This Materials World Network/Inter-American Materials Collaboration award supports a joint research and education program between participants in the US, Brazil, and Chile to explore effects of electron correlations in nanoscale or reduced-dimensionality materials: magnetic adatoms and molecules on surfaces, carbon nanotubes and graphene, and quantum dots in semiconductors and other materials. The increasing ability of experiments to probe correlations at the nanometer scale via advances in fabrication methods and local measurement techniques has given rise to a host of new questions about systems long considered understood in the bulk or in ensembles. Correlations between spins, competition between ordering and screening of magnetic impurities, possible quantum phase transitions between different regimes, and effects of decoherence, are all now explorable in experiments. The research is directed to address these issues, which are intrinsically important to basic physics understanding, as well as to possible technological uses in areas ranging from nanomagnetism and information storage to a host of new carbon-based electronic devices, and even quantum information processing by control of the spin degrees of freedom in electronic systems. The goal is to provide physical insights into correlated electron behaviors and to guide experiments to measure novel properties.
Theoretical research is conducted in the US at Ohio University, the University of Florida, and Oakland University; in Brazil at the Pontificia Universidade Catolica do Rio de Janeiro and the Universidade Federal Fluminense; and in Chile at the Universidad Catolica del Norte, the Universidad Tecnica Federico Santa Maria, the Pontificia Universidad Catolica de Chile, and the Universidad de Antofagasta. Groups at these institutions combine their complementary expertise with different theoretical techniques, including the numerical renormalization group and the embedded cluster approximation, that are proven and reliable in treating nontrivial correlated problems. Close communication with experimental groups both inside the collaboration (at the Universidade Federal de Minas Gerais, Brazil) and outside maintain connections with real systems of interest. The project places significant emphasis on training young scientists in the US and Latin America, by engaging them in current research in a highly collaborative and international environment. Students and a postdoctoral fellow learn modern techniques that will provide them with tools for successful careers in science and with skills that will make them highly employable in industry. Junior researchers are brought together with leading experts at two mini-workshops, one held in Brazil, the other in the US. There are also concerted and well-planned efforts to reach a broader audience at the K-12 levels, through a web site with accessible articles on modern nanoscience developments, a program of school visits, and educational videos and attractive images showing research results.
This award is co-funded with the Office of International Science and Engineering.
This international collaborative project studied different aspects of electronic properties in new materials and nanometer-scale systems. The rapid pace of advances in materials synthesis and manipulation creates an ever-growing need for theoretical descriptions of the physical behavior of electrons under a wide range of conditions. The collaboration has studied the behavior of electrons on metallic surfaces and in graphene, carbon nanotubes, and semiconductor heterojunctions: all systems in which reduced spatial dimensionality enhances the effect of electron-electron interactions and strongly affects the properties of these systems. We have further considered the important role of the spin degree of freedom of electrons, which not only opens a host of interesting fundamental questions concerning the particles’ quantum mechanical behavior, but also holds great promise for novel applications in magnetism, electronics ("spintronics"), and quantum information processing and storage. We have found that the subtle competition between different interactions in the aforementioned systems leads to new states of matter with unusual and unexpected properties. In many cases, the collective behavior is reflected in electrical transport and in the optical response to external fields, providing us with valuable insights into the microscopic world, and allowing us to predict properties in new materials or system geometries. For example, we have demonstrated that coupled quantum dots in semiconductors exhibit phase transitions as system parameters are tuned, allowing the study of dramatically different states of matter in a well-controlled environment. We have also demonstrated that consideration of spin-orbit or electron-phonon interactions can drastically change some of these states, giving rise to unique experimental signatures in conductance measurements. Although most of the work completed under this project is of a theoretical nature, our efforts have been guided and inspired by state-of-the-art experiments. We have collaborated closely with experimental groups and these efforts are reflected in joint publications. Our work has also developed and implemented new theoretical approaches, including analytical and numerical techniques, providing us and other researchers with tools to tackle further problems in the future. This project brought together senior investigators, students, and postdoctoral fellows from four different research groups in the US, working in close collaboration not only among themselves but also with prominent researchers in Brazil and Chile who contributed complementary expertise to the enterprise. This project provided unique opportunities for young researchers, who not only learned cutting-edge techniques for tackling a range of problems in condensed matter physics, but also experienced different research philosophies and styles when working with our international partners. Every one of the students who obtained a PhD working on the project has progressed to postdoctoral or faculty positions in the US or elsewhere.
