Charge density waves with unconventional order parameters, for instance, with d-wave symmetry (DDW), may be relevant in the underdoped regime of high-T_c cuprates or other quasi-one or two dimensional metals. A DDW state is characterized by two branches of low-lying electronic excitations. The resulting quantum mechanical current has an inter-branch component which leads to an additional mass term in the expression for the Hall conductivity. This extra mass term is parametrically enhanced near the ``hot spots'' of fermionic dispersion and is non-neglegible as is shown by numerical calculations of the Hall number in the DDW state.
@article{arxiv.cond-mat/0405194,
title = {The Hall conductivity in unconventional charge density wave systems},
author = {D. N. Aristov and R. Zeyher},
journal= {arXiv preprint arXiv:cond-mat/0405194},
year = {2007}
}