Investigation of the gap edge density of states at oxidized Niobium surfaces by RF measurements
Investigation of the gap edge density of states at oxidized Niobium surfaces by RF measurements
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通过射频测量研究氧化铌表面的能隙边缘态密度
DOI：
10.1109/tmag.1983.1062359
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发表时间：
1983
影响因子：
2.1
通讯作者：
J. Halbritter
中科院分区：
文献类型：
--
作者：
A. Philipp;J. Halbritter
超导Nb腔的调查产生温度和频率依赖性的表面电阻，这偏离BCS理论的预测均匀Nb和强烈依赖于Nb表面的氧化。增加氧化导致频率依赖性R\propto f^{\alpha}的斜率从α=1.55增加到α=1.86，并且导致折合能隙Δ（O）/kTc从1.92减小到1.76。频率依赖性可以用模糊的BCS态密度（DOS）来解释。拖尾的表观宽度随着氧化从2 e Δ（O）=0.05 meV增加到0.19 meV。能隙的减小可以部分地通过涂掉DOS来解释。此外，还必须考虑溶解氧对能隙的减小和氧簇的形成。不同氧化腔体的射频结果显示出能隙和DOS拖尾宽度之间的线性相关性。外推到零拖尾得到未畸变的能隙Δ（O）/kTc =1.975，这与多晶Nb隧穿研究的最佳结果Δ（O）= 1.56 meV非常一致。
Investigations of superconducting Nb cavities yield temperature and frequency dependences of the surface resistance, which deviate from the predictions of the BCS-theory for homogeneous Nb and strongly depend on the oxidation of the Nb surface. Increasing oxidation leads to an increase of the slope of the frequency dependence R\propto f^{\alpha} from α=1.55 to α=1.86 and to a decrease of the reduced energy gap Δ(O)/kT c from 1.92 to 1.76. The frequency dependence can be explained by a smeared out BCS density of states (DOS). The apparent width of the smearing increases with oxidation from 2eΔ(O)=0.05 meV to 0.19 meV. The energy gap reduction can partly be explained by smeared out DOS. In addition, the reduction of the energy gap by dissolved oxygen and the formation of oxygen clusters have to be taken into account. The rf results of differently oxidized cavities show a linear correlation between energy gap and width of the smearing of the DOS. Extrapolation to zero smearing yields an undistorted energy gap Δ(O)/kT c =1.975, which agrees well with the best result Δ(O) = 1.56 meV from tunneling investigations of polycristalline Nb.