Superconductivity and SDW condensation energies in the 2D Hubbard model and the meaning to the stripe phase

Abstract

The variational Monte Carlo calculations give a finite bulk-limit value of superconducting (SC) condensation energy E_{cond} in the 2D Hubbard model with next-nearest-site transfer energy t' when electron density \rho\ge 0.84 with -0.25\le t' \le -0.10; our energy unit is the transfer energy between the nearest-neighbor (n.n.) sites. However, the SDW E_{cond} computed by the same method is larger than the SC one in such a region. This suggests that the SC region is very restricted, if it exists. When we improved the trial wave function taking into account the n.n.-site correlation, the SC E_{cond} increased moderately while the SDW E_{cond} decreased considerably. With this modified variational Monte Carlo method we have found a set of parameter values for which the bulk-limit SC E_{cond} is finite whereas that for the SDW vanishes. The SC E_{cond} obtained in both ways around the optimal doping is in fair agreement with the experimental value \sim 0.26 meV/site for YBCO estimated from the specific heat and the critical magnetic field, in contrast to the case of the t-J model which gives a value larger by almost two orders of magnitude.


Article outline

1.Introduction
2.Our preceding results
3.Competition with the SDW
4.Improvement of the trial wave functions taking into account the n.n. correlation
5.Reasoning on the SC phase in the underdoped region