Theory of quantum materials

经典的相变，如沸水到冰的转变是通过温度的变化发生的。在接近零的温度下，量子相变是通过调节量子参数如压力、磁场和化学成分来实现的。物质在不同相之间的跃迁是由量子涨落引起的多体系统复杂基态的变化来描述的。这种量子多体效应（决定其复值基态波函数）表现出来并导致意外现象的材料称为量子材料。量子材料中一个新的尚未解决的行为是所谓的非费米液体行为，在很宽的温度范围内观察到。费米-液体理论基于电子作为准粒子在多体基态激发时保持其完整性的概念，无法描述这些材料的物理性质。我建议研究量子材料中非费米液体行为的起源，如过渡金属氧化物材料，包括高温超导体，重费米材料和磁性材料。我特别对非均匀或各向异性量子系统的理论理解及其与非费米液体行为相关的物理性质感兴趣。我也将研究在磁性材料的量子相变附近观察到的非费米液体行为。

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.