Protected nodal electron pocket from multiple-Q ordering in underdoped   high temperature superconductors
  A multiple wavevector (Q) reconstruction of the Fermi surface is shown to yield a profoundly different electronic structure to that characteristic of single wavevector reconstruction, despite their proximity in energy. We consider the specific case in which ordering is generated by Qx = [2{\pi}a, 0] and Qy = [0,2{\pi}b] (in which a = b = 1/4) - similar to those identified in neutron diffraction and scanning tunneling microscopy experiments, and more generally show that an isolated pocket adjacent to the nodal point knodal = [\pm {\pi}/2, \pm {\pi}/2] is a protected feature of such a multiple-Q model, potentially corresponding to the nodal 'Fermi arcs' observed in photoemission and the small size of the electronic heat capacity found in high magnetic fields - importantly, containing electron carriers which can yield negative Hall and Seebeck coefficients observed in high magnetic fields. 
N. Harrison, S. E. Sebastian
cond-mat.str-el