Evidence for a spontaneous gapped state in ultraclean bilayer graphene.
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 σ(min) 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.
Department of Physics and Astronomy, University of California, 900 University Avenue, Riverside, CA 92521, USA.
Wenzhong
W
Bao
Jairo
J
Velasco
Fan
F
Zhang
Lei
L
Jing
Brian
B
Standley
Dmitry
D
Smirnov
Marc
M
Bockrath
Allan H
AH
MacDonald
Chun Ning
CN
Lau
D004553:Electric Conductivity; D004563:Electrochemistry / Q000379:methods; D004581:Electronics / Q000379:methods*; D004583:Electrons; D006108:Graphite / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D008280:Magnetics / Q000379:methods*; D011789:Quantum Theory
D006108:Graphite; D007501:Iron