Effects of Nonmagnetic Impurities and Subgap States on the Kinetic Inductance, Complex Conductivity, Quality Factor, and Depairing Current Density
Effects of Nonmagnetic Impurities and Subgap States on the Kinetic Inductance, Complex Conductivity, Quality Factor, and Depairing Current Density
复制标题
DOI：
10.1103/physrevapplied.17.014018
复制
发表时间：
2021-10
影响因子：
4.6
通讯作者：
Takayuki Kubo
中科院分区：
文献类型：
--
作者：
Takayuki Kubo
我们研究了非磁性杂质散射率γ和由Dynes Γ参数化的有限子隙态的组合如何影响与超导器件相关的各种物理量：动电感Lk，复电导率σ，表面电阻Rs，质量因子Q和相关电流密度Jd。所有的计算都是基于BCS理论的Eilenberger形式主义。我们假设器件材料是极端ii型s波超导体。众所周知，最佳杂质浓度（γ/∆0 ~ 1）使Rs最小。这里，∆0是温度T→0时理想（Γ→0）超导体的对电势。我们发现，对于清洁超导体（Γ /∆0 1），最佳Γ也可以将Rs降低一个数量级。此外，我们发现一种近乎理想的（Γ/∆0≪1）清洁极限超导体在很宽的频率ω范围内表现出与频率无关的r，这可以显著提高频率为几十GHz的非常紧凑腔体的Q。随着Γ或Γ的增加，平台消失，Rs服从ω 2依赖关系。本文还研究了子间隙状态引起的残余表面电阻Rres，并用srf级高q三维谐振器检测。我们分别计算了（γ，Γ， T）的单调增减函数Lk（γ，Γ， T）和Jd（γ，Γ， T）。器件材料的测量（γ，Γ）可以通过材料加工为工程（γ，Γ）提供有用的信息，从而有可能改善Q，工程Lk和改善Jd。
We investigate how a combination of a nonmagnetic-impurity scattering rate γ and finite subgap states parametrized by Dynes Γ affects various physical quantities relevant to to superconducting devices: kinetic inductance Lk, complex conductivity σ, surface resistance Rs, quality factor Q, and depairing current density Jd. All the calculations are based on the Eilenberger formalism of the BCS theory. We assume the device materials are extreme type-II s-wave superconductors. It is well known that the optimum impurity concentration (γ/∆0 ∼ 1) minimizes Rs. Here, ∆0 is the pair potential for the idealized (Γ → 0) superconductor for the temperature T → 0. We find the optimum Γ can also reduce Rs by one order of magnitude for a clean superconductor (γ/∆0 1). Also, we find a nearly-ideal (Γ/∆0 ≪ 1) clean-limit superconductor exhibits a frequency-independent Rs for a broad range of frequency ω, which can significantly improve Q of a very compact cavity with a few tens of GHz frequency. As Γ or γ increases, the plateau disappears, and Rs obeys the ω 2 dependence. The subgap-state-induced residual surface resistance Rres is also studied, which can be detected by an SRF-grade high-Q 3D resonator. We calculate Lk(γ,Γ, T ) and Jd(γ,Γ, T ), which are monotonic increasing and decreasing functions of (γ,Γ, T ), respectively. Measurements of (γ,Γ) of device materials can give helpful information on engineering (γ,Γ) via materials processing, by which it would be possible to improve Q, engineer Lk, and ameliorate Jd.