Polaronic behavior in La_1.2Sr_1.8Mn₂O₇

La_1.2Sr_1.8Mn₂O₇ has been an intriguing candidate for probing electronic correlations due to the concomitant emergence of colossal magneto resistance with its paramagnetic-insulating to ferromagnetic-metallic transition at T_c = 120 K. Experimental evidence has demonstrated the relevance of polarons across the phase transition. In particular, early ARPES studies showed the abrupt formation of a small quasi-particle peak with strong mass renormalization in the metal phase which has been associated with a polaronic metal state. Yet, conflicting results revealing finite quasi particle spectral weight even above T_c and combined ARPES/STM studies showing sensitivity to the cleaved surface cast doubt on the polaronic metal scenario. Here we use resonant inelastic X-ray scattering (RIXS) which is a bulk-sensitive two-photon-probe. In contrast to ARPES which measures the single particle spectral function, RIXS probes collective excitations and is thus especially suitable for the investigation of charge-lattice coupled phenomena. In this presentation, we will discuss the RIXS signatures of polarons in La_1.2Sr_1.8Mn₂O₇.