Diffraction studies of quantum materials

• Igor Plokhikh

Diffraction techniques are indispensable tools for resolving crystal and magnetic structures, providing the foundation for understanding the physical properties of functional quantum materials. In this seminar, I will present three case studies from my recent research. The first concerns the kagome superconductor LaRu₃Si₂, which exhibits a cascade of structural phase transitions in addition to superconductivity; variable-temperature X-ray diffraction and (3+N)D crystallography reveal the evolution of its superstructure orders. The second example focuses on the Dirac nodal-line semimetals LnSbTe (Ln = lanthanide), where neutron powder diffraction uncovers multiple competing magnetic phases below the Néel temperature, suggesting complex multi-k ordering not evident from bulk properties. Finally, I will discuss layered nickelates such as La₃Ni₂O₇, recently rediscovered as high-temperature superconductors under pressure, where high-flux neutron diffraction reveals long-range spin-density-wave order and unusual effect of magnetic polymorphism. Together, these studies demonstrate how diffraction approaches can disentangle the intricate interplay of structure, magnetism, and superconductivity in emerging quantum materials.