Optical Transitions 1S–2P_x between Lowest States of a Shallow Impurity in Graphene Monolayer

The binding energy of the ground and first excited states of a hydrogen-like impurity electron in monolayer graphene is studied by a variational approach. It is shown that the binding energies of the impurity electron can be tuned by changing the value of the gap and the effective fine structure constant. An analytical expression for the dipole matrix element of the electron transition from the ground to the first excited state of a hydrogen-like impurity in graphene is found.