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电子空穴气中瞬态导电和绝缘相的超快太赫兹探测

Ultrafast terahertz probes of transient conducting and insulating phases in an electron-hole gas.

作者信息

Kaindl R A, Carnahan M A, Hägele D, Lövenich R, Chemla D S

机构信息

Department of Physics, University of California at Berkeley, and Materials Sciences Division, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

出版信息

Nature. 2003 Jun 12;423(6941):734-8. doi: 10.1038/nature01676.

Abstract

Many-body systems in nature exhibit complexity and self-organization arising from seemingly simple laws. For example, the long-range Coulomb interaction between electrical charges has a simple form, yet is responsible for a plethora of bound states in matter, ranging from the hydrogen atom to complex biochemical structures. Semiconductors form an ideal laboratory for studying many-body interactions of electronic quasiparticles among themselves and with lattice vibrations and light. Oppositely charged electron and hole quasiparticles can coexist in an ionized but correlated plasma, or form bound hydrogen-like pairs called excitons. The pathways between such states, however, remain elusive in near-visible optical experiments that detect a subset of excitons with vanishing centre-of-mass momenta. In contrast, transitions between internal exciton levels, which occur in the far-infrared at terahertz (1012 s(-1)) frequencies, are independent of this restriction, suggesting their use as a probe of electron-hole pair dynamics. Here we employ an ultrafast terahertz probe to investigate directly the dynamical interplay of optically-generated excitons and unbound electron-hole pairs in GaAs quantum wells. Our observations reveal an unexpected quasi-instantaneous excitonic enhancement, the formation of insulating excitons on a 100-ps timescale, and the conditions under which excitonic populations prevail.

摘要

自然界中的多体系统展现出源于看似简单定律的复杂性和自组织性。例如,电荷之间的长程库仑相互作用形式简单,却导致了物质中大量的束缚态,从氢原子到复杂的生化结构。半导体构成了一个理想的实验室,用于研究电子准粒子之间以及与晶格振动和光的多体相互作用。带相反电荷的电子和空穴准粒子可以共存于电离但相关的等离子体中,或者形成称为激子的类似氢的束缚对。然而,在检测质心动量消失的激子子集的近可见光学实验中,这些状态之间的路径仍然难以捉摸。相比之下,在太赫兹(10¹² s⁻¹)频率的远红外区域发生的内激子能级之间的跃迁不受此限制,这表明它们可作为电子 - 空穴对动力学的探针。在这里,我们使用超快太赫兹探针直接研究砷化镓量子阱中光生激子与未束缚电子 - 空穴对的动态相互作用。我们的观察结果揭示了一种意想不到的准瞬时激子增强、在100皮秒时间尺度上绝缘激子的形成以及激子占据主导的条件。

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