Electronic structure of lightly doped insulating cuprates revealed by STM
Peng Cai1, Wei Ruan1, Cun Ye1, Xiaodong Zhou1, Yingying Peng2, Xingjiang Zhou2, and Yayu Wang1
1
State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua
University, Beijing 100084, P. R. China
2
National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter
Physics, Institute of Physics, Chinese Academy of Science, Beijing 100190, China
A long standing mystery in the cuprates is how the pseudogap and
superconducting gap emerge when charge carriers are doped into the charge-transfer
type parent Mott insulator. We have performed scanning tunneling microscopy studies
on severely underdoped Bi2Sr2-xLaxCuO6 in the antiferromagnetic insulating state.
The large energy window covered by the tunneling spectroscopy allows us to
simultaneously capture the features of the full charge transfer gap and the pseudogap
at atomic scale. We show that the pseudogap spectral features evolve smoothly from
the charge transfer gap in parent Mott insulator through a spatially localized broad
in-gap state. The gap size, spectral weight and tunneling asymmetry of the pseudogap
are shown to have clear correlation with the spectral weight of the upper Hubbard
band. The direct visualization of the spectral weight transfer process in the Mottness
regime sheds new light on the electronic structure evolution of the cuprates.