"Polaron dynamics of the photo-induced hidden metallic phase in La2/3Ca1/3MnO3"
Creating new “hidden” phases that have no analog in thermodynamic equilibrium is becoming increasingly important in condensed matter physics. The use of a femtosecond laser to trigger these “hidden” phase transitions is appealing as some of those phases can be long-lived, with a lifetime of hours or weeks, and reversible with additional external stimuli. However, the investigation of the microscopic interactions in those phases is currently precluded due to the lack of experimental techniques sensitive to multiple degrees of freedom. Here, we develop a technique by combining an ultrafast laser stimulus with ultrahigh-resolution resonant inelastic X-Ray Scattering (RIXS) as the probe. This synergic approach enables us to uncover the excitations of the photoinduced “hidden” phase in La2/3Ca1/3MnO3 (LCMO). Upon ultrafast photoexcitation, the Jahn-Teller distortion is suppressed due to increasing itinerancy of the Mn eg electrons. This renormalizes the polaron and Mn dd excitation energies, leading to a metastable ferromagnetic metallic (FMM) phase that is microscopically distinct compared to the pristine FMM phase. Our findings provide comprehensive understanding behind the photoinduced transition in LCMO. Moreover, the new laser-RIXS approach opens the door to exploring the physics of the photoinduced “hidden” phases in quantum materials with sensitivity to multiple degrees of freedom.