The discovery of new quantum materials may lead to a new insight into the physics problems and applications that will benefit society. For instance, the discovery of unconventional superconductors, such as cuprates and Fe-based superconductors, broadened our understanding of superconductors beyond the BCS theory. In addition, superconductors became more suitable for their applications owing to their high transition temperature.
In terms of materials, our current focus is layered materials with an emphasis on, but not limited to, correlated topological materials. With the steady rise of topological materials, the community’s attention is now shifting to strongly correlated topological materials that host a largely unexplored territory from both a theoretical and experimental perspective. For instance, magnetic ordering in MnBi2nTe3n+1 breaks time-reversal symmetry and opens a gap in its topological surface state. Surprisingly, a new crystalline symmetry rises in the ordered state that executes the realization of the axion insulator*. Not only spin degrees of freedom but also interplay among lattice, charge, and orbital degrees of freedom that are ubiquitous in correlated systems can provide rich topological phase diagrams and strong tunability. These studies are important in deepening our understanding of condensed matter physics, as these phenomena cannot be treated by simple perturbation theory.
Vice versa, insight into the underlying physical mechanisms may lead to the discovery of new materials and applications. The most profound way of learning intrinsic physical properties of materials is by identifying its k-space, electronic structure. The electronic structure contains countless information, including carrier density, effective mass, and lifetime. There are several experimental methods to probe electronic structure. Among them, quantum oscillations and ARPES are prevalent techniques. In particular, ARPES is the most direct way of obtaining materials’ electronic structure and so far the most reliable way of realizing topological states.
In order to have a further comprehensive understanding of material systems like complex strongly correlated materials, it is also crucial to map out broad phase spaces via tuning with chemical doping, pressure, field, and strain. Among these, I am very interested in the strain tuning of materials. One of the main advantages of using strain is that it provides control over the symmetry of elastic deformation. Therefore, it can selectively induce desired symmetry changes of the electronic structure or couple to particular electronic orders and their fluctuations.
*Phys. Rev. B 102, 045130 (2020)