Ultrasonic wave propagation and barrier-limited heat flow in thin films of YBa2Cu3O7−x

Abstract

Direct generation and detection of acoustic waveguide modes in thin (<1000 Å) films using the optical-transient-grating method are reported. The upper limit of acoustic damping in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ films was measured to be ∼100 dB/cm for 1-GHz acoustic waves at room temperature. The presence of barrier-limited thermal conductivity into the supporting MgO substrate is demonstrated and a thermal diffusivity of 0.023 ${\mathrm{cm}}^2$/s in the a-b plane at 300 K is measured, which is consistent with previous observations.