Electron-hole bilayers: Excitonic phases and collective modes

电子空穴双层：激子相和集体模式

• 批准号: EP/H017720/1
• 负责人: David Ritchie
• 金额: $ 125.57万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FH017720%2F1
• 关键词: Electron; hole; bilayers; Excitonic; phases

When two dissimilar semiconductors are in contact their conduction and valence bands are generally not continuous across the interface. The profile of the bands may resemble a potential well that can trap electrons and holes. These trapped carriers are highly mobile parallel to the interface but are confined to a few tens of nanometers in the third dimension. This band engineering principle gave birth to Silicon MOSFETs and Gallium Arsenide based High electron mobility transistors (HEMT) that revolutionised electronics. At the same time these devices opened up the fascinating world of 2-dimensional electronic systems. Very recent technological advances have enabled the fabrication of devices in which a sheet of 2-dimensional electrons is maintained at a uniform distance of 10 nanometers from a sheet of 2-dimensional holes. Electrical current can be passed through each sheet independently. In these bilayer devices, the attractive (interlayer) interaction between the electrons and holes is stronger than the repulsive intralayer interactions between electrons or holes in the same layer. This is a new regime in semiconductors that has been envisioned for a few decades but only recently realised. These devices are at the very frontier of what is technologically possible today - they require a confluence of highly developed Molecular Beam Epitaxy (MBE), photolithographic processing at micron and submicron level as well as expertise in measurements at millikelvin temperatures.The interaction strength between the electron and hole layers can be directly measured by shaking the particles in one layer and measuring how much the particles in the other layer tends to move in response. The attractive interaction, can lead to bound states of an electron and a hole. Experimentally this may appear as an increased tendency of one layer to move in phase with motions in the other layer. Because the electrons and holes are confined to their respective layers they cannot collapse and annihilate each other. The lowest energy state in such systems may be formed of bound pairs (indirect excitons) analogous to the Hydrogen atom or it may involve a more complex state where the densities of the electrons and holes undergo spontaneous modulations at certain wavevectors. The indirect exciton has an integer spin angular momentum, because its constituent electron and hole are both fermions with half-integer spins. This bound pair behaves like a boson - as all particles with integer spin must. The ground state of a bose gas can be a condensate where a large number of particles are locked into a zero momentum state. This remarkable phenomena known as Bose-Einstein Condensation has been observed in dilute clouds of atoms at few microkelvin temperatures. Quantum mechanics clearly predicts that lighter bosons (like indirect excitons) can undergo a transition to a condensate state at much higher temperatures, easily achievable using liquid Helium rather than laser cooling. A remarkably rich phase diagram of the electron-hole bilayer has been anticipated for decades. Our proposedstudy will give fundamental insights to scattering processes and collective states in bilayer systems as wellas lead to realistic possibilities of achieving a Bose condensate with superfluid like properties in a controlled solid state system.

当两种不同的半导体接触时，它们的导带和价带通常在界面上不连续。带的轮廓可能类似于可以捕获电子和空穴的势阱。这些被捕获的载流子在平行于界面的方向上具有很高的移动性，但在三维空间中被限制在几十纳米范围内。这一能带工程原理催生了硅 MOSFET 和基于砷化镓的高电子迁移率晶体管 (HEMT)，彻底改变了电子学。同时，这些设备开启了二维电子系统的迷人世界。最近的技术进步使得能够制造出二维电子片与二维孔片保持 10 纳米均匀距离的器件。电流可以独立地通过每个片材。在这些双层器件中，电子和空穴之间的吸引（层间）相互作用强于同一层中电子或空穴之间的排斥的层内相互作用。这是半导体领域的一种新机制，几十年来人们一直在设想，但直到最近才实现。这些设备处于当今技术的最前沿 - 它们需要高度发达的分子束外延 (MBE)、微米和亚微米级光刻处理以及毫开尔文温度测量专业知识的融合。通过摇动一层中的粒子并测量另一层中的粒子响应移动的程度，可以直接测量电子层和空穴层。吸引相互作用可以导致电子和空穴的束缚态。实验上，这可能表现为一层与另一层的运动同相移动的趋势增加。因为电子和空穴被限制在各自的层中，所以它们不能坍缩和湮灭彼此。此类系统中的最低能态可能由类似于氢原子的束缚对（间接激子）形成，或者可能涉及更复杂的状态，其中电子和空穴的密度在某些波矢处经历自发调制。间接激子具有整数自旋角动量，因为其组成电子和空穴都是半整数自旋的费米子。这个束缚对的行为就像玻色子——所有具有整数自旋的粒子都必须如此。玻色气体的基态可以是凝结物，其中大量粒子被锁定在零动量状态。这种被称为玻色-爱因斯坦凝聚的显着现象已在几微开尔文温度的稀原子云中观察到。量子力学清楚地预测，较轻的玻色子（如间接激子）可以在更高的温度下转变为凝聚态，这可以使用液氦而不是激光冷却轻松实现。几十年来，人们一直期待电子-空穴双层的非常丰富的相图。我们提出的研究将为双层系统中的散射过程和集体态提供基本见解，并带来在受控固态系统中实现具有超流体性质的玻色凝聚体的现实可能性。

项目成果

Orientation of hole quantum Hall nematic phases in an out-of-plane electric field

面外电场中空穴量子霍尔向列相的取向

• DOI: 10.1103/physrevb.99.195420
• 发表时间: 2019
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Croxall A

A complete laboratory for transport studies of electron-hole interactions in GaAs/AlGaAs systems

GaAs/AlGaAs 系统中电子-空穴相互作用输运研究的完整实验室

• DOI: 10.17863/cam.7563
• 发表时间: 2017
• 作者: Cumis U

Quantised Charge Transport driven by a Surface Acoustic Wave in induced unipolar and bipolar junctions

感应单极和双极结中表面声波驱动的量子化电荷传输

• DOI: 10.48550/arxiv.1910.05082
• 发表时间: 2019
• 作者: Chung Y

Experimental Progress towards Probing the Ground State of an Electron-Hole Bilayer by Low-Temperature Transport

低温输运探测电子-空穴双层基态的实验进展

• DOI: 10.1155/2011/727958
• 发表时间: 2011
• 期刊: Advances in Condensed Matter Physics
• 影响因子: 1.5
• 作者: Das Gupta K

Fabrication and characterization of ambipolar devices on an undoped AlGaAs/GaAs heterostructure

• DOI: 10.1063/1.3673837
• 发表时间: 2012-01-30
• 期刊: APPLIED PHYSICS LETTERS
• 影响因子: 4
• 作者: Chen, J. C. H.;Wang, D. Q.;Hamilton, A. R.
• 通讯作者: Hamilton, A. R.