Collapse of the Fermi surface and fingerprints of order in the pseudogap   state of cuprate superconductors
  The Fermi surface in the state of cuprates is highly unusual because it appears to consist of disconnected segments called arcs. Their very existence challenges the traditional concept of a Fermi surface as closed contours of gapless excitations in momentum space. The length of the arcs in the pseudogap state was thought to linearly increase with temperature, pointing to the existence of a nodal liquid state below T*. These results were interpreted as an interplay of a d-wave pairing gap and strong scattering. Understanding the properties of the arcs is a pre-requisite to understanding the origin of the pseudogap and the physics of the cuprates. Here we use a novel approach to detect the energy gaps based on the temperature dependence of the density of states. With a significantly improved sensitivity, we demonstrate that the arcs form rapidly at T* and their length remains surprisingly constant over an extended temperature range between T* and Tarc, consistent with the presence of an ordered state below T*. These arcs span fixed points in the momentum space defining a set of wave vectors, which are the fingerprints of the ordered state that causes the pseudogap. 
Takeshi Kondo, Ari Palczewski, Yoichiro Hamaya, K. Ogawa, Tsunehiro   Takeuchi, J. S. Wen, G. Z. J. Xu, Genda Gu and Adam Ka...
cond-mat.supr-con cond-mat.str-el