Two-dimensional macroscopic quantum tunneling in multi-gap superconductor Josephson junctions

27th International Conference on Low Temperature Physics

Asai, Hidehiro^1 ; Kawabata, Shiro^1 ; Ota, Yukihiro^2 ; Machida, Masahiko^2

Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology(AIST), Ibaraki, Tsukuba

305-8568, Japan^1

CCSE, Japan Atomic Energy Agency, Chiba, Kashiwa

277-8587, Japan^2

关键词: Josephson coupling energies;    Macroscopic quantum tunneling;    Numerical calculation;    Potential energy landscapes;    Semi-classical approximation;    Superconducting phase;    Two-band superconductors;    Two-gap superconductor;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/568/2/022006/pdf
DOI  :  10.1088/1742-6596/568/2/022006

来源: IOP

【 摘 要 】

Low-temperature characters of superconducting devices yield definite probes for different superconducting phenomena. We study The macroscopic quantum tunneling (MQT) in a Josephson junction, composed of a single-gap superconductor and a two-gap superconductor. Since this junction has two kinds to The superconducting phase differences, calculating The MQT escape rate requires The analysis of quantum tunneling in a multi-dimensional configuration space. Our approach is The semi-classical approximation along a 1D curve in a 2D potential- energy landscape, connecting two adjacent potential (local) minimums through a saddle point. We find that this system has two plausible tunneling paths; an in-phase path and an out-of-phase path. The former is characterized by The Josephson-plasma frequency, whereas The latter is by The frequency of The characteristic collective mode in a two-band superconductor, Josephson- Leggett mode. Depending on external bias current and inter-band Josephson-coupling energy, one of them mainly contributes to The MQT. Our numerical calculations show that The difference between The in-phase path and The out-of-phase path is manifest, with respect to The bias- current-dependence of The MQT escape rate. This result suggests that our MQT setting be an indicator of The Josephson-Leggett mode.