Piezoelectricity: Quantized Charge Transport Driven by Adiabatic   Deformations
  We study the (zero temperature) quantum piezoelectric response of Harper-like models with broken inversion symmetry. The charge transport in these models is related to topological invariants (Chern numbers). We show that there are arbitrarily small periodic modulations of the atomic positions that lead to nonzero charge transport for the electrons. 
J.E. Avron, J. Berger (Technion) and Y. Last (Caltech)