Exotic correlated phases in oxide two-dimensional electron systems at ultra-low temperature

我们概述了在高质量的氧化镁/氧化锌晶体界面上对二维电子的关联和自旋物理的研究。该系统最近引起了人们的注意，因为它的质量现在可以与最好的半导体材料相媲美，它所展示的分数量子霍尔物理可能有利于基于载流子拓扑性质的量子计算概念。我们的目标是研究它在超低温(T&lt；10mK)下的特性；这是一种仍未被探索的状态。相关物理的一些可能的表现包括铁磁性，即电子自旋自发排列，向列性，粒子排列成空间不均匀的图案，以及超导，电流可以通过而不耗散能量。这些现象已经在其他相关系统中得到了研究，例如高温超导体或重费米子系统。然而，它们在高质量的二维电子系统中的观测仍然难以捉摸，可能有助于解决悬而未决的问题。以前对镁锌锌/氧化锌系统的研究仅限于标准商业低温设备(T&GT；20 MK)中的温度。在这里，我们建议对这种基础设施进行重大改造，以实现T&lt；10MK的超低温。为此，我们计划开发和实施一种在~5MK的温度下包含液化的纯3He的封闭器，样品被浸入其中。连接到样品的热交换器的进一步部署使其能够进入超低温状态。其目标是抑制热波动，这种波动掩盖了系统中存在的脆弱的关联效应。在超低温下，我们计划通过灵敏的传输技术来探索这些样品的电学特性。电阻将作为温度、磁场、电荷密度和晶体方向的函数进行研究。所有这些实验自由度都是揭示电子基态性质的必要旋钮。输运测量的一个关键方面是探索样品的自旋极化，同时利用电场效应改变电荷密度。我们可以通过在磁场中旋转样品来控制这种自旋极化，从而使其能够准确量化。我们将在以前工作的基础上，发现低密度下的增加，表明接近相互作用效应主导的量子临界态的方法。最后，我们设想了通过非平衡共振方法探测电子相互作用效应的补充方法。这将涉及到用电磁光谱的微波区域的辐射来照亮样品，这提供了与半导体中遇到的典型尺度共振的光子能量。探索这些共振的频率相关性将提供定量的光谱结果，以支持在传输过程中进行的观测。

We outline a study of correlation and spin physics of electrons which are confined to two dimensions at a high quality MgZnO/ZnO crystalline interface. This system has attracted attention recently as its quality now rivals that of the best semiconductor materials, and the fractional quantum Hall physics it displays may be beneficial for quantum computation concepts based on topological properties of carriers. We aim to study its characteristics at ultra-low temperatures (T < 10mK); a regime which remains unexplored. Some possible manifestations of correlation physics include ferromagnetism, where electron spins align spontaneously, nematicity, where particles arrange into spatially non-uniform patterns and superconductivity, where current may pass without energy dissipation. These phenomena have been studied in other correlated systems, for example high temperature superconductors or heavy Fermion systems. Their observation in high quality two-dimensional electron systems however remains elusive and may aid in resolving outstanding problems.Previous studies of the MgZnO/ZnO system have been limited to temperatures available in standard commercial cryogenic equipment (T > 20 mK). Here we propose significant modification of such infrastructure as to achieve ultra-low temperatures of T < 10 mK. For this, we plan to develop and implement an enclosure which contains liquefied pure 3He at a temperature of ~ 5 mK, in which the sample is immersed. Further deployment of heat exchangers connected to the sample enables access to the ultra-low temperature regime. The goal is to suppress thermal fluctuations which mask the fragile correlation effects which are present in the system. At ultra-low temperatures we plan to explore the electrical characteristics of these samples through sensitive transport techniques. The resistance will be studied as a function of temperature, magnetic field, charge density and crystal direction. All these experimental degrees of freedom are essential knobs for revealing the nature of the electronic ground state. A key aspect of transport measurements is exploring the spin polarization of the samples while changing the charge density with the electric field effect. We can control this spin polarization by rotating the sample in a magnetic field, allowing its accurate quantification. We will build on previous work which identified an increase at low densities, indicating the approach to a quantum critical state where interaction effects dominate. Finally, we envisage complementary means of probing the electron interaction effects through non-equilibrium resonance methods. This will involve illuminating the sample with radiation in the microwave region of the electromagnetic spectrum, which provides photons of energies in resonance with typical scales encountered in semiconductors. Exploring the frequency dependence of these resonances will provide quantitative spectroscopic results to support observations made in transport.