Abstract：
First-principle density-functional method has significantly advanced our theoretical understanding of various complex phenomena in condensed matter physics. However, the many-body ground state and the low-energy excitations of strongly correlated systems are beyond the single-particle description of conventional Landau quasi-particle theory. Thus, they cannot be correctly understood within the density-functional theory.
Among the various many-body methods, the dynamical mean-field theory (DMFT) has received much attention due to the power it displays in connection with first-principle method in treating correlated materials. DMFT maps the interacting many-body problems to an interacting impurity problem embedded in a continuous bath, which significantly simplifies the problem. However, the electron self-energy loses its momentum dependence in such a local approximation. By employing the Feynman diagram expansion technique, we proposed a non-local expansion scheme which restores the momentum dependence of the self-energy order by order with the DMFT being the zero-order solution. It is shown that non-local expansion scheme can efficiently describe both short and long-range correlations within significantly reduced computational time, which holds great promise for studying correlated materials with both spatial and dynamical fluctuations.
Biography：
Dr. Gang Li received his bachelor, master and doctor degree in Physics from North-East Normal University (China), Peking University (China) and Bonn University (Germany). He worked as a postdoc research associate at Würzburg University during 2009-2012. Since Sep. 2012 Dr. Gang Li became a joint Principle Investigator in the research unit “SFB-ToCoTronics” hosted at Würzburg Univeristy. After three years, Dr. Gang Li joined the group of Prof. Karsten Held at the Technical University of Vienna and become a subgroup leader. Since 2017, Dr. Gang Li joined ShanghaiTech University and became an assistant professor (tenure-track) and principle investigator.
Dr. Gang Li is interested in the theoretical study of new states of matter in condensed matter systems, including unconventional magnetism, orbital physics, spin-orbit coupling, quantum phase transitions in strongly correlated fermionic systems, and numerical algorithms for two-dimensional quantum systems. Dr. Gang Li has published more than 40 peer-reviewed research articles including Science, Science Advances, Nature Communications, Phys. Rev. Lett., Scientific Report，Phys. Rev. B etc.
Seminar by the NYU-ECNU Institute of Physics at NYU Shanghai