Induced local spin-singlet amplitude and pseudogap in high-T_c cuprates

In this paper we show that local spin-singlet amplitude with d-wave symmetry, 〈|Δ_d(0)|²〉, can be induced by short-range spin correlations even in the absence of pairing interactions. Fluctuation theory is formulated to make a connection between pseudogap temperature T^*, pseudogap size Δ_pg, and 〈|Δ_d(0)|²〉. In the present scenario for the pseudogap, the normal-state pseudogap is caused by the induced local spin-singlet amplitude due to short-range spin correlations, which compete in the low-energy sector with superconducting correlations to make T_c go to zero near half filling. Calculated T^* falls from a high value onto the T_c line and closely follows the mean-field Néel temperature T_N^MF. The calculated Δ_pg is in good agreement with experimental results. We propose an experiment in which the present scenario can be critically tested.