二维晶格中的叠套

NESTING IN THE TWO-DIMENSIONAL LATTICE

二维半满晶格的稳定性要考虑次近邻跃迁，此时二聚化δ存在一个临界值δ＿０，同时叠套（Ｎｅｓｔｉｎｇ）分为两种情况：１）当δ≥δ＿０，部分Ｎｅｓｔｉｎｇ，费密面的一部分仍是平直的。２）当δ＜δ＿０，近似Ｎｅｓｔｉｎｇ，费密面是弯的。

It is needed to include the next-nearest hopping for the instability of two-dimensional half-filled lattice.Then there exists a critical value δ_0 of the dimeriza-tion δ. When δ≥δ_0, it is part-nesting, a part of Fermi surface is flat; whereasδ<δ_0, it is only approximate nesting, Fermi surface is curved.