MAIN RESEARCH TOPICS.

• Spintronic materials : The idea of spintronics is to utilize the spin of the electron as well as the charge in semiconductor devices. It faces materials challenges to merge magnetic materials with semiconductors. Our group focuses on the potential of transition metal and rare-earth compounds, in particular the nitrides. This work is currently sponsored by NSF and ONR. We have started a broad study of the magnetic, structural and electronic properties of the transition metal nitrides. Semiconducting ScN is studied as a potential magnetic semiconductor host. Late transition metal nitrides such as FeN and CoN prefer zincblende structure and are studied as potential spin -injection materials. By alloying them with In, these can become matched to GaN. MnN and CrN are interesting antiferromagnetic materials. In the Mn-N system we also study compounds with other stochiometries such as ferrimagnetic Mn₄N, antiferromagnetic Mn₂N and the ordered defect compound Mn₃N₂. Currently we are working on incorporating calculation of magneto-optical properties in the LMTO codes. We are also developing a LDA+U and screened exchange approach to better deal with narrow band magnetic materials, such as the rare earth compounds.
• Chalcopyrite semiconductors: I-III-VI₂ and II-IV-V₂ compounds such as AgGaTe₂, CdGeAs₂, etc. We are interested in them because of their nonlinear optical properties, which make them useful for frequency conversion, such as second harmonic generation, optical parametric oscillators, etc. which are used in solid state laser systems in the mid-infra red range. Current focus is on point defects in these materials. This work is funded by AFOSR.
• Wide-band-gap semiconductors: Silicon carbide and Group-III nitrides, diamond. These are all useful for high-temperature and high-power electronics and the nitrides are promising for short wavelength electro-optic devices such as LED's and semiconductor laser diodes. Silicon carbide is of interest because of the polytypism. Recent work includes work on stacking fault generation in SiC.
• High-pressure phase transitions We study the transition paths between various crystallographic phases and the effects of anisotropic strain. We have developed a model for the zincblende and wurtzite to rocksalt phase transitions.

METHODOLOGY

We use first-principles computational methods. These are based on the density functional theory in the local density approximation. We use the linearized muffin-tin orbital method as our main computational tool.

PUBLICATIONS

See Lambrecht's CV and list of publications

CURRENT MEMBERS OF THE GROUP:

• Walter Lambrecht, Professor of Physics
• Benjamin Segall, Professor Emeritus of Physics
• Xiaoshu Jiang (graduate student)
• Aditi Herwadkar (graduate student)
• Pavel Lukashev (graduate student)
• Maosheng Miao (Sr. Research Associate)
• Paul Larson (Research Associate)

Group picture in front of the Rockefeller Building