Condensed Matter Physics, Research, Chung, Sung

Our research interest is the theoretical study of strongly correlated condensed matter systems such as realized in high-temperature superconductors, frustrated quantum spins, nano-tubes and graphene, and ultracold atoms trapped in optical lattices. In particular, in recent years we have been developing a novel many-body method, the entanglement perturbation theory (EPT), for calculating the ground states as well as thermodynamic properties of some fundamental models for these strongly correlated condensed matter systems, such as the Heisenberg model, the Hubbard model and the Kondo-lattice model. The success so far is the calculation of spontaneous magnetization and the specific heat of the 3D Ising model [1], the ground state of the 1D Hubbard model [2], and a general description of the ground states in 2 dimensions [3]. Our current efforts include (1) the calculation of the elementary excitations in solids such as spin-wave spectrum in Heisenberg antiferromagnets and fermionic spectrum in Hubbard models, (2) the Kondo impurities and quantum transport through them, (3) thermodynamics as well as dynamics (i.e. density of states) and (4) developments of robust numerical algorithms therein. To put EPT in a word, it is simple, general and exact, and essentially different from the currently available many-body methods such as exact diagonalization, Monte Carlo, numerical renormalization group and various mean field theories. In addition to the EPT, we also pursue a novel path-integral method, the cluster transfer matrix (CTM) [4, 5], for thermodynamics and dynamics (i.e., transport) of Kondo-like systems such as quantum dots, single electron transistors and composites thereof.

- S.G. Chung,
*New method for the 3D Ising model*, Phys. Lett. A 359, 707 (2006). - S.G. Chung,
*New method for the quantum ground states in one dimension*, Phys. Lett. A 361, 396 (2007). - S.G. Chung and K. Ueda,
*Entanglement perturbation theory for the quantum ground states in two dimensions*, Phys. Lett. A 372 , 4845 (2008). - S.G. Chung,
*Cluster transfer matrix method: A novel many-body technique in nanoelectronics*, proceedings of the conference “Formation of Correlations,” June 24-26, Bonn, Germany. Springer monograph "Formation of Correlations" edited by Klaus Morawetz , (2003) pp 39-54. - L. Wang and S.G. Chung,
*Precise implementation of the cluster transfer matrix method in the single electron box*, Phys. Lett. A 372, 2925 (2008).