Doping dependence of the (pi, pi) shadow band in La-based cuprates studied by angle-resolved photoemission spectroscopy

The (pi, pi) shadow band (SB) in the La-based cuprate family (La214) was studied by angle-resolved photoemission spectroscopy over a wide doping range from x = 0.01 to x = 0.25. Unlike the well-studied case of the Bi-based cuprate family, an overall strong, monotonic doping dependence of the SB intensity at the Fermi level (E-F) was observed. In contrast to a previous report for the presence of the SB only close to x = 1/8, we found that it exists in a wide doping range, associated with a doping-independent (pi, pi) wave vector but a strongly doping-dependent intensity: it is strongest at x similar to 0.03 and systematically diminishes as the doping increases until it becomes negligible in the overdoped regime. This SB with the observed doping dependence of intensity can in principle be caused by the antiferromagnetic fluctuations or a particular form of low-temperature orthorhombic lattice distortion known to persist up to x similar to 0.21 in the system, with both being weakened with increasing doping. However, a detailed binding-energy-dependent analysis of the SB at x = 0.07 does not appear to support the former interpretation, leaving the latter as a more plausible candidate, despite a challenge in quantitatively linking the doping dependences of the SB intensity and the magnitude of the lattice distortion. Our finding highlights the necessity for a careful and global consideration of the inherent structural complications for correctly understanding the cuprate Fermiology and its microscopic implication.