Hopping magneto-transport via nonzero orbital momentum states and organic magnetoresistance

TL;DR

This paper extends the theory of hopping magnetoresistance to include states with nonzero orbital momentum, explaining large low-field magnetoresistance in organic materials through wave function expansion and degeneracy lifting effects.

Contribution

It introduces a new theoretical framework for hopping magnetoresistance involving nonzero orbital momentum states, explaining phenomena in organic magnetoresistance.

Findings

Weak magnetic fields can expand wave functions with positive orbital quantum numbers.

Negative magnetoresistance can occur when orbital degeneracy is lifted.

The theory explains large low-field magnetoresistance in organic materials.

Abstract

In hopping magnetoresistance of doped insulators, an applied magnetic field shrinks the electron (hole) s-wave function of a donor or an acceptor and this reduces the overlap between hopping sites resulting in the positive magnetoresistance quadratic in a weak magnetic field, B. We extend the theory of hopping magnetoresistance to states with nonzero orbital momenta. Different from s-states, a weak magnetic field expands the electron (hole) wave functions with positive magnetic quantum numbers, m > 0, and shrinks the states with negative m in a wide region outside the point defect. This together with a magnetic-field dependence of injection/ionization rates results in a negative weak-field magnetoresistance, which is linear in B when the orbital degeneracy is lifted. The theory provides a possible explanation of a large low-field magnetoresistance in disordered pi-conjugated organic materials (OMAR).