物理系学术报告       Physics Department Seminar

 

12314:00-15:0012-201

 

 

 

First-Principles calculations of pnictides: Electronic structure, model Hamiltonian, and impurity doping and three-dimensionality of BaFe2As2

 

Professor Hai-Ping Cheng

Department of Physics, University of Florida

 

 

  

 

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.

 

 

Hai-Ping Cheng教授简介:

 

 I.         PERSONAL

            Name:              Hai-Ping Cheng            Sex,  F             Status:  U.S. Citizen

 

II.        EDUCATIONAL BACKGROUND

            Certification of Undergraduate Studies, Fudan University, 1982

            Master of Science (M.Sc.) Northwestern University, 1983

            Doctor of Philosophy (Ph.D.) Northwestern University, June 1988

 

III.       PRESENT POSITION

            Professor, Department of Physics

            2330 NPB, Gainesville FL 32611

            cheng@qtp.ufl.edu

            phone: (352)-392-6256            fax: (352)-392-8722

www.qtp.ufl.edu/~cheng

            Appointment started: August 12, 2005

 

IV.              POSITIONS HELD

 

Visiting Professor, Fudan University, Shanghai China (summer 2007, 2009).

Visiting Professor, University of Paris South, Orsay, France (summer 2004, 2006, 2008)

Director of Research, Laboratoire Aimé Cotton, CNRS, Orsay, France (2002)

Visiting Scientist, Los Alamos National Lab T-10 (July, 2001)

Research Scientist, IBM Zurich Research, Rüschlikon, Switzerland (2000)

Guest scientist, NIST (1996-2001)

Associate Professor of Physics, University of Florida (1999-2005)

            Assistant Professor of Physics, University of Florida (1994-1999)

            Research Scientist II, Georgia Institute of Technology (1992-1994)

            Research Associate, The University of Chicago (1988-1991)