Regensburg 1998 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 20: Korrelierte Elektronen (Theorie) I
TT 20.3: Vortrag
Donnerstag, 26. März 1998, 15:15–15:30, H 18
Gradient expansions for the t-J and Hubbard models — •A. Muramatsu1 and M. Imada2 — 1Institut für Theoretische Physik III, Universit"at Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart. — 2Institute for Solid State Physics, University of Tokyo, 7-22-1 Roppongi, Minato-Ku, Tokyo.
The t-J and Hubbard models are treated by means of a gradient expansion, in order to extract the critical properties close to the transition to the antiferromagnetic state as a function of doping. An exact representation of fermionic operators is used such that dopant holes are described by spinless fermions and the constraint supressing doubly occupancy becomes an holonomic one. The results so far indicate that nearest-neighbor (nn) hopping becomes irrelevant whereas next to nn hopping is relevant in two dimensions. In particular, in the case of the Hubbard model in strong coupling (t-J with three-sites term), this leads to flat bands around the points (± π,0) and (0,± π), and a band-width ∼ J. Finally, we discuss the role of pair-hopping from the three-sites term in connection with the pseudo-gap observed in recent photoemission experiments in high Tc superconductors above Tc.