Ogawa Tetsuo, Tomio Yuh, Asano Kenichi
Department of Physics, Osaka University and CREST, JST, Toyonaka, Osaka 560-0043, Japan.
J Phys Condens Matter. 2007 Jul 25;19(29):295205. doi: 10.1088/0953-8984/19/29/295205. Epub 2007 Jun 11.
Quantum condensation of electron-hole (e-h) systems in photoexcited semiconductors is reviewed from a theoretical viewpoint, stressing the exciton Bose-Einstein condensation (BEC), the e-h BCS-type condensed state, the exciton Mott transition, and the biexciton crystallization. First, we discuss the crossover between the exciton BEC and the e-h BCS states at low temperature using the self-consistent t-matrix and local approximations, applied to the high-dimensional two-band Hubbard model with both repulsive and attractive on-site interactions. We also study the metal-insulator transition (called the 'exciton Mott transition') at zero and finite temperatures, investigated with the dynamical mean-field theory. Away from half-filling we find excitonic/biexcitonic insulating phases and the first-order transition between metallic and insulating states. Second, in a one-dimensional e-h system, we employ the exciton bosonization and renormalization-group techniques to clarify quantum orders at zero temperature. The most probable ground state exhibits the biexciton crystallization, which reflects the Tomonaga-Luttinger liquid properties, the e-h backward scattering, and the long-range Coulomb interaction. The one-dimensional e-h system is insulating even at the high-density limit, hence the exciton Mott transition never occurs at zero temperature in one dimension.
从理论角度对光激发半导体中电子 - 空穴（e - h）系统的量子凝聚进行了综述，重点讨论了激子玻色 - 爱因斯坦凝聚（BEC）、e - h BCS型凝聚态、激子莫特转变和双激子结晶。首先，我们使用自洽t矩阵和局域近似，应用于具有排斥和吸引在位相互作用的高维两带哈伯德模型，讨论低温下激子BEC和e - h BCS态之间的交叉。我们还研究了零温和有限温度下的金属 - 绝缘体转变（称为“激子莫特转变”），采用动态平均场理论进行研究。在远离半填充时，我们发现了激子/双激子绝缘相以及金属态和绝缘态之间的一级转变。其次，在一维e - h系统中，我们采用激子玻色化和重整化群技术来阐明零温下的量子序。最可能的基态表现出双激子结晶，这反映了汤川 - 卢廷格液体性质、e - h背散射和长程库仑相互作用。一维e - h系统即使在高密度极限下也是绝缘的，因此在一维中零温下激子莫特转变不会发生。
