2026/11/20(Fri) 10:30 -12:00 五樓第一會議室 5F, 1st Meeting Room
Title
Laser-induced metastable states in manganites probed by resonant inelastic x-rays scattering
Speaker
Prof. Jonathan Pelliciari (Brookhaven National Laboratory and University of Modena and Reggio Emilia)Abstract
Resonant Inelastic X-ray Scattering (RIXS) is a photon-in photon out technique with momentum and energy resolution particularly amenable for the study of quantum materials. In my seminar I will present our latest work in the development of laser-RIXS to investigate correlated electron systems. La1-xCaxMnO3 is a system displaying a rich phase diagram tunable by doping, epitaxial strain, temperature, and magnetic field. We focus our study on La2/3Ca1/3MnO3 which can be synthesized in thin films as a bulk-like ferromagnetic metal or as a strained antiferromagnetic insulator. The latter is extremely susceptible to photo-induced phase transitions including permanent switching with a lifetime of several hours. Using RIXS at the O-K edge on La2/3Ca1/3MnO3, we map the charge excitations in metallic and insulating materials as a function of temperature. In metallic La2/3Ca1/3MnO3 we observe broad dispersive charge excitations which harden significantly in the antiferromagnetic insulating phase. The energy of the charge excitations tracks with the resistivity as the temperature is increased indicating a polaronic transport regime. The trend of the charge-polaronic energy is confirmed by phenomenological calculations. Using an ultrafast laser in the near-IR (1030nm / 1.2 eV) which was developed at the SIX beamline at Brookhaven National Laboratory, we create a photo-induced metastable transition from antiferromagnetic insulating La2/3Ca1/3MnO3 to a more metallic phase. We measured the in situ resistivity which displayed a persistent decrease upon pumping while our RIXS data exhibit a softening of the charge excitations corroborating a photo-induced transition different from the known bulk ferromagnetic phase. Ultimately, combining the RIXS data with x-ray absorption spectroscopy (XAS) at the O-K edge, we connect the Jahn-Teller distortions with polaronic charge excitations and electron-phonon coupling drawing a phase diagram in the temperature, strain, ultrafast pumping axes.
This work is based on Fan et al. Physical Review X 16, 021018
Language
演講語言 (Language): in English
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