Electronic Transport and Possible Superconductivity at Van Hove Singularities in Carbon Nanotubes.
Van Hove singularities (VHSs) are a hallmark of reduced dimensionality, leading to a divergent density of states in one and two dimensions and predictions of new electronic properties when the Fermi energy is close to these divergences. In carbon nanotubes, VHSs mark the onset of new subbands. They are elusive in standard electronic transport characterization measurements because they do not typically appear as notable features and therefore their effect on the nanotube conductance is largely unexplored. Here we report conductance measurements of carbon nanotubes where VHSs are clearly revealed by interference patterns of the electronic wave functions, showing both a sharp increase of quantum capacitance, and a sharp reduction of energy level spacing, consistent with an upsurge of density of states. At VHSs, we also measure an anomalous increase of conductance below a temperature of about 30 K. We argue that this transport feature is consistent with the formation of Cooper pairs in the nanotube.
Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States.
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Y
Yang
Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States.
G
G
Fedorov
Department of Physics and Astronomy, Northwestern University , Evanston, Illinois 60208, United States.
S E
SE
Shafranjuk
Kavli Institute of Nanoscience, Delft University of Technology , 2600 GA Delft, The Netherlands.|Laboratory for Quantum Limited Devices, Physics Department, Moscow State Pedagogical University , 29 Malaya Pirogovskaya Street, Moscow, 119992, Russia.
T M
TM
Klapwijk
Kavli Institute of Nanoscience, Delft University of Technology , 2600 GA Delft, The Netherlands.
B K
BK
Cooper
Department of Physics, CNAM, and JQI , University of Maryland , College Park, Maryland 20742, United States.
R M
RM
Lewis
Department of Physics, CNAM, and JQI , University of Maryland , College Park, Maryland 20742, United States.
C J
CJ
Lobb
Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States.
P
P
Barbara
carbon nanotubes; tunable superconductivity; van Hove singularities