科研之友
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摘要
Recently. Comes etal. [1] have visualized the gap formation in nanoscale regions (NRs) above the critical temperature T-c in the high-T-c superconductor Bi2Sr2CaCu2O8+delta It has been found that, as the temperature lowers, the NRs expand in the bulk superconducting state consisted of inhomogeneities. The fact that the size of the inhomogeneity [2] is close to the minimal size of the NR [1] leads to a conclusion that the superconducting phase is a result of these overlapped NRs. In the present paper we perform the charge and percolation regime analysis of NRs and show that at the first critical doping x(c1), when the superconductivity starts on, each NR carries the positive electric charge one in units of electron charge, thus we attribute the NR to a single hole boson, and the percolation lines connecting these bosons emerge. At the second critical doping x(c2), when the superconductivity disappears, our analysis demonstrates that the charge of each NR equals two. The origin of x(c2) can be understood by introducing additional normal phase hole fermions in NRs, whose concentration appearing above x(c1) increases smoothly with the doping and breaks the percolation lines of bosons at x(c2). The last one results in disappearing the bulk bosonic property of the pseudogap (PG) region, which explains the upper bound for existence of vortices in Nernst effect [3]. Since Comes et al. [1] has demonstrated the absence of NRs at the PG boundary one can conclude that along this boundary, as well as in x(c2), all bosons disappear. As justification of appearance of single bosons, the bosonization of 2D fermions is rigorously proven using the concept of anyons. The linear density dependence of the energy gap between excited fermionic and bosonic ground states describes the Uemura relation for 20 superconductors.
- 出版日期2011-8
