Spiral Spin Order and Transport Anisotropy in Underdoped Cuprates
  We discuss the spiral spin density wave model and its application to explain properties of underdoped La$_{2-x}$Sr$_x$CuO$_4$. We argue that the spiral picture is theoretically well justified in the context of the extended $t-J$ model, and then show that it can explain a number of observed features, such as the location and symmetry of the incommensurate peaks in elastic neutron scattering, as well as the in-plane resistivity anisotropy. A consistent description of the low doping region (below 10% or so) emerges from the spiral formulation, in which the holes show no tendency towards any type of charge order and the physics is purely spin driven. 
Valeri N. Kotov and Oleg P. Sushkov