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

Rare-earth gallates, NdGaO 3 and PrGaO 3 , as substrates lattice-matched to superconducting YBCO thin films are grown using a Czochralski pulling technique. NdGaO 3 was twin-free, while PrGaO 3 was badly twinned. Twinning in PrGaO 3 is presumably due to the first-order phase transition below the melting temperature. On twin-free NdGaO 3 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.