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Carbon nanotubes as excitonic insulators

Monday, July 17, 2017 - 15:00
Place: 
Donostia International Physics Center
Who: 
Dr. Massimo Rontani, Cnr-Nano, Modena, Italy
Source Name: 
DIPC

Carbon
nanotubes as excitonic insulators

Daniele Varsano1,
Sandro Sorella2, Davide Sangalli3, Matteo Barborini1,
Stefano Corni1, Elisa Molinari1,4, and Massimo Rontani1

1Cnr-Nano, Modena, Italy

2SISSA & Cnr-Iom Democritos, Trieste, Italy

3Cnr-Ism, Roma, Italy

4FIM, University of Modena, Modena, Italy

Fifty years
ago Walter Kohn speculated [1] that a zero-gap semiconductor might be unstable against
the spontaneous generation of excitons—electron-hole pairs bound together by Coulomb
attraction. The reconstructed ground state would then open a gap breaking the symmetry
of the underlying lattice, a genuine consequence of electronic correlations.
Here we show [2] that this 'excitonic insulator' is realized in zero-gap armchair
carbon nanotubes by performing first-principles calculations through many-body
perturbation theory as well as quantum Monte Carlo. The excitonic order
modulates the charge between the two carbon sublattices opening an
experimentally observable gap, which scales as the inverse of the tube radius and
weakly depends on the axial magnetic field. Our findings confute the Luttinger
liquid paradigm for nanotubes and provide tests to experimentally discriminate
between excitonic and Mott insulator.  

References

[1] D.
Sherrington and W. Kohn, Rev. Mod. Phys. 40,
767 (1968).

[2] D.
Varsano, S. Sorella, D. Sangalli, M. Barborini, S. Corni, E. Molinari, and M.
Rontani, arXiv:1703.09235.

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