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Composite fermion theory for pseudogap phenomena and superconductivity in underdoped cuprate superconductors

机译：复合费米子理论研究伪掺杂现象和超导铜酸盐超导体

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摘要

We study pseudogap phenomena and Fermi-arc formation experimentally observed in typical two-dimensional doped Mott insulators, namely, underdoped cuprate superconductors. To develop a physically unequivocal theory, we start from the slave-boson mean-field theory for the Hubbard model on a square lattice. Our crucial step is to further take into account the charge dynamics and fluctuations. The extra charge fluctuations seriously modify low-energy single-particle spectra of doped Mott insulators near the Fermi level: An electron added around an empty site (or a hole added around a doubly occupied site) constitutes composite fermion (cofermion), called holo-electron (or doublo-hole) at low energy in distinction from the normal quasiparticles. These unexplored composite fermions substantiate the extra charge fluctuation. We show that the quasiparticles hybridize with the holo-electrons and doublo-holes. The resultant hybridization gap is identified as the pseudogap observed in the underdoped region of the high-T_c cuprates. Because the Fermi level crosses the top (bottom) of the low-energy band formed just below (above) the hybridization gap in the hole-doped (electron-doped) case, it causes a Fermi-surface reconstruction, namely, a topological change in the Fermi surface forced by the penetration of zeros of the quasiparticle Green's function. This reconstruction signals the emergence of a non-Fermi-liquid phase. The pseudogap and the resultant formation of pocket or arc of the Fermi surface reproduce the experimental results for the cuprate superconductors in the underdoped region. The pairing channel opens not only between two quasiparticles, but also between a quasiparticle and a cofermion. This pairing solves the puzzle of the dichotomy between the d-wave superconductivity and the precursors of the the insulating gap in the antinodal region. We propose and analyze them as the mechanism of the high-temperature superconductivity for the cuprates.
机译：我们研究了在典型的二维掺杂Mott绝缘子（即，掺杂不足的铜酸盐超导体）中实验观察到的伪间隙现象和费米电弧形成。为了发展物理上明确的理论，我们从正方形框架上的Hubbard模型的从玻色子平均场理论开始。我们的关键步骤是进一步考虑充电动态和波动。额外的电荷波动会严重改变费米能级附近的掺杂Mott绝缘子的低能单粒子光谱：在空位周围添加的电子（或在双倍占据位点周围添加的空穴）构成复合费米子（共价铁），称为全息-与正常准粒子不同的低能量电子（或杜布罗空穴）。这些未探索的复合费米子证实了额外的电荷波动。我们显示准粒子与全电子和双孔杂化。所得的杂交间隙被鉴定为在高T_c铜酸盐的低掺杂区中观察到的伪间隙。由于费米能级越过在空穴掺杂（电子掺杂）情况下杂化间隙正下方（上方）形成的低能带的顶部（底部），因此会引起费米表面重构，即拓扑变化在费米表面上，由于准粒子格林函数的零的渗透而被迫。这种重建表明非费米液相的出现。伪间隙以及由此形成的费米表面的凹坑或弧形再现了低掺杂区铜酸盐超导体的实验结果。配对通道不仅在两个准粒子之间打开，而且在准粒子和钴铁蛋白之间打开。这种配对解决了d波超导性与反节点区域中绝缘间隙前体之间二分法的难题。我们提出并对其进行分析，将其作为铜酸盐的高温超导机理。

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