Complex Electron Solids Forming in the Two-dimensional Electron Gas

Purdue University, West Lafayette IN

Investigators

Abstract

Non-technical abstract Stripe-like and bubble-like patterns spontaneously form in numerous physical, chemical, and biological systems. At the origin of these patterns one often finds classical forces with competing long-range and short-range interactions. In electron systems quantum mechanical analogues of these patterns form, but in contrast to their classical counterparts, these quantum mechanical phases are largely unexplored. The PI proposes experimental research and educational activities addressing outstanding questions on the nature of electron solids with stripe-like and bubble-like morphologies that form in a two-dimensional electron sheet. The team will study these electron solids by tuning the electron interactions and by examining quantum mechanical effects. This project offers an excellent opportunity to train graduate and undergraduate students in modern electron physics, semiconductor nanofabrication, cryogenics, and sensitive electronic measurements, skills that are necessary for a successful carrier in science and technology. The PI has involved and will continue to work with students from underrepresented groups. Furthermore, middle and high school students throughout the state of Indiana will be reached through the development of demonstrations and inquiry based activities with the hope of inspiring them to embark on a career in the sciences and engineering. Technical abstract The two-dimensional electron gas is perhaps best known for the integer and fractional quantum Hall effect. Another remarkable property of the two-dimensional electron gas is that, when the disorder level is low enough, charge carriers order into complex electron solids. Such electron solids are abundant in high quality electron gases confined to GaAs/AlGaAs quantum wells. One example for electron solids is the Wigner crystal. However, more complicated solids form when electrons cluster. The electronic bubble phase is due to ordering of these electron clusters on a hexagonal lattice and the so called quantum Hall nematic is a filamentary arrangement of these clusters. In these electron solids elementary quantum mechanics is clearly at play, since they are stabilized as wavefunctions of individual electrons overlap. The team investigates the influence of the structure of the quantum mechanical wavefunction and the effect of the tuning of the electron-electron interaction on the complex electron solids. In addition, the team investigates recently found magnetotransport signatures associated with a crystallization of composite fermions, the emergent particles of the fractional quantum Hall regime. Various transport techniques will be employed. The planned experiments provide insight into the nature of the different types of charge ordered phases forming in the two-dimensional electron gas. Such knowledge contributes to an enhanced understanding of quantum many-body systems and of the electron solids in other condensed matter systems and, in the long term, may lead to possible applications in quantum metrology. Our experiments also offer insight pertaining to the intensely studied fractional quantum Hall states through studies of the phase transitions between the electron solids and the fractional quantum Hall states. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.