U.S.-Austria Cooperative Research on the Nonlinear AC Dynamics of Collective Modes

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This award supports Professor George Gruner of UCLA and a graduate student to collaborate with Dr. Karlheinz Seeger and other of the Ludwig Boltzmann Institute for Solid State Physics and the University of Vienna, Austria. They share an interest in the nonlinear ac response of the charge density wave (CDW) ground state. By combining the experimental techniques available at the two institutions, they will explore a range of nonlinear frequency dependent phenomena of solids. They will extend their previous collaboration on CDW's to the low temperature (or type II) CDW dynamics, which has properties fundamentally different from the high temperature dynamics. In addition, they will begin new studies of the nonlinear ac response of high temperature superconductors, with experiments conducted as the function of both temperature and external magnetic fields. They have previously studied the small amplitude ac response of the high temperature superconductors in the micro- and millimeter wave spectral range. This work, which will be continued, is essential in interpreting nonlinear response. Austrian scientists will come to UCLA to conduct the small amplitude (low field) ac response experiments on various single crystal and thin film specimens. The same specimens will then be investigated for ac harmonic mixing at the Ludwig Boltzmann Institute in Vienna. High temperature superconductivity is the focus of very great current interest. Charge density wave research is also a very active area in solid state physics. For both charge density waves and the superconductors in the vortex state, certain responses are fundamentally determined by lattice irregularities. Thus there are significant variations from specimen to specimen, and the same key set of responses must be measured on each specimen. The collaborating U.S. and Austrian research groups bring a unique combination of capabilities to bear on these problems. Complementary experimental methods and measurement facilities at the two laboratories allow the comprehensive investigation of linear and nonlinear response phenomena in the micro-and millimeter wave spectral range. The small amplitude ac response can be monitored at UCLA over a substantial spectral range, while the nonlinear ac response is measured at Vienna at selected frequency.