Indexed on: 09 Aug '16Published on: 08 Aug '16Published in: Nature Physics
High-temperature superconductivity in the cuprates is widely believed to originate from an antiferromagnetic parent Mott insulator when doped with charge carriers1. In terms of the electronic structure, the key question is how the large charge transfer gap evolves into the pseudogap and then the d-wave superconducting gap2, 3, 4, 5. However, whether superconductivity or some other symmetry-breaking state (such as charge or spin orders) emerges first on doping a Mott insulator is debatable. To address these issues, here we use scanning tunnelling microscopy to investigate the local electronic structure of lightly doped cuprates in the antiferromagnetic insulating regime. We show that the doped charge induces a spectral weight transfer from the high-energy Hubbard bands to low-energy states within the charge transfer gap. With increasing doping, a V-shaped density-of-state suppression reminiscent of the pseudogap occurs at the Fermi level, which is accompanied by the emergence of chequerboard charge order. Our data suggest that the cuprates first become a charge-ordered insulator on doping, and the Fermi surface and high-temperature superconductivity becomes manifest on further doping.