A Comprehensive Experimental Approach to Multifunctional Quantum Materials and their Physical Properties : Geometry and Physics in Condensed Matter

Abstract: This thesis ranges within the vast framework of experimental condensed matter physics. Several different systems, and physical phenomena, are presented here from a structuralist standpoint. In fact, we show how, in solid condensed matter, the underlying arrangement of atoms, the symmetry of their structure, and their mutual interactions, underpin the form and the nature of their collective emergent properties. Our effort in this work was focused on unveiling complex magnetic ground states in newly synthesized materials, as well as in the clarification of unconventional symmetry breaking phenomena in highly debated systems. In all cases, we could understand the physics of such systems only when we elucidated the details, and temperature dependent evolution, of their structures.About the choice of target materials for our investigations, our starting point has not only been fundamental condensed matter physics, but also forward looking towards a sustainable future. Here we considered both the development of energy efficient spintronics and quantum computing, as well as the need for efficient conversion and storage of clean energy. Therefore, this project is concerned with the advanced characterization of novel ”multifunctional” materials, that constitute a unique playground for fundamental scientific research, but also lend themselves to potential novel technical applications. Such materials might indeed display high temperature dynamical properties, which make them suitable for rechargeable batteries and heat conduction applications. At the same time, they are also strongly correlated electron systems at lower temperatures, and their fundamental magnetic and electronic properties are relevant for the development of quantum devices. To explore these properties, extensive experimental studies using large-scale research facilities were employed. In this project, several unique and powerful state-of-the-art high-resolution neutron scattering, X-ray scattering, and muon spin rotation techniques were used.

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