Electrical Transport in Thin Film Nanostructures Hanno H. Weitering, The University of Tennessee, DMR Understanding and control of electrical conductivity through nanostructures requires extensive control of their structure and morphology, which can sometimes be achieved via self assembly. Strong quantum-mechanical size effects enable the formation or self assembly of lead (Pb) atoms into atomically smooth thin films. The resulting films are only a few atom layers thick, while their lateral dimensions easily exceed several millimeters. These films present an ideal geometry for exploring superconductivity at the nanoscale. Even the thinnest Pb films (6 atom layers) are extraordinarily robust superconductors with a superconducting critical temperature T C slightly below that of bulk Pb. The thermodynamic parameters T C and upper critical field H c2 are completely dictated by the physical dimensions and boundary properties of the film. These films support macroscopic critical state screening currents of the order of 4 MA/cm 2 which is about 10% of the theoretical depairing current density. The remarkable robustness of the critical state in reduced dimensions can be quantitatively understood from the known atomic geometry of “quantum growth defects” that are unique for Pb. These quantum defects are strong pinning centers of magnetic flux lines (“vortices”), leading to robust superconductivity. Quantum growth defects in a nine monolayer Pb film showing two-atom layer tall mesas (left) and two-atom layer deep voids (right) in films with tiny excess or shortage of Pb, respectively. Quantum mesas produce a “soft” hysteresis loop (lower left), while quantum voids produce a “hard” hysteresis loop (lower right). The latter indicates strong vortex pinning. Nature Physics 2, (2006)

Electrical Transport in Thin Film Nanostructures Hanno H. Weitering, The University of Tennessee, DMR Education: Two graduate students (Murat Özer and Eun Ju Moon) and one postdoc (Jiandong Guo) were supported by this award. Murat Özer was first author on a paper in the March 2006 issue of Nature Physics showing that films only a few atom layers thick can carry enormous supercurrents—defying theories that superconductivity is typically weak at the nanoscale. For this work, he won the prestigious Nottingham Prize for best student presentation at the 2006 Physical Electronics Conference at Princeton University. He also received the University Chancellor’s Citation for Professional Promise and a Paul H. Stelson Research Fellowship from the Physics Department. Murat Özer received his Ph.D. degree at UT in the summer of He is currently postdoc at the University of Texas in Austin. Dr. Jiandong Guo pioneered optical studies of thin film nanostructures. He left the group in October 2005 to become a junior physics professor at the Chinese Academy of Sciences in Beijing. Eun Ju Moon began her thesis research in January She has build dedicated measurement equipment for in-situ studies of quantum transport in thin film nanostructures and is continuing her Ph.D. dissertation research. Societal Impact: Nanoscience represents a very promising avenue for future innovations in e.g. the physical sciences, medicine, and information technology. A key requirement for making functional nanodevices is the ability to acquire perfect control of their structure and morphology. A viable way to accomplish this is to exploit quantum mechanical laws while tuning and assembling nano structures. This work represents an important case-study, showing: (1) how quantum mechanics can be used to control the structure and morphology of thin film nanostructures at the atomic level, and (2) how the “quantum engineered morphology” of thin films relates to one of their most appealing functionalities, namely dissipation-free electrical conductivity or “superconductivity.”