Bao, Wenzhong and Velasco, Jairo, Jr. and Zhang, Fan and Jing, Lei and Standley, Brian and Smirnov, Dmitry and Bockrath, Marc and MacDonald, Allan H. and Lau, Chun Ning (2012) Evidence for a spontaneous gapped state in ultraclean bilayer graphene. Proceedings of the National Academy of Sciences of the United States of America, 109 (27). pp. 10802-10805. ISSN 0027-8424 http://resolver.caltech.edu/CaltechAUTHORS:20120820-080427165
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At the charge neutrality point, bilayer graphene (BLG) is strongly susceptible to electronic interactions and is expected to undergo a phase transition to a state with spontaneously broken symmetries. By systematically investigating a large number of single-and double-gated BLG devices, we observe a bimodal distribution of minimum conductivities at the charge neutrality point. Although σmin is often approximately 2–3 e^2/h (where e is the electron charge and h is Planck’s constant), it is several orders of magnitude smaller in BLG devices that have both high mobility and low extrinsic doping. The insulating state in the latter samples appears below a transition temperature T_c of approximately 5 K and has a T = 0 energy gap of approximately 3 meV. Transitions between these different states can be tuned by adjusting disorder or carrier density.
|Additional Information:||© 2012 National Academy of Sciences. Contributed by Allan H. MacDonald, April 19, 2012 (sent for review February 1, 2012). Published online before print June 8, 2012. Author contributions: W.B., J.V.J., M.B., and C.N.L. designed research;W.B., J.V.J., L.J., B.S., D.S., and C.N.L. performed research; W.B., J.V.J., F.Z., M.B., A.H.M., and C.N.L. analyzed data; and W.B., J.V.J., F.Z., M.B., A.H.M., and C.N.L. wrote the paper. The authors declare no conflict of interest. W.B., J.V., and F.Z. contributed equally to this work. We thank J. Jung, S. Das Sarma, O. Vafek and Jozsef Cserti for helpful discussions. This work was supported in part by National Science Foundation CAREER DMR/0748910, NSF/1106358, NSF/0926056, ONR N00014-09-1-0724, and the Focus Center for Functional Engineered Nano Architectonics. C.N.L and M.B. acknowledge support by Defense Advanced Research Projects Agency/Defense Micro Electronics Activity H94003-10-2-1003. D.S. acknowledges support by National High Magnetic Field Laboratory UCGP 5068. A.H.M. and F.Z. were supported by Welch Foundation Grant TBF1473 and Department of Energy DE-FG03-02ER45958. The trenches were fabricated at the University of California, Santa Barbara, CA, Nanofabrication facility. Part of this work was performed at the National High Magnetic Field Laboratory supported by NSF/DMR-0654118, the State of Florida, and the Department of Energy.|
|Subject Keywords:||topological states, anomalous hall, spontaneous quantum Hall states, electron–electron interactions, layer antiferromagnets|
|Official Citation:||Wenzhong Bao, Jairo Velasco, Jr., Fan Zhang, Lei Jing, Brian Standley, Dmitry Smirnov, Marc Bockrath, Allan H. MacDonald, and Chun Ning Lau Evidence for a spontaneous gapped state in ultraclean bilayer graphene PNAS 2012 109 (27) 10802-10805; published ahead of print June 8, 2012, doi:10.1073/pnas.1205978109|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||20 Aug 2012 15:43|
|Last Modified:||20 Aug 2012 15:43|
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