Project Report

One of the most amazing technological advances in the past century is the invention and popularization of the computer. Even small personal devices such as cell phones now contain sophisticated electronics. All of this would not be possible without our understanding of quantum mechanics which governs the very motion of electrons in the various components of our computerized devices. This summer I visited Peking University in Beijing on the EAPSI grant to study the electric transport properties of topological insulators, a class of materials which show promise for future applications in electronic devices. Topological insulators are materials whose behavior is predicted to be protected from weak disorder by the symmetries of the material. The manifestation of this is through the surfaces of the material: although the material is nominally an insulator, the surfaces are conducting due to the topological protection. Ignoring the surfaces, this insulating behavior, called an "insulating bulk," is crucial to the experimental identification of topological insulators. Unfortunately it has proven difficult to develop these materials in the laboratory. For example, bismuth selenide is theoretically predicted to be a topological insulator. However it has defects that add electrons to the system and cause the entirety of the material to become conducting. This washes out any experimental signal of the surface conduction in experiments, hindering further technological developments. In order to get around the conducting bulk problem, it would be useful to have a different way to experimentally identify topological insulators. My work focuses on developing a theoretical prediction of the surface conduction which can be tested in the laboratory and does not rely on the presence of an insulating bulk. One way to move in this direction is to study excitations. In this summer's EAPSI program, I worked with Professor Xie of Peking University to develop a theory of excitons in topological insulators. These are pairs of particles, one electron and one hole, which attract to one another and bind together. A hole is created when an electron vacates a particular quantum state. The hole behaves identically to a particle of opposite charge and same mass as the absent electron. Professor Xie has worked on the theory of excitons in another technologically important material called graphene, which is a single layer of carbon atoms arranged in a hexagonal lattice. The collaboration forged through the EAPSI grant is ongoing as we work towards extending Professor Xie's model to topological insulators. Our work will be one step towards a better understanding of topological insulators. The EAPSI program also provided me the opportunity to meet and collaborate with many other physicists. These connections will prove valuable in furthering the scientific goals of both China and the United States. In addition, the cultural experiences have already proven to be fruitful for myself and my new Chinese friends as they helped me to overcome language and cultural barriers. We have developed a better understanding of the similarities and differences between China and the United States and believe in the strength of the bond between our two countries.

National Science Foundation (NSF)
Office of International and Integrative Activities (IIA)
Application #
Program Officer
Carter Kimsey
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Dasilva Ashley M
University Park
United States
Zip Code