Professor Emeritus, Physics & Astronomy
School of Physical Sciences

Condensed matter theory surface effects in lattice dynamics. Non-linear interactions in magnetic materials and lattice dynamics

www.physics.uci.edu/faculty/wallis.html

Professor Wallis earned his B.S. and M.S. degrees from The George Washington University and his Ph.D. (1952) from The Catholic University of America. He held a postdoctoral position in the Institute for Fluid Dynamics and Applied Mathematics at the University of Maryland for two years and then moved to the Applied Physics Laboratory of The Johns Hopkins University. In 1956 he moved to the Naval Research Laboratory where he became Head of the Semiconductors Branch in 1958. He spent one year at UCI in 1966-67 and then returned to UCI in 1969. He served as Chair of the Department from 1972 to 1975 and from 1980 to 1983.

Professor Wallis's research has involved a number of areas of condensed matter physics. They include surface phenomena, ion transport, and nonlinear phenomena. The present emphasis of the project on surface phenomena is on first-principles calculations of surface phonon dispersion curves in metals. These dispersion curves can be measured experimentally by inelastic electron scattering and by inelastic helium atom scattering. The theoretical interpretation of these curves is complicated by the complex nature of the interatomic interactions in metals. Simple Coulomb or Lennard-Jones interactions are inadequate for metals, so one must calculate the electronic ground state energy, together with the ion-ion interaction energy, gives the vibrational potential energy from which the force constants and dispersion curves can be determined. To handle surfaces, metal slabs are employed. This procedure, which has successfully treated aluminum and sodium, is now being extended to noble metals such as copper and gold. The understanding of ion transport is of particular importance in connection with solid-state batteries in which a lithium ion, for example, moves from a lithium metal anode through an electronically insulating glass to a layered semiconductor cathode. We have already made a number of investigations of lithium ion transport through lithium borate glass. Our future effort will be directed toward the transport of ions across the interface between the glass and the layered semiconductor. The project on nonlinear phenomena concerns nonlinearities in lattice vibrations that arise from anharmonic interactions and optical nonlinearities in magnetic materials. Special emphasis is being placed on the theory of surface phonon line widths and nonreciprocal propagation of nonlinear electromagnetic waves on the surfaces of magnetic systems.

Localized Modes in an Anharmonic Diamond-structure Chain, (with A. Franchini and V. Bortolani), Phys. Rev. B58, 8391 (1998).

Effect of Third-order Dispersion on Nonlinear Magnetostatic Spin Waves in Ferromagnetic Films, (with A. D. Boardman, S. A. Nikitov, N. A. Waby, R. Putnam, and H. M. Mehta), Phys. Rev. B57, 10667 (1998).

Theory of Kink and Domain-wall Excitations in Translationally Invariant Lattices with Quartic Anharmonicity, (with V. Bortolani and A. Franchini), Phys. Rev. B56, 8047 (1997).

Electronic Energy Bands and Lattice Dynamics of Pure and Lithium-Intercalated InSe, (with M. Balkanski and P. Gomes da Costa), Phys. stat. sol. (b) 194, 175 (1996).

Intrinsic Localized Modes in the Bulk and at the Surface of Anharmonic Diatomic Chains, (with A. Franchini and V. Bortolani), Phys. Rev. B53, 5420 (1996).

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https://faculty.uci.edu/profile/?facultyId=2207

Last updated
04/01/2002