Excitonic effects in two-dimensional massless Dirac fermions
Abstract
We study excitonic effects in two-dimensional massless Dirac fermions with Coulomb interactions by solving the ladder approximation to the Bethe-Salpeter equation. It is found that the general four-leg vertex has a power-law behavior with the exponent going from real to complex as the coupling constant is increased. This change of behavior is manifested in the antisymmetric response, which displays power-law behavior at small wave vectors reminiscent of a critical state, and a change in this power law from real to complex that is accompanied by poles in the response function for finite-size systems, suggesting a phase transition for strong enough interactions. The density-density response is also calculated, for which no critical behavior is found. We demonstrate that exciton correlations enhance the cusp in the irreducible polarizability at 2kF, leading to a strong increase in the amplitude of Friedel oscillations around a charged impurity.
- Publication:
-
Physical Review B
- Pub Date:
- January 2011
- DOI:
- 10.1103/PhysRevB.83.035404
- arXiv:
- arXiv:1010.0695
- Bibcode:
- 2011PhRvB..83c5404W
- Keywords:
-
- 71.45.Gm;
- 73.22.Pr;
- 71.10.-w;
- Exchange correlation dielectric and magnetic response functions plasmons;
- Theories and models of many-electron systems;
- Condensed Matter - Strongly Correlated Electrons
- E-Print:
- 16 pages, 18 figures