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Beyond time constants: Quantifying interactions in correlated materials by complementary ultrafast time-domain approaches

Applicant Dr. Laurenz Rettig
Subject Area Experimental Condensed Matter Physics
Term from 2017 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 329670326
 
Final Report Year 2024

Final Report Abstract

Correlated materials are characterized by a variety of interactions between the elementary degrees of freedom, leading to novel ground states with broken symmetries and often intriguing properties. Goal of this project was to combine several ultrafast time-resolved techniques to quantify these interactions, and unravel their relevance in various complex quantum materials. Charge-Density wave (CDW) materials were chosen as model system for electron-phonon (eph) coupling. In the CDW material TbTe3, we quantified based on time-resolved photoemission and diffraction experiments the transient CDW energy surface, extracted the ultrafast CDW trajectories after a photoinduced phase transition, and demonstrated a transient CDW stabilization due to transiently suppressed lattice fluctuations. Furthermore, the CDW dependence of fundamental interactions such as e-ph and electron-electron coupling was studied on the level of individual bands and modes. In TaS2, coherent control of the transition into a metastable, hidden state was demonstrated. Magnetic interactions and exchange coupling were studied in various antiferromagnetic (AFM) materials by time-resolved photoemission and time-resolved resonant x-ray diffraction. Based on a systematic study of magnetization dynamics in intermetallics of type LnRh2Si2 (Ln=rare earth atom), we uncovered a fundamental relation between angular momentum transfer between AFM sublattices, and interlayer exchange coupling, which also depends sensitively on the conduction electron properties. In addition, the energy flow between the different subsystems was systematically studied. In GdRh2Si2, optical control of the direction of the AFM order as well as excitation of coherent magnons could be demonstrated, allowing us to quantify the magnetic-field dependent magnetic anisotropy energy. Finally, the interaction between spin and lattice degrees of freedom in the Mott insulator NiO has been investigated by time-resolved electron diffraction, highlighting the relevance of exchange striction for a long-lasting nonthermal lattice state. In addition, charge order has been identified as dominant order parameter in the charge- and orbitally-ordered mixed-valence manganite Pr0.5Ca0.5MnO3. Overall, the project has shed light on the microscopic interactions driving complex phase transitions in various quantum materials, with promising results for applications e.g. in future information technology.

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