This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Two-dimensional (2D) electron systems, systems where the motion of the electrons is confined to a plane, i.e. 2D, are not only relevant to advanced microelectronic and optoelectronic devices, but also important platforms in the study of electrons in reduced dimensions. In the past few decades, 2D electron systems based on semiconductor nano-scale structures (quantum wells) have revealed a plethora of remarkable phenomena which have led to many discoveries and subsequently a deeper understanding of various quantum states of matter. A current focal point in 2D electron physics research is the study of how the strong Coulomb interaction between electrons influences the system?s electronic properties. Conventional wisdom based on weak Coulomb interaction asserts that all 2D electron systems are insulators as long as there are impurities in the sample. However, recent experiments have shown that 2D electrons can show a puzzling metal-like state if the Coulomb interaction between electrons is strong. This project will employ thermodynamic and tunneling experiments as spectroscopic tools to elucidate the nature of 2D electron systems in the metallic phase. The scientific results obtained will shed new light on the long standing problems of the puzzling metallic phase and metal-to-insulator transition in 2D electrons. In addition, this research will advance understanding of current questions of great interest, such as what happens to the properties of a material when the electrons? motions are strongly correlated with each other. Through educating and training students, this project will strengthen the nation?s workforce in science and technology. This project will support a full time graduate student towards his/her PhD degree and will also train part time undergraduate students. Graduate and undergraduate students will gain laboratory skills that will be excellent preparation for them to continue toward career in both academia and industry.
The metal-insulator transition (MIT) in two dimensions (2D) is a long- standing unsolved problem at the heart of condensed matter physics, as a 2D metallic state challenges the celebrated scaling theory of localization which asserts that all disordered 2D Fermion systems are localized (insulating) at zero magnetic field. Although more than ten years have passed since the first report of a possible 2D MIT in silicon, there is still no consensus on the underlying mechanism of the metallic-like transport behavior in strongly correlated 2D Fermion systems. This project will tackle the problem on new fronts by focusing on spectroscopic studies in the metallic state. Both thermodynamic and tunneling density of states (DOS) experiments will be performed in addition to the conventional transport measurements to study the 2D metallic state in p-type gallium arsenide quantum wells with high carrier mobility. Through investigating the compressibility and energy-resolved tunneling DOS spectra of the 2D metal, this project will lead to new insights to some widely debated questions: e.g. is the ?2D metallic state? a new state of matter? If so, what kind of electronic state of matter is it? This project will also support a full time graduate student and several part time undergraduate researchers. The experimental work to be implemented by the graduate and undergraduate students will provide them a comprehensive education and training in different research areas including low-temperature physics, nanofabrication and low-noise experimentation. This training will motivate and prepare the students for scientific careers in both academia and industry.
