Three observations on the ARPES data of the cuprate superconductors - what the AF spin fluctuation can do and what it cannot
We discuss the origin of the pseudogap phenomena in the cuprate superconductors by analyzing three recent ARPES observations from the perspective of the spin-Fermion model. Firstly, we show that the recent observation of the vanishing of the pseudogap around (π,0) in the electron-doped cuprate Pr1.3−xLa0.7CexCuO4 is consistent with the AF band folding picture of the pseudogap in the electron-doped cuprates, provided that we assume a strongly momentum dependent quasi-particle scattering rate on the Fermi surface [1,2]. Secondly, we argue that the pseudogap in the hole-doped cuprates is unlikely an AF band folding gap, since the spin fluctuation in the hole-doped cuprates is much more short-ranged and dynamical in nature than that in the electron-doped cuprates. In particular, we show that electron pairing is indispensable to eliminate the Fermi level crossing along (π,0)-(π,π) in a way that is consistent with the ARPES observation in the under-doped Bi-2201 system around T* [3,4]. Nevertheless, we find that the AF spin fluctuation in the hole-doped cuprates is responsible for the emergence of the broad high energy hump structure in the anti-nodal region, and the mismatch between the back-bending momentum of the hump maximum and the underlying Fermi momentum along (π,0)-(π,π), and in particular, the extremely flatness of the anti-nodal quasi-particle dispersion in the superconducting state [5,6]. We argue that the particle-hole symmetry breaking should better be studied in the energy space, rather than in the momentum space . Lastly, we show that the recent observation of the critical behavior at the pseudogap end point is consistent with the spin-Fermion picture [7,8], even though the local spin in the cuprates is far from critical at such a high doping level, if one note the singular AF response of the quasi-particle system at the VHS doping.
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