Self-trapped electron states in nanotubes

TL;DR

This paper investigates self-trapped electron states (polarons) in deformable nanotubes, revealing how electron-phonon interactions lead to different localized states depending on coupling strength and nanotube diameter.

Contribution

It introduces a Hamiltonian model for polarons in nanotubes and numerically explores the transition between ring-like and localized solutions based on coupling and diameter.

Findings

Ring-like polaron solutions at weak coupling

Localized polaron states at strong coupling

Transition depends on nanotube diameter

Abstract

We study numerically self-trapped (polaron) states of quasiparticles (electrons, holes or excitons) in a deformable nanotube formed by a hexagonal lattice, wrapped into a cylinder (carbon- and boron nitride-type nanotube structures). We present a Hamiltonian for such a system taking into account an electron-phonon interaction, and determine conditions under which the lowest energy states are polarons.We compute a large class of numerical solutions of this model for a wide range of the parameters. We show that at not too strong electron-phonon coupling, the system admits ring-like localized solutions wrapped around the nanotube (the charge carrier is localized along the nanotube axis and uniformly distributed with respect to the azimuthal coordinate). At stronger coupling, solutions are localized on very few lattice sites in both directions of the nanotube. The transition from one type solution to the other one depends on the diameter of the nanotube. We show that for the values of the carbon nanotube parameters, the polarons have a ring-like structure wrapped around the nanotube with a profile resembling that of the nonlinear Schrodinger soliton.