关联电子系统中的隐藏玻色-爱因斯坦奇异性
Hidden Bose-Einstein Singularities in Correlated Electron Systems
AI总结：
本文理论揭示关联电子系统中由玻色-爱因斯坦统计配对涨落引起的隐藏奇异性，其与相变不同但相关，并导致负-U Hubbard模型超导转变温度以上的赝能隙行为。
摘要：
理论上阐明了关联电子系统中由电子-电子或电子-空穴气泡的配对涨落引起的隐藏奇异性，这些配对涨落服从玻色-爱因斯坦统计。研究表明，每个配对涨落的关联函数在零松原频率分支上存在一个界限，类似于理想玻色气体的化学势。一旦达到该界限，自能开始获得与格林函数本身成比例的分量，即所谓的单粒子可约结构，以将关联函数保持在界限内。这些奇异性与具有对称性破缺的相变密切相关，但又有所不同。穿过这些奇异性必然伴随着激发阈值附近单粒子态密度的变化，例如本文发现的负-U Hubbard模型在超导转变温度以上的赝能隙行为。
英文摘要：
Hidden singularities in correlated electron systems, which are caused by pair fluctuations of electron-electron or electron-hole bubbles obeying Bose-Einstein statistics, are clarified theoretically. The correlation function of each pair fluctuation is shown to have a bound in the zero Matsubara frequency branch, similarly to the chemical potential of ideal Bose gases. Once the bound is reached, the self-energy starts to acquire a component proportional to Green's function itself, i.e., the structure called one-particle reducible, to keep the correlation function within the bound. The singularities are closely related to, but distinct from, phase transitions with broken symmetries. Passing down through them is necessarily accompanied by a change in the single-particle density of states around the excitation threshold, such as the pseudogap behavior found here for the negative-$U$ Hubbard model above the superconducting transition temperature.
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