Ultrafast Raman thermometry for photo-induced superconductivity in YBa₂Cu₃O_6.5

Optical excitation of cuprate superconductors has been reported to induce a transient superconducting state above the critical temperature T_C, evidenced by characteristic features in the time-resolved terahertz reflectivity [1,2]. In YBa₂Cu₃O_6.5, this phenomenon can be observed by resonantly exciting apical oxygen phonon modes at mid-infrared frequencies or by exciting charge carriers in near-IR spectral range [3]. It is thus important to understand the energy transfer processes triggered by these different types of excitations and to characterize heating effects of the crystal lattice.



To this end, we performed time-resolved spontaneous Raman experiments on optically excited YBa₂Cu₃O_6.5. For the different excitation frequencies, we compared the timescales of electron-phonon and phonon-phonon interactions. The temporal evolution of incoherent phonon populations signifies transient changes of the lattice temperature, providing new insight into the non-equilibrium dynamics associated with light-induced superconductivity.