Citation of the 2014 ( the 2nd ) Nishina Asia Award“The elucidation of electronic properties of monolayer and bilayer graphene”
by Professor ZHANG, Yuanbo
Graphite consists of a stack of honeycomb lattice sheets of carbon andconstitutes a quasi-two-dimensional semimetal containing low density
electrons and holes. A single atomic layer of graphite, called graphene, is aunique two-dimensional (2D) system in which massless Dirac electrons
obeying the relativistic Dirac equation are realized. Andre Geim andKonstantin Novoselov succeeded in making micrometer-size graphenesamples, by rubbing graphite flakes onto oxidized silicon substrates, andmeasuring their unique electronic properties. Geim and Novoselov wereawarded Nobel Prize in Physics for their accomplishment.
Yuanbo Zhang, who was a graduate student in Professor Philip Kim’s groupat Colombia University at that time, vigorously worked on graphene. Thepaper [1] reporting the quantum Hall effect (QHE) in graphene waspublished in the same issue of Nature as another paper by Novoselov andGeim reporting essentially the same result. This paper beautifully
elucidated a peculiar QHE characteristic of Dirac electrons in monolayer
graphene that fundamentally differed from the ordinary QHE observed instandard 2D electron systems such as those in GaAs/AlGaAs
heterostructures. This monumental paper, cited more than 5000 times, isestablished as one of the “classics” in graphene research.
After getting PhD, Dr. Zhang joined Professor Zettl’s group at University ofCalifornia, Berkeley as a postdoc and extended his research on graphene.
Electrons in bilayer graphene, unlike monolayer graphene, have non-zeromass. It was theoretically predicted that the energy gap of bilayer graphenevanishes for the case of symmetric bilayer, while a layer asymmetry opens
up a gap. Dr. Zhang verified that the band gap of bilayer graphene can bechanged over a wide range by an electric field applied normal to the layerand demonstrated the potential application of the bilayer system as atunable detector in the infrared range [2]. He also studied local electronic
state of monolayer graphene using STM, and has shown that the spatial
charge fluctuation, which influences the scattering of Dirac electrons,
originates from charged impurities [3].
Besides these representative accomplishments, Dr. Zhang has coauthoreda number of papers which have been cited hundreds of times. His immense
contribution to the graphene research deserves the Nishina Asia Award.
In 2010, Dr. Zhang was appointed to professorship at the Physics
Department, Fudan University, and started to set up his own research groupin active pursuit of novel atomic layer systems. Prof. Zhang is now producing
steady research outputs, including recent results of atomic layer black
phosphor system, and has a highly promising future.
References1. Y.Zhang, Y.-W.Tan. H.L.Stormer, P.Kim, “Experimental Observation of Quantum
Hall Effect and Berry’s Phase in Graphene”, Nature 438, 201 (2005).
2. Y.Zhang, T.-T. Tang, C. Girit, Z. Hao, M.C. Martin, A. Zettl, M.F. Crommie, Y.R. Shenand F. Wang, “Direct Observation of a Widely tunable Bandgap in Bilayer Graphene”.
Nature 459, 820 (2009).
3. Y.Zhang, V.W. Brar, C.Girit, A. Zettl and M.F. Crommie, “Origin of Spatial Charge
Inhomogeneity in Graphene” Nature Physics 5, 722-726 (2009).