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.

当两个不同的半导体接触时，它们的导带和价带通常在界面上是不连续的。能带的轮廓可以类似于可以捕获电子和空穴的势阱。这些被捕获的载流子是高度移动的平行于界面，但被限制在几十纳米的第三维。这一能带工程原理催生了硅MOSFET和砷化镓基高电子迁移率晶体管（HEMT），彻底改变了电子产品。与此同时，这些设备开辟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这样的器件，其中二维电子片与二维孔片保持10纳米的均匀距离。电流可以独立地通过每个片。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的电子或空穴之间的排斥层内相互作用。这是半导体领域的一个新领域，人们已经设想了几十年，但直到最近才实现。这些器件处于当今技术可能性的最前沿-它们需要高度发达的分子束外延（MBE），电子层和空穴层之间的相互作用强度可以通过摇动一层中的粒子并测量另一层中的粒子数量来直接测量。层倾向于移动响应。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运动的趋势增加。因为电子和空穴被限制在它们各自的层中，所以它们不能坍缩和湮灭。这种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，或者它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，因为它的组成电子和空穴都是具有半整数自旋的费米子。这个束缚对的行为就像一个玻色子--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一种凝聚态，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经在几个微开尔文温度下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过渡到凝聚态，这很容易使用液氦而不是激光冷却实现。几十年来，人们一直期待着一个非常丰富的电子-空穴双层相图。我们提出的研究将提供基本的见解，在双层系统中的散射过程和集体状态，以及导致现实的可能性，实现玻色凝聚体与超流体一样的属性在一个受控的固态系统。

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

Quantized 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: 10.1103/physrevb.100.245401
• 发表时间: 2019
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Chung Y