| Summary: | 碩士 === 國立成功大學 === 物理學系碩博士班 === 95 === The superconductivity of gallium in a compact package of equal-size silica spheres with diameters 210 and 250 nm has been investigated by magnetic measurements. Since only half of the cavities between the touching spheres are filled with gallium, the gallium grains in cavities are well separated and apt to be considered as isolated particles. A direct measurement of superconducting transitions indicated that these gallium nanoparticles are composed of ��-Ga with small amount of ��-Ga or ��-Ga. The Tc of ��-Ga, ��-Ga, and ��-Ga in these nanoparticles are still 6.1, 7.0, and 7.8 K respectively, which is exactly the same as those in a bulk gallium. The upper critical fields of these gallium grains in opals can be described as Hc2 = H0 [1- (T/Tc)�娭 with �� ~ 2.9. The H0 are 3.4 and 3.6 kOe for gallium in 210 and 250 nm samples respectively, which is nearly six times as large as the critical field (560 Oe) of bulk ��-Ga. The zero-field-cooled magnetization MZFC(T) and the real components of ac susceptibilities �荂�(T) drop significantly at ~2 K, which might relate to a new superconducting phase with critical temperature at ~ 2 K.
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