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September 1, 2004


Dr. Junichiro Kono
Department of Electrical Engineering
Rice University
"Controlling the Metallicity of Carbon Nanotubes through the Aharonov-Bohm Phase"

Abstract.  Single-walled carbon nanotubes, tubular crystals of sp2-bonded carbon atoms that are just one atom thick, come in different varieties, each with a subtle difference in structure and properties – some of them are metals and others are semiconductors.  However, their basic electronic properties can change when they are placed inside a magnetic field.  Specifically, we found that the band gaps of semiconducting nanotubes shrank steadily in the presence of a strong magnetic field; in even stronger fields, we expect the gap to disappear altogether, causing the semiconducting nanotubes to transform into metals.  This behavior is unique among known materials, but it is consistent with theoretical predictions based on the so-called Aharonov-Bohm phase.  Although the Aharonov-Bohm effect itself has been observed in other physical systems, this is the first case where the effect interferes with the Bloch theorem to directly modify the band structure.  This arises from the fact that nanotubes are crystals with well defined lattice periodicity.  Implications for future research and applications based on this effect will be discussed. Reference:  S. Zaric, G. N. Ostojic, J. Kono, J. Shaver, V. C. Moore, M. S. Strano, R. H. Hauge, R. E. Smalley, and X. Wei, “Optical Signatures of the Aharonov-Bohm Phase in Single-Walled Carbon Nanotubes,” Science 304, 1129 (2004). 

Vanderbilt University