9704020 Sarma This award provides partial support for the development of instrumentation to perform acoustic propagation experiments at the two sites of the National High Magnetic Field Laboratory (Tallahassee, Florida; Los Alamos, New Mexico), by the Division of Materials Research and the Office of Multidisciplinary Activities of the National Science Foundation, and by the University of Wisconsin-Milwaukee. The primary quantities to be measured are the velocity and attenuation of high frequency sound waves, which would be studied as a function of magnetic field and absolute temperature. The materials of interest are primarily highly correlated electron systems; our specific expertise involves the high electron effective mass (heavy fermion) systems, such as the interrnetallic compound UPt3, and the high temperature superconductors. For the heavy ferrnion materials, the interesting physics arises from the fact that the magnetic energy of the spin system, H (where is an effective magnetic moment), can be made comparable to a characteristic f-electron energy describing the heavy fermion state (loosely, a Kondo coherence energy or an f-electron resonance bandwidth). For the high temperature superconductors, an interesting area of study involves observing changes in the elastic constants (as mirrored in the sound velocity) accompanying phase transitions or structural changes in the Abrikosov vortex system and accompanying changes in the dissipation (as mirrored in the acoustic attenuation); an example, though not relevant here, is the two dimensional, liquid-solid melting transition. %%% The Tallahassee and Los Alamos sites focus on steady state and pulsed magnetic fields respectively, which necessitates some differences in the acoustic measurement techniques employed. We will utilize the pulsed-transmission/phase-sensitive-echo- detection approach developed earlier at Milwaukee, Northwestern and elsewhere. Steady state fields permit the use of a low repet ition acoustic pulse rate with relatively long averaging times (via "box car integration") of the received acoustic echo(s). Pulsed acoustics requires very high repetition rates (essentially at the reciprocal of the echo decay rate) and separate sampling and storing of the received echo(s). For this purpose digitizers of the type used at the Los Alamos site will be incorporated in instrumentation purchased from this proposal.. ***
