This grant supports experimental condensed matter physics research aimed at the study of interacting electronic matter in two dimensions. The work focuses on two material systems: gallium arsenide-based semiconductor heterostructures grown by molecular beam epitaxy and graphene, a single atomic layer of carbon atoms. GaAs heterostructures have been intensely studied for several decades, and have yielded a vast trove of important fundamental physics and myriad technical applications. This grant enables further investigation of the remarkable excitonic Bose condensate which is realized in GaAs double quantum wells at high magnetic field, and crucial tests of the concept of excitonic superfluidity will be performed. In contrast to GaAs, graphene is quite new, having been isolated only six years ago. The advent of graphene sparked a firestorm of research owing to both its potential for technological application and its remarkable fundamental physics attributes. The grant enables a new set of experiments on graphene which focus on its thermodynamic and thermoelectric properties. In particular, the energy relaxation rates of the Dirac quasiparticles in graphene will be measured and a novel graphene hot-carrier thermocouple will be fabricated. The research enabled by this grant will contribute greatly to the education of graduate and undergraduate students and a postdoctoral associate.

Nontechnical Abstract

This grant supports basic research on advanced semiconductor materials, and on graphene, a single atomic layer of carbon. The aim is to improve the understanding of how large collections of electrons behave in such materials. The topics of greatest interest are those in which such collective behavior cannot be directly inferred from the detailed understanding of the properties of individual electrons. Such investigations are far from mere academic exercises. One hundred years ago superconductivity was discovered at such low temperatures that practically-minded citizens must have regarded it as a useless curiosity. Nowadays superconductivity is recognized to have revolutionized medical diagnostics by enabling magnetic resonance imaging (MRI). This grant allows experiments on an exotic form of quantum matter, known as an exciton condensate, whose properties resemble those of superconductors. How close the analogy is remains a key question. The grant also support experimentation on the thermal properties of graphene. This new material offers excellent prospects for new discoveries of both fundamental and applied significance. The research funded by this grant is executed by graduate and undergraduate students and a postgraduate associate. Thus this project has a strong educational component and will prepare these young scientists for sophisticated jobs within the Nation's technological base.

Project Report

Modern society depends on all kinds of fancy electronic gadgets, ranging from home computers to smart-phones and GPS navigation aids. Even seemingly mundane appliances like coffee-makers and toasters often have sophisticated electronic brains inside them. In all of these things there are extraordinarily tiny electronic circuits whose development was only made possible after scientists had achieved a deep understanding of how materials conduct electricity and how those materials could be controlled for our purposes. This understanding, deep though it is, is not complete. Nature has many subtle ways of expressing herself and we continue to be confounded and stimulated by them. In essence, the research that has been funded by this NSF grant is about this basic question: What kinds of electrically conducting (and non-conducting) states of matter are there? We've learned over and over again that there are far more possibilities out there than just ordinary metals and ordinary insulators. In the research funded here we have been examining certain rare states of "quantum electronic matter" that somehow seem to be both insulators and conductors at the same time. In our case, these states only appear when a very large magnetic field is applied to the material in question (a man-made layered substance). In particular, the system we have been most interested in conducts along its surface, but not in its interior. Even stranger, while the interior will not allow charge to move through, it is transparent to a strange object known as an exciton. Surprisingly enough, an exciton consists of an electron attached to a "hole", the latter being nothing more than a void between other electrons. These excitons, which carry no net charge, form spontaneously under certain specialized conditions in our laboratory and condense in a fascinating quantum liquid. In our experiments we have explored just what these conditions and how they can be modified. With the excitons condensed, we have performed numerous experiments designed to reveal their various properties. No one has yet developed a concrete application for condensed excitons. But trying to understand them now is not so different from what scientists did long ago when semiconductors were novelties and the transistor had not yet been invented. Beyond these fundamental scientific questions, this NSF grant has been crucial to the professional training of both graduate students and postdoctoral research scientists. Training of this kind is a prerequisite for obtaining a good job in academic, governmental, or industrial laboratories.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Application #
1003080
Program Officer
Guebre X. Tessema
Project Start
Project End
Budget Start
2010-07-15
Budget End
2013-06-30
Support Year
Fiscal Year
2010
Total Cost
$450,000
Indirect Cost
Name
California Institute of Technology
Department
Type
DUNS #
City
Pasadena
State
CA
Country
United States
Zip Code
91125