MilliKelvin Experiments Utilising Vector Magnetic Field

许多引人注目的物理效应已经被发现，在低温下使用二维电子气体，在强磁场的存在下，例如整数和分数量子霍尔效应。在这项工作中，我们建议研究半导体纳米结构在毫开尔文温度下，当电子气体与磁场平面之间的角度可以改变时，在高磁场存在下的电子特性。这将开辟一个新的物理研究范围，因为场的方向会影响电子系统的不同性质。例如，自旋分裂是由总场决定的，而波函数受横向于电子气体的场分量的影响。如果使用电子气耦合层，则层间耦合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大的探索。在大多数情况下，半导体中的电子可以被认为是自由电子，它们的能量由它们的总数和它们的有效质量决定，相互排斥只是稍微改变了这种自由电子图像。然而，在载流子浓度较低时，斥力可以支配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，以维格纳第一次预测这种现象。在一维中，电子形成一条单线，而维格纳晶体是电子寻求规则周期性的平凡例子。然而，当约束减弱或电子斥力增加时，当电子试图最大限度地分离时，电子线就有可能扭曲。在此限制中，该行拆分为两个或多个单独的行。通过跟踪约束变化时的电导值，可以得到能级的运动作为约束势的函数。这已经被观察到，我们把由于电子-电子排斥而形成的两行称为早期维格纳晶格（IWL）。对能级运动结果的分析表明，在形成两个单独的行之前，形成了一个杂化状态，其中两个电子在两行之间共享，从而形成了一个扭曲的单行。量子力学表明，以这种方式共享的两个电子必须具有相反的自旋，并且它们可以纠缠在一起，因为它们每个人都“知道”另一个人所处的量子态。现在有人建议研究IWL并对电子纠缠的杂化态进行磁性修饰。在类似的研究中，将研究电子的各种性质，如自旋非相干状态，当温度导致自旋快速和随机旋转时，它不再是一个确定的量子参数。电子的无序定位受到磁场的很大影响，磁场可以驱动系统绝缘，或者相反，在低场中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。该设备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。表面导电层的能级分裂随横向分量的变化而变化，而体积特性则由总场决定。

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.