Bilayer, hydrogenated and fluorinated graphene: QED vs SU(2) QCD theory
V. Yu. Irkhin+*, Yu. N. Skryabin+
+M. N. Mikheev Institute of Metal Physics, 620108 Ekaterinburg, Russia
*Ural Federal University, 620002 Ekaterinburg, Russia
Abstract
Motivated by recent experimental and calculational investigations of
bilayer, hydrogenated and fluorinated graphene, we apply the formalisms
of U(1) QED (quantum electrodynamics) and SU(2) QCD (quantum
chromodynamics) theories of strongly correlated state. Unlike
non-bipartite triangular lattice, on bipartite honeycomb lattice
there always exists a monopole that transforms trivially under all the
microscopic symmetries, destabilizing the Dirac spin liquid (DSL), so
that one can continuously tune the DSL state to the state with parent
SU(2) instead of U(1) gauge group. The SU(2) theory describes a
spin-liquid state which is different from usual DSL and is probably unstable
with respect to Neel or valence-bond solid (VBS) phases, except for the
quantum critical point. This point of view means a possibility of VBS
states in graphene systems.