MilliKelvin Experiments Utilising Vector Magnetic Field

利用矢量磁场的毫开尔文实验

• 批准号: EP/K040359/1
• 负责人: Michael Pepper
• 金额: $ 1.07万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FK040359%2F1
• 关键词: MilliKelvin; Experiments; Utilising; Vector; Magnetic

Many striking physical effects have been found using a two dimensional electron gas at low temperatures in the presence of a strong magnetic field, for example the Integer and Fractional Quantum Hall effects. In this work we propose to investigate electronic properties of semiconductor nanostructures at milliKelvin temperatures in the presence of a high magnetic field when the angle between the plane of the electron gas and the field can be altered. This will open up a new range of physical investigations as the direction of the field affects different properties of the electron system. For example, the spin splitting is determined by the total field whereas the wavefunction is affected by the field component transverse to the electron gas. If coupled layers of electron gas are used then the interlayer coupling is affected by the component of field parallel to the plane.This will allow a much greater exploration of a number of effects. In most situations electrons in semiconductors can be regarded as free with their energy determined by their total number and their effective mass with the mutual repulsion only slightly modifying this free electron picture. However at low values of carrier concentration the repulsion can dominate the manner in which the electrons diffuse in the solid, theory has shown that at sufficiently low temperatures the electrons can arrange themselves into a regular array. This is termed a Wigner Crystal, or Wigner Lattice, after Wigner who first predicted such a phenomenon.In one dimension the electrons form a single line and the Wigner Crystal is the trivial case of the electrons seeking a regular periodicity. However, as the confinement weakens, or the electron repulsion increases, so it is possible for the line of electrons to distort as electrons attempt to maximise their separation. In the limit the row splits into two or more separate rows.By following the values of conductance as the confinement is changed so the movement of energy levels can be obtained as a function of confinement potential. This has been observed and we call the two rows formed as a result of the electron-electron repulsion the Incipient Wigner Lattice, IWL. Analysis of the results on the movement of energy levels has shown that prior to the formation of the two separate rows a hybridised state is formed in which two electrons are shared between the two rows such that they form a distorted single row. Quantum Mechanics dictates that two electrons shared in this way must have opposite spins and they can be entangled as a consequence of which they each "know" the quantum state the other is in..It is now proposed to study the IWL and magnetically modify the hybrid state in which the electrons are entangled. In similar studies a variety of properties of electrons will be investigated such as the spin incoherent regime which occurs when temperature causes the spins to rotate rapidly and randomly and so it is no longer a defined quantum parameter. The localisation of electrons by disorder is very much affected by a magnetic field which can drive a system insulating or conversely at low fields remove the interference characteristic of electron waves, This latter effect results in an insulating sample increasing in conductivity.The flexibility of this facility will be applied to the study of new materials where the surface and bulk contributions to the overall properties can be determined by varying the field direction. Energy level splittings in a surface conduction layer will vary as the transverse component whereas the bulk properties are determined by the total field.

在强磁场存在的低温下，使用二维电子气发现了许多引人注目的物理效应，例如整数和分数量子霍尔效应。在这项工作中，我们建议研究毫开尔文温度下在高磁场存在下当电子气平面与磁场之间的角度可以改变时半导体纳米结构的电子特性。由于场的方向影响电子系统的不同特性，这将开辟新的物理研究范围。例如，自旋分裂由总场决定，而波函数则受横向于电子气的场分量的影响。如果使用电子气耦合层，则层间耦合会受到平行于平面的场分量的影响。这将允许对许多效应进行更深入的探索。在大多数情况下，半导体中的电子可以被视为自由电子，其能量由它们的总数和有效质量决定，相互排斥仅稍微改变这个自由电子图。然而，在载流子浓度较低的情况下，排斥力可以主导电子在固体中扩散的方式，理论表明，在足够低的温度下，电子可以将自己排列成规则的阵列。这被称为维格纳晶体或维格纳晶格，以首先预测这种现象的维格纳命名。在一维中，电子形成单线，维格纳晶体是电子寻求规则周期性的微不足道的情况。然而，随着限制的减弱或电子排斥力的增加，当电子试图最大化它们的分离时，电子线可能会扭曲。在极限情况下，该行分成两个或多个单独的行。通过跟踪限制变化时的电导值，可以获得能级的移动作为限制电位的函数。这已经被观察到，我们将由于电子-电子排斥而形成的两行称为初始维格纳晶格，IWL。对能级移动结果的分析表明，在形成两个单独的行之前，形成了杂化状态，其中两个电子在两行之间共享，使得它们形成扭曲的单行。量子力学规定，以这种方式共享的两个电子必须具有相反的自旋，并且它们可以纠缠，因此它们每个“知道”另一个所处的量子态。现在建议研究 IWL 并通过磁力修改电子纠缠的混合状态。在类似的研究中，将研究电子的各种特性，例如当温度导致自旋快速且随机旋转时发生的自旋非相干状态，因此它不再是定义的量子参数。无序电子的定位很大程度上受到磁场的影响，磁场可以驱动系统绝缘，或者相反，在低场下消除电子波的干扰特性，后一种效应导致绝缘样品的电导率增加。该设施的灵活性将应用于新材料的研究，其中表面和体积对整体性能的贡献可以通过改变场方向来确定。表面传导层中的能级分裂将随着横向分量而变化，而体特性则由总场决定。

项目成果

Self-organised fractional quantisation in a hole quantum wire.

空穴量子线中的自组织分数量化。

• DOI: http://dx.10.1088/1361-648x/aaabab
• 发表时间: 2018
• 期刊: an Institute of Physics journal
• 作者: Gul Y

Hall resistance anomalies in the integer and fractional quantum Hall regime

整数和分数量子霍尔体系中的霍尔电阻异常

• DOI: 10.1103/physrevb.102.115306
• 发表时间: 2020-09-15
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: E. Peraticos;Sanjeev Kumar;M. Pepper;A. Siddiki;I. Farrer;D. Ritchie;G. Jones;J. Griffiths
• 通讯作者: J. Griffiths

Thermoelectric and electrical transport in mesoscopic two-dimensional electron gases

介观二维电子气中的热电和电传输

• DOI: http://dx.10.1016/j.crhy.2016.08.012
• 发表时间: 2016
• 期刊: Comptes Rendus Physique
• 影响因子: 1.4
• 作者: Narayan V

Engineering the spin polarization of one-dimensional electrons.

设计一维电子的自旋极化。

• DOI: http://dx.10.1088/1361-648x/aaa7ce
• 发表时间: 2018
• 期刊: an Institute of Physics journal
• 作者: Yan C

Zero-Magnetic Field Fractional Quantum States.

零磁场分数量子态。

• DOI: 10.1103/physrevlett.122.086803
• 发表时间: 2018-10-23
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: Sanjeev Kumar;Sanjeev Kumar;M. Pepper;M. Pepper;S. Holmes;H. Montagu;H. Montagu;Y. Gul;Y. Gul;David A Ritchie;I. Farrer
• 通讯作者: I. Farrer