Carbon nanotubes as excitonic insulators

DIPC Seminars

Dr. Massimo Rontani, Cnr-Nano, Modena, Italy
Donostia International Physics Center
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Carbon nanotubes as excitonic insulators **Carbon nanotubes as excitonic insulators** Daniele Varsano1, Sandro Sorella2, Davide Sangalli3, Matteo Barborini1, Stefano Corni1, Elisa Molinari1,4, and _Massimo Rontani_ 1 1 _Cnr-Nano, Modena, Italy_ 2 _SISSA & Cnr-Iom Democritos, __Trieste, Italy_ 3 _Cnr-Ism, Roma, Italy_ 4 _FIM, 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.