物理系学术报告 Physics Department Seminar
First-Principles calculations of pnictides: Electronic structure, model Hamiltonian, and impurity doping and three-dimensionality of BaFe2As2
Professor Hai-Ping Cheng
Department of Physics,
In this talk, I survey results and insights gained from first-principles electronic structure calculations on materials that exhibit superconducting behavior at temperatures higher than those characteristic of conventional BCS superconductors. Spcifically, we focus on the border-line itinerant-Mott systems such as the recently discovered 1111 and 122 pnictides.
The ultimate goal of our studies is to correlate Tc with specific material composition using detailed first-principles calculations in conjunction with many-body physics techniques via the critical step of constructing real-materials model Hamiltonians. By manipulating impurity doping, which plays a crucial role in the phase diagrams of high Tc materials, we hope to find guidance for designing candidate systems with Tc higher than ones currently known.
For FeAs-based high-Tc systems, DFT band-structure calculations provide a very good starting point for constructing model Hamiltonians for studies of spin fluctuation and electron pairing mechanisms. Fermi sheets that have been constructed using Wannier transformed Kohn-Sham states have provided critical information for understanding this family of superconducting materials. Analysis of the details of magnetic ordering, density of states, and 2D vs. 3D features in both the 1111 and 122 materials have been valuable in understanding sometimes perplexing experimental findings. Effects of Co impurities have been studied and fully analyzed as well.
Finally, I will discuss persistent challenges related to calculations on the structure of the non-magnetic state Ba1Fe2As2 system using GGA and unsuccessful attempts at using approximations beyond GGA. Both further examination of the underlying physics and development of new approximate functionals are needed.
Name: Hai-Ping Cheng Sex, F Status: U.S. Citizen
II. EDUCATIONAL BACKGROUND
of Undergraduate Studies,
Master of Science (M.Sc.) Northwestern University, 1983
Doctor of Philosophy (Ph.D.) Northwestern University, June 1988
III. PRESENT POSITION
Professor, Department of Physics
phone: (352)-392-6256 fax: (352)-392-8722
Appointment started: August 12, 2005
Director of Research, Laboratoire
Aimé Cotton, CNRS,
Research Scientist, IBM Zurich Research,
Guest scientist, NIST (1996-2001)
Associate Professor of Physics,
Professor of Physics,
Research Scientist II, Georgia Institute of Technology (1992-1994)