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Title: Quantum phase transition triggering magnetic bound states in the continuum in graphene
Authors: Kristinsson, Kristinn
Shelykh, Ivan A.
Guessi, L. H.
Marques, Y.
Machado, R. S.
Ricco, L. S.
Figueira, M. S.
de Souza, M.
Seridonio, A. C.
Issue Date: 2015
Source: Guessi, L. H., Marques, Y., Machado, R. S., Kristinsson, K., Ricco, L. S., Shelykh, I. A., et al. (2015). Quantum phase transition triggering magnetic bound states in the continuum in graphene. Physical Review B, 92, 245107-.
Series/Report no.: Physical Review B
Abstract: Graphene hosting a pair of collinear adatoms in the phantom atom configuration has density of states vanishing in the vicinity of the Dirac point which can be described in terms of the pseudogap scaling as cube of the energy, Δ∝|ɛ|3, which leads to the appearance of spin-degenerate bound states in the continuum (BICs) [Phys. Rev. B 92, 045409 (2015)]. In the case when adatoms are locally coupled to a single carbon atom the pseudogap scales linearly with energy, which prevents the formation of BICs. Here, we explore the effects of nonlocal coupling characterized by the Fano factor of interference q0, tunable by changing the slope of the Dirac cones in the graphene band structure. We demonstrate that three distinct regimes can be identified: (i) for q0<qc1 (critical point) a mixed pseudogap Δ∝|ɛ|,|ɛ|2 appears yielding a phase with spin-degenerate BICs; (ii) near q0=qc1 when Δ∝|ɛ|2 the system undergoes a quantum phase transition (QPT) in which the new phase is characterized by magnetic BICs, and (iii) at a second critical value q0>qc2 the cubic scaling of the pseudogap with energy Δ∝|ɛ|3 characteristic to the phantom atom configuration is restored and the phase with nonmagnetic BICs is recovered. The phase with magnetic BICs can be described in terms of an effective intrinsic exchange field of ferromagnetic nature between the adatoms mediated by graphene monolayer. We thus propose a new type of QPT resulting from the competition between two ground states, respectively characterized by spin-degenerate and magnetic BICs.
ISSN: 1098-0121
DOI: 10.1103/PhysRevB.92.245107
Schools: School of Physical and Mathematical Sciences 
Rights: © 2015 American Physical Society. This paper was published in Physical Review B and is made available as an electronic reprint (preprint) with permission of American Physical Society. The published version is available at: []. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.
Fulltext Permission: open
Fulltext Availability: With Fulltext
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