Dynamical polarization of graphene in a magnetic field

The one-loop dynamical polarization function of graphene in an external magnetic field is calculated as a function of wave vector and frequency at finite chemical potential, temperature, band gap, and width of Landau levels. The exact analytic result is given in terms of digamma functions and generalized Laguerre polynomials and has the form of a double sum over Landau levels. Various limits (static, clean, etc.) are discussed. The Thomas-Fermi inverse length q(F) of screening of the Coulomb potential is found to be an oscillating function of a magnetic field and a chemical potential. At zero temperature and scattering rate, it vanishes when the Fermi level lies between the Landau levels.