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Collective excitations and the nature of Mott transition in undoped gapped graphene

Jafari, S. A ; Sharif University of Technology

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  1. Type of Document: Article
  2. DOI: 10.1088/0953-8984/24/30/305601
  3. Abstract:
  4. The particle-hole continuum (PHC) for massive Dirac fermions provides an unprecedented opportunity for the formation of two collective split-off states, one in the singlet and the other in the triplet (spin-1) channel, when the short-range interactions are added to the undoped system. Both states are close in energy and are separated from the continuum of free particle-hole excitations by an energy scale of the order of the gap parameter Δ. They both disperse linearly with two different velocities, reminiscent of spin-charge separation in Luttinger liquids. When the strength of Hubbard interactions is stronger than a critical value, the velocity of singlet excitation, which we interpret as a charge composite boson, becomes zero and renders the system a Mott insulator. Beyond this critical point the low-energy sector is left with a linearly dispersing triplet mode - a characteristic of a Mott insulator. The velocity of the triplet mode at the Mott criticality is twice the velocity of the underlying Dirac fermions. The phase transition line in the space of U and Δ is in qualitative agreement with our previous dynamical mean field theory calculations
  5. Keywords:
  6. Collective excitations ; Composite bosons ; Critical points ; Critical value ; Dirac fermions ; Dynamical mean-field theory ; Energy scale ; Gap parameter ; Hubbard interaction ; Low energies ; Luttinger liquids ; Mott insulators ; Mott transitions ; Short range interactions ; Spin-charge separation ; Undoped systems ; Graphene ; Mean field theory ; Velocity
  7. Source: Journal of Physics Condensed Matter ; Volume 24, Issue 30 , 2012 ; 09538984 (ISSN)
  8. URL: http://iopscience.iop.org/article/10.1088/0953-8984/24/30/305601/meta;jsessionid=F8456748D14142E49D9AFCC0A26072AB.c3.iopscience.cld.iop.org