Third sound in superfluid helium film on a quasiperiodic substrate

Abstract

IR spectra of a natural CaTiO₃ perovskite single-crystal show two absorption bands at 3394 and 3326 cm^?1 which are attributed to structural OH defects. The two bands are weakly pleochroic in a (001) section, but show a more distinct anisotropic behaviour in (110) with a stronger component of absorption perpendicular to [001]. A plausible model for the mode of OH incorporation on a preferred atomic position is derivable under the assumption of vacancies in the Ca-lattice. An OH dipole direction roughly pointing along [110] with O2 oxygens acting as donor oxygens is consistent with the measured pleochroic scheme of the bands.