Supercritical instability in graphene with two charged impurities

We study the supercritical instability in gapped graphene with two charged impurities separated by distance $R$ using the two-dimensional Dirac equation for electron quasiparticles. Attention is paid to a situation when charges of impurities are subcritical, whereas their total charge exceeds a critical one. The critical distance ${R}_{\mathrm{cr}}$ in the system of two charged centers is defined as that at which the electron bound state with the lowest energy reaches the boundary of the lower continuum. A variational calculation of the critical distance ${R}_{\mathrm{cr}}$ separating the supercritical $(R<{R}_{\mathrm{cr}})$ and subcritical $(R>{R}_{\mathrm{cr}})$ regimes is carried out. It is shown that the critical distance ${R}_{\mathrm{cr}}$ increases as the quasiparticle gap decreases. The energy and width of a quasistationary state as functions of the distance between two impurities are derived in the quasiclassical approximation.

Перевод пока недоступен