Underlying mechanism behind high critical temperature in cuprate superconductors

Motivated by recent discovery of anomalously strong near-neighbor attraction in the doped cuprate chains, we revisited the two-dimensional extended Hubbard model at a mean-field level, with the aim of the mechanism behind high critical temperature in cuprate superconductors. Considering the strong spin fluctuations caused by local repulsion, we assume that above $T_c$, the system tends to be in the antiferromagnetic phase, and consequently, the nonlocal superconducting order parameters also undergo the identical spatial modulation below $T_c$. Numerical results show that $T_c$ increases almost linearly with $\left|V\right|$ for sufficiently large $\left|V\right|$, while it increases slowly with $U$ and saturates for sufficiently large $U$. Further theoretical analysis suggests that the underlying mechanism is due to the ultra-narrow property of the effective bands, bestowed by the large antiferromagnetic gap. These findings are of great importance for understanding the commonality among unconventional superconductors and for designing higher-temperature superconducting materials.Comment: Need a major modificatio