Laser heating of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ films in Raman experiments

Magnetron-sputtered and laser-deposited ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ films on MgO(100) substrates are investigated in a Raman setup. We prepare 25-μm-wide microbridges using standard photolithography and argon-ion-beam etching. The change of critical currents of illuminated microbridges is used to determine the spot temperature with high accuracy. The thermal boundary resistance of magnetron-sputtered ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ films on MgO(100) is determined to be ${\mathit{R}}_{\mathrm{bd}}$=(76±9)/${\mathit{T}}^3$ ${\mathrm{K}}^4$ ${\mathrm{cm}}^2$ ${\mathrm{W}}^{\mathrm{-}1}$ and ${\mathit{R}}_{\mathit{b}\mathit{d}}$=(1.7±0.2)×${10}^{\mathrm{-}3}$ K ${\mathrm{cm}}^2$ ${\mathrm{W}}^{\mathrm{-}1}$ for temperatures below and above 35 K, respectively. In order to obtain the spot temperature also Stokes and anti-Stokes Raman spectra are taken. The accuracy of this method, however, is only ±10 K and ±30 K at low and high laser power densities, respectively. At room temperature Raman measurements with increasing laser power densities are performed until oxygen rearrangements and finally oxygen loss in the Cu(1)-O(1) chains are observed. By analyzing the spot temperatures in these measurements and comparing with recent oxygen diffusion experiments we show that both the rearrangement and the oxygen loss are thermally activated processes.