WHAT ARE QUANTUM MATERIALS, AND WHY DO WE LIKE THEM SO MUCH?
In quantum materials the charge, spin, orbital, and lattice degrees of freedom are intertwined, a tendency which is not exclusive of these systems, but which is strongly enhanced by the strong electron-electron interactions which characterize correlated materials.
Most importantly, the interplay of several degrees of freedom spawns a rich variety of exotic phases emerging out of electronic disorder. Understanding the spatial structure, microscopic symmetry, and kinetic evolution of these phases is crucial to harness these emergent ordered states for technological applications including superconducting energy transport, high-magnetic field applications (MRI), data storage, and quantum computing.
X-ray and Raman scattering are contactless, photon-in/photon-out experimental tools to study and characterize symmetry-breaking phenomena in solids. X-rays detect the signatures of ordered states in momentum space, where Bragg peaks reflect the presence of periodic structures in real space (see below). Raman scattering reveals electronic and structural orders in the frequency (energy) domain, via the feedback of broken symmetries onto lattice vibrations.
Nowadays, the improvements in the spatial and temporal structure of modern laser and x-ray sources will also enable recording ultrahigh-resolution, real-time movies of the ultrafast dynamics of electronic and magnetic phases at the nanoscale.
In addition, photon-in/photon-out light scattering experiments can be used to study of low-dimensional nanomaterials and interfaces that are buried deep below electrodes in a conventional device architecture. This approach paves the way for the study of electronic orders in electrically-tuned low-dimensional materials such as graphene, transition metal dicalchogenides, and oxide thin films and interfaces. The response of these quantum materials under operational conditions (in operando) can be further measured as a function of other control parameters (temperature, magnetic field, etc).
Now, all of this still requires complex materials to study. We perform synthesis of transition metal halide compounds, using solution-based methods (as well as vacuum-based growth, in the future) that can produce crystals of very high quality. These materials exhibit exotic electronic and magnetic states such as orbital order, ferromagnetism, or antiferromagnetism, all of which are closely connected to the crystalline structure and symmetry of these compounds. A largely uncharted territory for these materials is doping, which we plan to explore into in order to reveal a more extended phase diagram and discover possible new electronic phases, in analogy to what occurs in transition metal oxides.
Our group therefore relies on a strong synergy between Synthesis, Spectroscopy, and Scattering to discover and characterize new electronic phases in quantum materials.