@article {4923,
	title = {Polarization and adiabatic pumping in inhomogeneous crystals},
	journal = {Physical Review Letters},
	year = {2009},
	doi = {10.1103/PhysRevLett.102.087602},
	author = {Di Xiao and Junren Shi and Dennis P. Clougherty and Qian Niu}
}
