  The pairing mechanism of high temperature superconductivity in cuprates is
regarded as one of the most challenging issues that we are facing now. The core
issue is about how the Cooper pairs are formed. There are plenty pictures
concerning the pairing manner, and some of them postulate local pairing of
charge freedom through the strong correlation effect. Here we report the spin
resolved tunnelling measurements on extremely underdoped Bi2Sr2-xLaxCuO6-delta.
Our data reveal that, when holes are doped into the system, the
antiferromagnetic order is destroyed together with the filling up of the charge
transfer gap by some density of states (DOS) with a maximum at about 200 meV.
Consequently, an electronic structure with 4a0x4a0 basic plaquettes gradually
emerges, and they become more populated versus further hole doping. In the
central part of each plaquette, there are three unidirectional bars (along the
Cu-O bond) enlightened by the enhanced peaks of coherence-like DOS at about
+-25 meV, and the intensity is especially pronounced at oxygen sites. For the
first time, we reveal an internal nematic pattern of these pairing related
states which exhibit a feature of precursor gap for superconductivity. We argue
that this confined nematic state within one 4a0x4a0 plaquette constitutes
naturally the local pairing format. Our work shed new light in unraveling the
longstanding puzzle of pairing mechanism in cuprate superconductors.
