Dr. Cheng-Chien Chen [University of Alabama, USA]
Title: Topological Order and Symmetry-Protected Topological Phase: Numerical Studies of Spin Liquids on Kagome and Honeycomb Lattices
Time: 10:00 - 11:00 AM, Friday, July 8, 2016
Place: Conference Room C206, HPSTAR (Beijing)
Host: Dr. Yang Ding
Landau theory of symmetry breaking provides a universal understanding of transition between states characterized by different order parameters. However, there are phases of matter containing "topological order" which is beyond the usual symmetry description. Here I will first discuss the phase diagram of the spin-1/2 kagome Heisenberg model with further-neighbor exchange and Dzyaloshinskii-Moriya interaction . The phase diagram exhibits a great variety of macroscopic behaviors ranging from long-range magnetism to topological spin liquid. I will next discuss a two-dimensional (2D) Hubbard model with spin-1/2 fermions on a decorated honeycomb lattice . Its low-energy effective Hamiltonian is a compass model showing a unique, magnetically disordered ground state that transforms nontrivially under lattice reflection. The corresponding ground state of the Hubbard model is thus a 2D fermionic symmetry-protected topological phase and cannot be connected adiabatically to a free-fermion topological state.
 T. F. Seman et al., arXiv:1508.01523.
 C.-C. Chen et al., arXiv:1603.03439.
Biography of the Speaker:
Dr. Cheng-Chien Chen received his PhD in physics from Stanford University in 2011. Following graduation, he became a postdoctoral scholar at SLAC National Accelerator Laboratory and later an Aneesur Rahman Postdoctoral Fellow at Argonne National Laboratory. Dr. Chen is currently an Assistant Professor in the Department of Physics at the University of Alabama at Birmingham. His research concerns computational condensed matter physics, with a focus on modeling spin and electron dynamics of strongly correlated materials, such as unconventional superconductors, quantum magnets, and interacting topological states of matter.