MilliKelvin Experiments Utilising Vector Magnetic Field

在低温和强磁场的作用下，利用二维电子气已经发现了许多惊人的物理效应，例如量子霍尔效应和分数量子霍尔效应。在这项工作中，我们建议调查的电子性质的半导体纳米结构在毫开尔文温度下的存在下，一个高的磁场时，电子气的平面和字段之间的角度可以改变。这将开辟一个新的物理研究领域，因为场的方向会影响电子系统的不同性质。例如，自旋分裂由总场决定，而波函数受横向于电子气的场分量的影响。如果使用电子气的耦合层，则层间耦合受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的，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个自由电子图像。然而，在载流子浓度较低的情况下，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，在维格纳谁第一次预测这样的现象后，在一维电子形成一个单一的线和维格纳晶体是平凡的情况下，电子寻求一个规则的周期。然而，随着限制减弱，或者电子排斥增加，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，一行分裂成两行或多行，通过跟踪电导值随约束的变化，可以得到能级的移动随约束势的变化。这已经被观察到，我们称这两行作为电子-电子排斥的结果形成的初始维格纳晶格，IWL。对能级运动结果的分析表明，在形成两个单独的行之前，形成了一种杂化状态，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，因此它们每个都“知道”另一个所处的量子状态。现在有人建议研究IWL和磁性修改的混合状态，其中的电子纠缠。在类似的研究中，将研究电子的各种性质，例如当温度导致自旋快速随机旋转时发生的自旋不相干状态，因此它不再是定义的量子参数。通过无序对电子的定位受到磁场的很大影响，磁场可以驱动系统绝缘，或者相反地在低场去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。该设备的灵活性将被应用于新材料的研究，其中表面和体对整体性能的贡献可以通过改变场的方向。表面导电层中的能级分裂将随横向分量而变化，而体性质由总场决定。

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.