This proposal aims at using low temperature transport measurements to study correlated electron physics in graphene and nanotubes, which have emerged as nearly ideal one- or two-dimensional electron systems. The first program focus is the study of electron liquids and solids, such as Wigner crystal states in nanotubes and bilayer graphene, and fractional quantum Hall states in the latter. The second focus is novel interaction-driven insulating states, such as the Mott insulating state in carbon nanotubes, with neutral low-energy excitations and unconventionally charged excitations, and the rich spectrum of insulating phases predicted for bilayer graphene, which are expected to exhibit magnetic ordering or spontaneous layer polarization. In addition to deeper understanding of correlated phenomena in nanostructures, the broader impact of this project includes graduate students mentoring, integrating undergraduate education with physics research, e.g. by contributing to the "UCR Undergraduate Research Journal", and mentoring students from under-represented groups. Via participation in UCR's Nanotechnology Outreach Program, the yearly "Summer Physics Academy" at UCR for high school teachers, and supervising local high school interns, this program is expected to positively impact the science and engineering education in local communities.

Nontechnical Abstract

Compared to bulk materials, nanostructured materials often exhibit emergent new properties. For instance, electronic interactions are mostly negligible in bulk materials, but often dominate in one- or two-dimensional (1D or 2D) systems, where electrons' movements become correlated, so much so that the electrons themselves can solidify to form a crystal. Understanding these novel phenomena is not only crucial to the continued miniaturization of electronics, but may also enable new functionalities and devices. This project investigates such novel liquid and solid phases of electrons and interaction-driven insulating states in two archetypal nanostructured systems: graphene, which is a one-atom thick 2D layer of carbon, and carbon nanotubes, which are essentially 1D rolled up tubes of graphene. In addition to deeper understanding of electron behavior in nanostructures and the potential for the development of electronics with novel functionalities, this project's broader impact includes graduate student mentoring, integrating undergraduate education and research, and engaging students from under-represented groups. Via participation in UCR's Nanotechnology Outreach Program, the yearly "Summer Physics Academy" for high school teachers, and supervising local high school interns, this program is expected to positively impact the science and engineering education in local communities.

Project Report

Intellectual Merit: The effect of electron-electron interactions becomes stronger when they are confined to lower dimensional materials such as carbon nanotubes and graphene, which are one- and two- dimensional materials respectively. These materials have emerged as excellent materials with which to study this phenomena and have received a great deal of attention. The Nobel prize was awarded in 2010 to Andre Geim and Konstantin Novoselov for their pioneering experiments on graphene. In our work we performed a number of experiments to investigate novel electronic states that occur in few-layer graphene as a result of electron-electron interactions. We discovered that electron-electron interactions drive bilayer graphene into an insulating state that can be modified by applying perpendicular electric and magnetic fields. In trilayer graphene, we found that interactions modify the properties of the electron system when a magnetic field is applied. In addition to graphene’s electrical properties, we also explored its extraordinary thermal, mechanical and chemical properties. For instance, we found that cleaning the graphene using an annealing process led to better thermal conductivity at low temperatures; graphene can be resonated (much like a timpani drum) and we demonstrated that in small and atomically thin resonators a novel thermal fluctuation mechanism not found in larger resonators determines the quality of the drum resonance tone. In terms of applications, we have developed several novel prototypes, such as using graphene’s native oxide as a gate dielectric to make all-carbon field effect transistors, modifying properties of graphene by attaching metallic complexes or straining it, and making atomic-scale switches. Our works have enabled deeper understanding of fundamental properties of graphene and assisted with the development of next generation graphene-based devices for electronic, mechanical and thermal applications. Broader impact: As a result of our work under this grant, we now have greater knowledge of how electron-electron interactions affect the properties of bilayer and trilayer graphene, which exhibit a rich variety of phases in their electronic states. We also have learned a great deal about graphene’s many other interesting properties such as thermal conductivity and the behavior of electromechanical devices based on graphene or few layer graphene. Our work was integrated with a comprehensive outreach and educational plan. Lau is currently mentoring 9 graduate students and 7 undergraduate students. Moreover, Jairo Velasco Jr. is a Hispanic graduate student who has recently graduated. He is the leading author of a Nature Nantotechnology paper, and recently won the highly prestigious University of California Regents Postdoctoral Fellowship. Of the 7 undergraduates, Mason Gray is a Hispanic student; Kevin Myhro is the second author of a Nano Letters paper, and is now a graduate student in Lau group. David Tran was a co-author of papers published in Nature Physics and Carbon, respectively, and of 3 other manuscripts that have been submitted. He will attend the Physics Ph.D. program at Ohio State University in Fall 2014. In addition, Lau gave a public lecture on nanotechnology and graphene at UCR Palm Desert Center in 2012, which was very well-attended and well-received, and was interviewed by West Texas Public Radio in 2013. Bockrath is mentoring 9 graduate students, including Juan Aguilera who is a Hispanic graduate student. Bockrath also recently mentored Anthony Mendez and Matthew Gonzales, who are Hispanic undergraduate students. Anthony Mendez is a co-author on a Nano Letters paper on graphene FETs with graphite oxide gate dielectric.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Guebre X. Tessema
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University of California Riverside
United States
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