**** 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.
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.
