Degree Type


Date of Award


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Doctor of Philosophy


Physics and Astronomy


Josephson and quasiparticle tunneling measurements have been performed on superconducting LiTi(,2)O(,4). High quality, dense samples were made by arc melting LiTi(,2)O(,4) pellets produced by sintering con- stituent powders of Li(,2)CO(,3), Ti(,2)O(,3) and TiO(,2). The conductive spinel phase was recovered by annealing the ingot for about two months. The sample was characterized by X-ray diffraction and a.c. suscepti- bility, and it was shown to be in the correct crystal structure with only a slight amount of impurity and have a proper superconducting criti- cal temperature of 11.3 K. The measured density was about 99.3% of the single crystal value, hence the sample was dense and suitable for the tunneling experiment;Josephson point contact tunneling between LiTi(,2)O(,4) and Nb reveals, under K-band microwave radiation of frequency (nu) = 25.2 GHz, Shapiro steps of spacing approximately h(nu)/2e. Assuming the validity of the analysis of Pals and van Haeringen, we were led to the conclusion that the pairing in superconducting LiTi(,2)O(,4) was of the s-wave type, as in Nb;The "squeezable junction" method of Moreland and Hansma has been applied to study the superconducting energy gap of an arc melted bulk LiTi(,2)O(,4) sample and also of co-sputtered MoRe films. The MoRe film was estimated to have an energy gap of 1.05 mV, corre- sponding to a Re concentration of 17%. The energy gap of LiTi(,2)O(,4) is determined to be 1.95 (+OR-) 0.03 mV corresponding to 2(DELTA)/k(,B)T(,c) = 4.00 (+OR-) 0.06, making this material a conventional, electron-phonon strong coupled superconductor. The new results for LiTi(,2)O(,4) rule out the recent suggestion of Alexandrov and Ranninger that this material;might exhibit a bipolaronic form superconductivity, for such a form would be gapless, contrary to our results; *DOE Report IS-T-1245. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.



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Kwok-Wai Ng



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