Single crystal growth of rare-earth gallates and epitactic growth nature of high-T_c superconducting YBCO thin films on them

Rare-earth gallates, NdGaO₃ and PrGaO₃, as substrates lattice-matched to superconducting YBCO thin films are grown using a Czochralski pulling technique. NdGaO₃ was twin-free, while PrGaO₃ was badly twinned. Twinning in PrGaO₃ is presumably due to the first-order phase transition below the melting temperature. On twin-free NdGaO₃ substrates, the initial growth stages of YBCO ultrathin films are observed by an atomic force microscope (AFM). AFM reveals that the growth mode is of Stranski-Krastanov, showing two-dimensional lateral growth and subsequent three-dimensional island formation, where the growth unit is one or multiples of the c-axis cell length in height.