Role of MgB2/Cr2O3 nano-interfaces in photoinduced nonlinear optical treatment of the MgB2 superconducting films

The calculations of the photoinduced nonlinear optical shift with respect to critical temperature for the MgB2 superconducting films (pure and doped by Cr) were performed using the first principle quantum chemical simulations. The principal role of the nano-interfaces between the MgB2 and Cr2O3 was established, and the nano-interfaces have a thickness varying within the 20-30 nm. The latter was done taking into account their long-range ordering additionally aligned by bicolour optical poling. The bicolour poling was performed by the fundamental 10.6 μm laser beam and its doubled frequency coherent second harmonic generation signal. The so formed internal dc-electric field has introduced additional polarization to the media which re-scale the factor of the electron-phonon interaction including the anharmionic one responsible for the occurrence of charge density non-centrosymmetry and the related second order nonlinear optical response. The simulations of the IR induced bicolour treatment were performed both for pure as well as MgB2 superconducting films doped by Cr3+.