Theory of quantum materials

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Classical phase transition such as boiling water to freezing ice occurs via change of temperature. Quantum phase transition at nearly zero temperature occurs by tuning quantum parameters such as pressure, magentic field, and chemical compositions. The transition between different phases of matter is described  by a change of complex ground state of a many-body system due to quantum fluctuations. Materials where such a quantum many-body effect (which determines its complex-valued ground state wavefunction) manifests itself and leads to unexpected phenomena are called quantum materials. One of novel yet unresolved behavior in quantum materials is the so-called non-Fermi liquid behavior observed in a wide range of temperature. The Fermi-liquid theory based on the notion that electron retains its integrity as a quasiparticle excitations about the many body ground state, fails to describe physical properties of these materials. I propose to investigate the origin of non-Fermi liquid behaviors in quantum materials such as transition-metal oxide materials including high temperature superconductors, heavy fermion materials, and magnetic materials. In particular, I am interested in theoretical understanding of inhomogeneous or anisotropic quantum systems, and its physical properties related to non-Fermi liquid behaviors. I will also study non-Fermi liquid behaviors observed near the quantum phase transition in magnetic materials.