Puzzling magnetoresistance

A wide range of new functional electronic materials are layered metals whose electrical resistance changes significantly in the presence of a magnetic field. One example is the giant magnetoresistance (GMR) materials, recognized in the 2007 Nobel Prize in Physics. Many of the latest memories in computers and iPods are based on GMR materials.

In semi-classical transport theory for conventional metals magnetoresistance arises from the Lorentz force (F=vxB) on the electrons. This force is zero when the magnetic field and current are parallel and maximal when the field and current are perpendicular. However, in a structurally and chemically diverse range of layered metals there is a large magnetoresistance when the magnetic field and current are parallel, both being perpendicular to the layers. In contrast, the interlayer magnetoresistance is small when the field is parallel to the layers. This unusual angular dependence of the magnetoresistance has been observed in several organic charge transfer salts, intercalated graphite, ruthenates, and semiconductor superlattices.
These slides show examples of the strange angle-dependent magnetoresistance for these materials.

What is the origin of this non-classical magnetoresistance?

I have been working on this for several years. It is a hard problem, which appears to be related to the problem of magic angles in magnetoresistance in organic metals. This paper discusses in more detail some of the issues.

I welcome new ideas.