| Summary: | 碩士 === 國立中正大學 === 物理學系 === 85 === AbstractThe agreement of the transition temperature Tc = 1.85 ~
2.15 K (10 ~ 90 % values) measured by dc-susceptibility and
heat-capacity techniques provides clear evidence of bulk
superconducting phase in LaNiGa2. The normal-state specific-heat
data can be fitted to the expression Cn = gT + bT3 (2.0 K < T <
5.9 K) by a least-squares analysis, where c ~ 11.64 mJ/mol K2
and b ~ 0.332 mJ/mol K4, resulting in a Debye temperature qD ~
560 K. Below Tc (1 K < T < 2 K) , the specific-heat data has a
dominant low-temperature behavior of the form exp[-D(0) / kBT],
where the ratio 2D(0)/ kBTc ~2.64 (Tc = 2 K) which is smaller
than 3.5 as predicted by the weak-coupling BCS model. We have
also estimated the value DC/ gTc from the measured specific-heat
jump DC (25 mJ/mol K) at Tc, DC/ gTc ~ 1.074 which is smaller
than 1.43 as predicted by BCS model. From the comparison of the
observed values of 2D(0)/ kBTc and DC/ gTc with those predicted
by BCS model, respectively along with the examination of the
pattern of X-ray diffraction where certain impurity phase
appeared , we may estimate that there exist about 25 % of
impurity in the sample, which is confirmed to show no
superconductivity in low temperature. In addition, LaNiGa2 is
the first nickel-based ternary-galliumide superconductor.
|
|---|
