevant Hilbert space. The eigenstates of a finite ladder are analyzed in terms of the observable tunneling and optical properties of the system.