发表机构
Nanoacademic Technologies Inc.; College of Physics and Optoelectronic Engineering, Shenzhen University; Department of Physics, McGill University（纳米学术技术有限公司; 深圳大学物理与光电工程学院; 麦吉尔大学物理系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过第一性原理计算比较晶态与非晶Al₂O₃势垒的约瑟夫森能量，发现非晶势垒因化学计量不均匀性导致E_J大幅波动，并揭示了逾渗隧穿路径的微观机制。
AI 中文摘要
约瑟夫森能量 $E_J$ 是决定transmon超导量子比特性质的关键参数。在Al/AlO$_x$/Al结中，$E_J$由电子隧穿超薄氧化物势垒决定，因此指数依赖于势垒的原子结构。我们基于NEGF-DFT量子输运方法，通过第一性原理器件建模计算$E_J$，将具有晶态Al$_2$O$_3$势垒的结与十个具有相同厚度的熔融淬火非晶Al$_2$O$_3$势垒的结进行比较。根据费米能级透射率和Ambegaokar–Baratoff关系，我们得到非晶系综的平均$E_J/h$为$2.78$ GHz，标准差为$4.67$ GHz，而晶态参考值为$0.73$ GHz；单个非晶值跨越近两个数量级。散射态分析表明输运是量子隧穿，变异性源于非晶氧化物的化学计量不均匀性：富铝低势垒区域可连接成类似逾渗的隧穿路径，强烈增强电导。一个实际的$200\ imes200$ nm$^2$结在超过$2\ imes10^4$个这样的微观区域上自平均。这些结果建立了从氧化物微观结构到超导电路能量尺度$E_J$的定量原子级路径。
英文摘要
The Josephson energy $E_J$ is a key parameter governing the properties of transmon superconducting qubits. In Al/AlO$_x$/Al junctions, $E_J$ is set by electron tunneling through an ultrathin oxide barrier and therefore depends exponentially on the atomic structure of the barrier. We compute $E_J$ by first-principles device modeling based on the NEGF-DFT quantum-transport method, comparing a junction with a crystalline Al$_2$O$_3$ barrier against ten junctions with melt--quenched amorphous Al$_2$O$_3$ barriers of the same thickness. From the Fermi-level transmission and the Ambegaokar--Baratoff relation, we obtain a mean $E_J/h$ of $2.78$ GHz for the amorphous ensemble, with a standard deviation of $4.67$ GHz, compared with $0.73$ GHz for the crystalline reference; individual amorphous values span nearly two orders of magnitude. Scattering-state analysis shows that transport is quantum tunneling and that the variability originates from stoichiometric inhomogeneity of the amorphous oxide: Al-rich, low-barrier regions can connect into percolation-like tunneling pathways that strongly enhance the conductance. A realistic $200\times200$ nm$^2$ junction self-averages over more than $2\times10^4$ such microscopic regions. These results establish a quantitative atomistic route from oxide microstructure to the superconducting-circuit energy scale $E_J$.
Comments5 figures
