only the case of weak electric fields will be considered, so that additional touching points do not arise. What happens when both the electric and magnetic fields are strong, or when the electric field is strong but the magnetic field weak, is a topic for further investigation.

There are also at least two relevant works in the carbon nanotube literature. In Ref. the low energy spectrum of a carbon nanotube in a magnetic field that is transverse to the axial direction is calculated analytically. In Ref. the same system is considered and shown to support a quantized Hall current in the axial direction. The nanotube system can be considered a special one-dimensional case of the general two dimensional system considered below. In order to induce a gap in the nanotube spectrum, an electric field must be applied parallel to the magnetic field. This was not considered in the cited references. Consequently, the Hall effect found in Ref. is fundamentally different from the Hall effect considered here. This will be discussed in more detail below. However some results that hold for the system discussed in this work should also hold for the nanotube system. Where there should be agreement between results 