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NÃºÃ±ez Regueiro, M., P. Esquinazi, M. A. Izbizky, C. Duran, D. Castello, J. Luzuriaga, and G. Nieva. "Evidence of tunneling systems through thermal and acoustic measurements in ceramic materials." Physica C: Superconductivity and its applications 153-155, no. PART 2 (1988): 1016–1017.
Abstract: We have neasured the sound velocity, internal friction, thermal conductivity and specific heat of La-based and (Y/Eu)- based ceramics. The low temperature data can be understood in terms of the Tunneling Model assuming the existence of Tunneling Systems (TS). From these measured properties we obtain values for the parameter C=P?2/?v2, where P is the density of states of TS, ? the coupling constant between phonons and TS, ? the mass density and v the sound velocity close to those obtained for amorphous and “orientational” disordered crystalline materials. Our data would indicate that the TS are intrinsic defects independent of the sample porosity.