****NON-TECHNICAL ABSTRACT**** This Faculty Early Career Award funds an education and research program aimed at the exploration of new quantum phenomena in graphene nanoelectronic devices. Electrons in graphene, a single-atom thick sheet of graphite, behave very differently from electrons in conventional metals or semiconductors. In particular, their behavior mimics that of ultra-relativistic particles. This results both in many exciting fundamental physics phenomena and also unique electronic properties, such as the world's record electron mobility, with great potential in future nanoelectronic technologies. This project includes a strong interaction between education and research, which will result in excellent materials research training for graduate and undergraduate students. In addition, modern teaching methods, such as computer simulations will be introduced, in the introductory quantum mechanics lectures. These simulations will be translated into Spanish to reach out to the Hispanic community in the US and abroad. Outreach activities, via laboratory visits and public lectures, will have a special focus on science communication to the general public and to the media. Recruiting efforts will contribute to the integration of women, minorities and international students, especially from developing countries, into the scientific community.
This NSF Career award supports a project aimed at understanding the conceptually new behavior of electrons in solids whose effective Hamiltonian is described by the Dirac equation instead of the usual Schrodinger equation. In particular, the research objective is to investigate novel quantum phenomena in graphene, a single-atom thick sheet of graphite, due to its unique relativistic-like electronic structure. Some of these exciting phenomena include the relativistic Josephson effect, Klein tunneling or high-temperature excitonic condensation. To study these phenomena, new nanofabrication methods will be developed to shape graphene into desired nanostructures and the devices will be probed by low-noise variable-temperature transport techniques. This project includes a strong interaction between education and research, which will result in excellent materials research training for graduate and undergraduate students. In addition, modern teaching methods, such as computer simulations will be introduced, in the introductory quantum mechanics lectures. These simulations will be translated into Spanish to reach out to the Hispanic community in the US and abroad. Outreach activities, via laboratory visits and public lectures, will have a special focus on science communication to the general public and to the media. Recruiting efforts will contribute to the integration of women, minorities and international students, especially from developing countries, into the scientific community.
Intellectual Merit The research objective of this proposal was to investigate novel quantum phenomena in graphene due to its unique relativistic-like electronic structure through the fabrication and characterization of ultra-high quality devices. Over the last five years the group has pursued this goal, encountering new surprises as the quality of samples have steadily improved each year. Three results from this prior support are summarized below. One of the most important advances in the study of graphene has been the demonstration of hBN as an ideal substrate material for graphene. After the initial discovery, the Jarillo-Herrero group developed a dry transfer technique which enabled the quick and reliable transfer of graphene and hBN flakes to produce heterostructures devices. One of the avenues made possible by this technique is the study of high-quality ABA-stacked trilayer graphene (TLG), where both massless and massive Dirac subbands coexist. With these devices the Jarillo-Herrero group made the first observation of the quantum Hall effect in ABA-TLG and also observed the crossing of Landau levels that originate from the massless and massive Dirac subbands in TLG. These results were published in Nature Physics 7, 621–625 (2011). Another device geometry enabled by the dry transfer method is a dual-gated structure, where a top gate is insulated from the graphene by an hBN layer. By fabricating very narrow top gates, the device can be used to study quantum interference effects in transport. The Jarillo-Herrero group studied such a geometry in trilayer graphene, where a unique pattern of giant Fabry-Pérot oscillations in the conductance across the narrowly gated junction was observed as the junction parameters were varied. These oscillations are due to conduction through resonant bound states in the junction. Moreover, the PI’s group found that the oscillations could be cloaked classically, by applying a magnetic field, or quantum mechanically, by tuning the pseudospin nature of the wave function on either side of the gate-induced barrier. These results were published in Nature Communications 3, 1239 (2012). Ballistic electronic transport is one of the most prominent phenomena observed in a two dimensional gas that occurs when the electron mean free path is longer than the dimensions of the sample. By using hBN as a substrate, the Jarillo-Herrero group has been able to explore the effects of ballistic transport in graphene devices with multi-terminal contacts. This has allowed the study of transverse magnetic focusing in graphene, where ballistic electrons are deflected by a perpendicular magnetic field and focused to voltage probes at the edge of the sample. By taking advantage of graphene’s gate tunability, the trajectory of the electron focusing can be controlled by modulating the charge density. One of the most striking aspects of these observations is that the electron focusing effects are observable even at room temperature, which reflects the low levels of scattering in the graphene-hBN heterostructure. These results were published in Nature Physics 9, 225-229 (2013). Broader Impact The PI’s broader impact activities have been focused on two major areas: (1) Early involvement of undergraduates, with emphasis on women and underrepresented minorities (URMs), in cutting edge scientific research and (2) science communication to a broad audience. In all these activities, the PI’s efforts have often been geared towards the Hispanic community, given that the PI is a native Spanish speaker. A summary of the PI’s broader impact activities is listed below. Developed a technique for dry transfer of graphene on hBN flakes and hosted several groups to learn the technique. Research mentor of 28 undergraduates through the NSF-funded MIT CMSE-REU and MIT-UROP-MSRP programs, including 10 women and 3 URMs. Research advisor to 9 PhD students, including 2 women and one URM, and 9 postdocs, including one African-American postdoc. Public lecturer at various outreach and international events in and outside MIT: APS 2007 press conference, New York Academy of Sciences Vista Seminar Series, NSF-France funded YESS08 program, Maryland Nanoday 08, MIT Science and Engineering Program for Teachers 08 and 09, MIT IAP Lecture 10. As a result of the APS press conference, the PI hosted 2 journalists to visit the laboratory which wrote three articles on graphene research: one in the New York Times and two in Scientific American. The PI also hosted the PBS-NOVA team for a documentary series on Materials aired Jan 11 ("Making Stuff: Smaller"). Founder and organizer of the Boston Area Carbon Nanoscience (BACON) Meetings, where students and postdocs give talks about their research. The monthly meetings have been running now for over 5 years. The PI translated 2 computer simulation applets from the Physics Education Technology (PhET) group at UC Boulder to Spanish. Introduced interactive teaching methods, such as computer animation applets from the PhET group at UC Boulder, into the teaching of Introductory Quantum Mechanics.
