Suppression of the "notch effect" in microwave surface resistance in YBa2Cu3O7 films on MgO (100) substrate by deposition of ultra-thin SrTiO3 seed layers

RHEED controlled ultra-thin buffer layers of SrTiO3 have been deposited on (100) MgO by pulsed laser deposition to growth YBaCuO films for microwave applications. A buffer layer with a thickness between 2 and 15 nm, i.e. 5 to 40 unit cells of SrTiO3, is sufficient to expand to more than 60 degrees C the range of deposition temperatures leading to low microwave surface resistance. The Rs values are as good as those obtained on LaAlO3 substrates with a slighly lower magnetic field dependency. The SrTiO3 seed layer induces an oriented epitaxial growth with YBCO [100] // MgO [100] over this range of deposition temperatures.