Quantal Heating of 2D Electrons in Crossed Electric and Quantizing Magnetic Fields

* 技术摘要 * 最近对置于量子化磁场中的2D电子进行的实验已经确定了一种新的焦耳加热，这种加热只发生在量子系统中。这种效应在经典系统中是不存在的。量子加热产生了特殊的电子光谱分布，它明显偏离了费米-狄拉克形式。实验表明，即使是微弱的量子加热也会引起对欧姆定律的异常强烈的违反，从而从根本上改变电子输运。过热的电子经历转变成电压不依赖于电流的状态（ZDR状态），同时表现出明显的金属-绝缘体（M-I）转变。这些有趣的现象以及量子加热的一些基本性质还没有被理解和矛盾。该项目致力于探索量子加热，ZDR状态和具有不同量子电子寿命的系统中的表观M-I跃迁的基本性质和限制的实验-调节加热的最基本参数。实验将在一组2D电子系统上进行，这些系统形成在具有不同碳杂质密度的高质量GaAs量子威尔斯中，这些碳杂质控制量子寿命。这项研究将通过采用最先进的实验科学工具来完成：极高质量的导电材料的生长，微和纳米制造，低温实验和复杂的计算机模拟。该项目将支持量子物理和材料研究高级领域的博士生的教育和培训。* 非技术摘要 * 电流加热是一种众所周知的效应，对我们的日常生活有着巨大的影响。除了其积极的实际应用外，加热通常是电路中的不良影响。例如，供暖导致电力线的巨大能量损失，这转化为我们经济的重大资本损失。尽管人们普遍认识到，在一些新型导电材料中，电加热的许多特征非常令人惊讶。最近的实验表明，电流可能不会增加量子导体中的电子温度，量子导体是具有类似原子能谱的材料。 在量子导体中，电流在光谱的某些部分产生异常强烈的电子过热，并引起这些材料的导电性质的巨大变化，这对于应用是有价值的。该项目将进行实验，以探索非常量子加热的基本性质，这是知之甚少和矛盾的。这将通过采用最先进的实验科学工具来实现：极高质量的导电材料的生长，微和纳米制造，量子导体的低温实验和全面的计算机模拟加热。该项目将支持这些先进技术的博士生的教育和培训。

**** TECHNICAL ABSTRACT****Recent experiments on 2D electrons, placed in quantizing magnetic fields, have identified a new kind of Joule's heating, which occurs exclusively in conducting quantum systems. The effect is absent in classical systems. The quantal heating produces peculiar spectral distribution of electrons, which deviates significantly from the Fermi-Dirac form. Experiments show that even a weak quantal heating induces exceptionally strong violation of Ohm's Law, changing radically the electron transport. Overheated electrons undergo a transition into a state in which voltage does not depend on current (ZDR state), demonstrating simultaneously an apparent metal-insulator (M-I) transition. These intriguing phenomena as well as some fundamental properties of the quantal heating are not understood and contradictive. This project pursues experiments probing the fundamental properties and limits of the quantal heating, ZDR state and the apparent M-I transition in systems with different quantum electron lifetime - the most essential parameter regulating the heating. The experiments will be done on a set of 2D electron systems, formed in high quality GaAs quantum wells with different density of carbon impurities, which control the quantum lifetime. The research will be accomplished by employing the most advanced tools of experimental science: growth of conducting materials of exceptionally high quality, micro and nano-fabrication, low temperature experiments and sophisticated computer simulations. This project will support education and training of a PhD student in advanced areas of quantum physics and materials research. ****NON-TECHNICAL ABSTRACT**** Heating by electric current is a broadly known effect, which has a vast impact on our everyday lives. Besides its positive practical applications, heating often is an undesirable effect in electric circuits. For example, heating causes enormous energy losses in power lines, which translate to significant capital losses for our economy. Despite the general understanding, in some novel conducting materials many features of the electric heating are very surprising. Recent experiments indicate that the electric current may not increase electron temperature in quantum conductors, which are materials with an atomic-like energy spectrum. In the quantum conductors the current generates exceptionally strong electron overheating in certain parts of the spectrum and induces enormous variation of conducting properties of these materials, which is valuable for applications. This project will pursue experiments to probe fundamental properties of the extraordinary quantal heating, which are poorly understood and contradictive. This will be accomplished by employing the most advanced tools of experimental science: growth of conducting materials of exceptionally high quality, micro and nano-fabrication, low temperature experiments on quantum conductors and comprehensive computer simulations of the heating. This project will support education and training of a PhD student in these advanced technologies.