表面声子软化和量子尺寸效应对纳米结构Pb超导性质的竞争效应
Competing effects of surface phonon softening and quantum size effects on the superconducting properties of nanostructured Pb
摘要：
纳米结构Pb的超导转变温度（TC）随着颗粒尺寸从65 nm减小到7 nm而保持几乎恒定，低于该尺寸，超导性会突然丧失。与此相反，有一个大的增强在上临界场（HC 2）在相同的尺寸制度。通过测量Al/Al_2O_3/nano-Pb平面隧道结中超导能隙的温度依赖性，探讨了纳米结构Pb在如此大的颗粒尺寸范围内的TC异常鲁棒性的起源。我们发现，在22 nm以下，电子-声子耦合强度随着颗粒尺寸的减小而单调增加，并且几乎完全补偿了量子尺寸效应，这有望抑制TC。
英文摘要：
The superconducting transition temperature (TC) in nanostructured Pb remains nearly constant as the particle size is reduced from 65 to 7nm, below which size the superconductivity is lost rather abruptly. In contrast, there is a large enhancement in the upper critical field (HC2) in the same size regime. We explore the origin of the unusual robustness of the TC over such a large particle size range in nanostructured Pb, by measuring the temperature dependence of the superconducting energy gap in planar tunnel junctions of Al/Al2O3/nano-Pb. We show that below 22nm, the electron phonon coupling strength increases monotonically with decreasing particle size, and almost exactly compensates for the quantum size effect, which is expected to suppress TC.
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