Yang's research tries to answer a few fundamental questions of broad applications: 1) How electrons interact with each other and impact excited states, such as optical properties; 2) How these fundamental excitations, such as quasiparticles, excitons, plasmons, and phonons, interact and couple with each other to form novel excitations that decide electronic, thermal, and optical properties of materials; 3) How these excited states are modified by quantum confinement of reduced-dimensional structures and how to engineer them for novel transport and energy applications; 4) Understanding electrical and magnetic polarization in materials and how to realize them in reduced-dimensional structures for next-generation transistors and memory devices.