CWRU Physics Faculty
Walter R. Lambrecht
Professor of Physics
Lic. Sc., University of Gent (1977)
Dr. Sc., University of Gent (1980)
Theory of Materials
web-site: Electronic Structure Group Home Page
In my research group we try to view the world through Schrödinger's equation, or rather the density functional theory Kohn-Sham equations. Almost all properties of a material can ultimately be reduced to the underlying electronic structure. Over the years, I have worked on a variety of materials, from metallic alloys to wide-band gap semiconductors and exotic materials, such as rare-earth compounds. Starting from the electronic band structures, we study optical transitions, magnetic properties, vibrations, cohesive and elastic properties. Some of our present interest are:
Spintronics: The main idea of spintronics is to manipulate both the spin and charge of the electrons. Spin leads to magnetism and our main effort is to study the origin of magnetic exchange interactions in semiconductors doped with transition metal and rare earth ions. In practice, these also interact with native point defects, so we are also strongly interested in the development of better methods to study point defects in crystals. We focus on nitride semiconductors and closely related transition metal and rare-earth nitrides. The interesting properties of these materials derive from the strong correlations of f and d electrons. With NSF funding through a Materials World Network grant we enjoy a collaboration with a group at the MacDiarmid Institute in New Zealand and with Boston University to study these fascinating materials, combining synchrotron based spectroscopies with theoretical modeling.
Wide band gap semiconductors: We are interested in the properties of a novel class of nitride wide band gap semiconductors, the II-IV-N2 semiconductors, such as ZnGeN2. These materials share a lot of their properties with the much better known GaN, which led to such technological developments as blue lasers and white LED based solid state lighting. However, they offer new ways of band structure engineering. We are collaborating with Kathleen Kash's group who is growing these materials in characterizing and predicting their fundamental properties, such as electronic energy bands, piezo electricity, phonons. We also continue some work on ZnO and related materials, another promising opto-electronic material.
To make these studies possible, we need to keep developing our computational tools. Our group in particular uses the linearize muffin-tin orbital method, which was developed originally by O. K. Andersen at the Max- Planck Institute in Stuttgart. We closely collaborate with one of the main program developers, Mark van Schilgaarde at Arizona State University. This gives us access to the most recent developments, such as the quasiparticle self-consistent GW method, non-collinear magnetic calculations, and so on. We contributed to the LSDA+U implementation in that code and the calculation of optical properties and most recently resonant x-ray emission spectroscopy.