Condensed Matter and Statistical Physics: "Supercritical Phenomena in Graphene Induced by Charged Impurities"
Starts 27 Jul 2016 11:00
Ends 27 Jul 2016 12:30
Central European Time
Besides being a material with broad spectrum of potential nanotechnology application, graphene has attracted much attention as table-top, testing ground for relativistic quantum mechanics and QED in (2+1)-dimensions. The reason is caused by the fact that quasiparticle dynamics in graphene is relativistic with the coupling constant 300-times smaller than the fine structure constant. In particular, such relativistic and QED effects as vacuum polarizaion, Schwinger pair production, Klein tunneling, Darmstadt effect etc., can be experimentally studied in graphene at almost table-top level. This can be achieved by creating supercritical states in graphene via doping of graphene by charged impurities. They become then planar atoms with relativistic electron dynamics. Such impurities can be engineered by strain as well, or can simply result from adsorbed ions (as was demonstrated by recent experiments). In this talk, discuss supercritical phenomena induced by two charged (Coulomb) impurities by considering both, same and opposite (dipole) signs of charges by presenting detailed introduction to relativistic quantum mechanics, supercritical phenomena and the results on planar relativistic two-center Coulomb problem. In particular, for graphene, we consider the case of two close-by impurities of equal absolute charge. For opposite sign of the charges, this realizes a dipole potential at large distances, while for equal charges one has a symmetric two-impurity potential. For the dipole type impurities, we have established that the dipole potential accommodates towers of infinitely many bound states exhibiting a universal Efimov scaling hierarchy. The dipole moment determines the number of towers, but there is always at least one tower.