In a usual electric conductor, running an electric current perpendicular to a magnetic field produces a transverse electric field -- this is the Hall effect. In a recent study, however, Phuan Ong's group at Princeton explored a material (KHgSb) for which the Hall effect goes away completely when the magnetic field is sufficiently strong. On the other hand, the longitudinal conductivity remains finite.
Ong's group and I were able to explain this strange finding based on two ideas:
- The crystal structure of the material has a "non-symmorphic" symmetry that gives rise to "double quantum spin Hall" states which carry transverse current in equal and opposite directions on the material's surface.
- The magnetic field causes the bulk electrons to localize onto impurity states, a phenomenon sometimes called "magnetic freezeout".