Journal
PHYSICAL REVIEW B
Volume 83, Issue 3, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.83.035404
Keywords
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Funding
- Binational Science Foundation [2008256]
- National Science Foundation (NSF) [DMR-1005035, DMR-0703992]
- Ministerio de Educacion y Ciencia (MEC)-Spain [FIS2009-08744]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1005035] Funding Source: National Science Foundation
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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 2k(F), leading to a strong increase in the amplitude of Friedel oscillations around a charged impurity.
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