We have investigated the superconducting transition temperature T _c depression and magnetic-field-induced quantum critical behavior in three-dimensional (3D) polycrystalline niobium (Nb) films. For superconducting films with 26.8 nm 72.9 nm, the T _c value increases from ∼4.94 to ∼8.74 K. Through comparing our experimental data with proximity effect and weak localization effect, the T _c depression can be explained by the proximity effect predicted by Cooper. Pure size effect could not induce T _c depression because the average energy level spacing of grains is much smaller than the bulk Nb superconducting energy gap. The reason for the proximity effect is the metallic niobium monoxide NbO surrounding Nb grains. The superconductor-insulator transition (SIT) induced by magnetic field has been observed in T _s   433 and 523 K films. The critical field B _c in SIT satisfies a scaling relationship, similar to that caused by quantum phase transition in a two-dimensional (2D) cleaning system. The reason for that is the average polycrystalline grain size is smaller than the bulk Nb coherence length. The quantum effect is probably related to the Nb oxides.

我们研究了三维 (3D) 多晶铌 (Nb) 薄膜中的超导转变温度T _c降低和磁场诱导的量子临界行为。对于 26.8 nm 至72.9 nm 的超导薄膜，T _c值从~4.94 增加到~8.74 K。通过将我们的实验数据与邻近效应和弱定域效应进行比较，可以通过 Cooper 预测的邻近效应来解释T _c下降。纯尺寸效应不能诱导牛逼_Ç 因为晶粒的平均能级间距远小于体 Nb 超导能隙。邻近效应的原因是围绕 Nb 晶粒的金属一氧化铌 NbO。在T _s  433 和 523 K 薄膜中观察到由磁场引起的超导体-绝缘体转变（SIT）。SIT 中的临界场B _c满足缩放关系，类似于二维 (2D) 清洁系统中由量子相变引起的缩放关系。其原因是平均多晶晶粒尺寸小于块状 Nb 相干长度。量子效应可能与 Nb 氧化物有关。