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

最近对置于量子化磁场中的2D电子进行的实验发现了一种新的焦耳加热，这种加热只发生在导电量子系统中。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，这与费米-狄拉克形式有很大的偏离。实验表明，即使是弱的量子加热也会导致极强的欧姆定律的违反，从根本上改变了电子的传输。过热的电子经历转变成电压不依赖于电流的状态(ZDR状态)，同时显示出明显的金属-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是不被理解和矛盾的。该项目继续进行实验，探索具有不同量子电子寿命的系统中量子加热、ZDR态和表观M-I相变的基本性质和极限--量子电子寿命是调节加热的最基本参数。这些实验将在一组2D电子系统上进行，这些系统形成于高质量的GaAs量子阱中，其中含有不同密度的碳杂质，这些杂质控制着量子寿命。这项研究将通过使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、微米和纳米制造、低温实验和复杂的计算机模拟。该项目将支持在量子物理和材料研究的高级领域对一名博士生的教育和培训。*非技术摘要*电流加热是一种广为人知的效应，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，发热在电路中往往是一种不受欢迎的影响。例如，供暖在输电线上造成了巨大的能源损失，这给我们的经济带来了巨大的资本损失。尽管人们普遍了解，但在一些新型导电材料中，电加热的许多特征是非常令人惊讶的。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，并导致这些材料的导电性能发生巨大变化，这是有应用价值的。这个项目将继续进行实验，以探索超乎寻常的量子加热的基本性质，这一点人们知之甚少，也相互矛盾。这将通过使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、微米和纳米制造、量子导体的低温实验和全面的计算机加热模拟。该项目将支持博士生在这些先进技术方面的教育和培训。

**** 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.