  The experimental results hinting at the room temperature and ambient pressure
superconductivity and magnetic levitation in LK-99 attracted an unprecedented
interest. While attempts of other teams to reproduce the reported observations
on similar samples failed so far, it seems worthwhile to try building a
theoretical model that would explain the ensemble of the available data. One of
important features that needs to be explained is an apparent contradiction
between an extremely high critical temperature Tc and rather modest critical
magnetic field Bc and critical current jc reported for LK-99. We show
theoretically, that these data may be quantitatively reproduced assuming the
interplay between exciton- and phonon-induced superconductivity, while the
conventional BCS or Brinkman-Rice-Bardeen-Cooper-Schriefer (BR-BCS) mechanisms
would result in a much higher Bc for the same Tc.
