The research of our group attempts to bridge condensed matter physics and materials science. We perform first-principles calculations and model calculations to understand emergent phenomena in quantum materials and predicting new physical properties by designing novel complex materials. While we have general interests in material properties, our research focuses on fundamental physics, such as magnetism, superconductivity and topology. Our group has a strong connection to experiments. Clarifying phenomena in existing experiments and stimulating new experiments constitute the core part of our research.
Below are a few important aspects in our research.
Ab Initio Methods
We use ab initio or first-principles methods to solve many-body Schrödinger equation with Coulomb interaction for complex materials. The basic setup for the calculations is chemical composition and crystal structure, with no a priori assumptions. We focus on several important ab initio methods: density functional theory (DFT), density functional perturbation theory (DFPT) and dynamical mean field theory (DMFT). Combining those methods enables us to study electronic, magnetic, electron-phonon and superconducting properties of complex materials.
Transition metal oxides exhibit rich intriguing properties, such as metal-insulator transition, colossal magneto-resistance and high temperature superconductivity. The reason for those diverse phenomena is that different degrees of freedom in complex oxides, such as charge, spin and orbital, are all coupled to each other, leading to many competing phases. Small variations in crystal structure and chemical composition can induce substantial changes in electronic and magnetic properties of transition metal oxides, imposing a great challenge for theoretical calculations but simultaneously providing a great opportunity for tuning their physical properties.
Here 'strong correlation' refers to the collective phenomena that arise from the Coulomb interaction in many-electron systems (for example, solids). The canonical model to describe such 'strong correlation' is the Hubbard model and its extension. We use first-principles calculations to construct an extended (or multi-orbital) Hubbard model for realistic complex materials and approximately solve it using sophisticated many-body techniques (e.g. DFT+DMFT method). Our goal is to understand how to control collective phenomena and engineer physical properties of strongly correlated materials.