不可能と思われていた「一方向性超伝導体」を発見(Discovery of the one-way superconductor, thought to be impossible)

2022-04-28 オランダ・デルフト工科大学（TUDelft)

＜関連情報＞

• https://www.tudelft.nl/en/2022/tnw/discovery-of-the-one-way-superconductor-thought-to-be-impossible
• https://www.nature.com/articles/s41586-022-04504-8

ファンデルワールスヘテロ構造における無電界ジョセフソンダイオード The field-free Josephson diode in a van der Waals heterostructure

Heng Wu,Yaojia Wang,Yuanfeng Xu,Pranava K. Sivakumar,Chris Pasco,Ulderico Filippozzi,Stuart S. P. Parkin,Yu-Jia Zeng,Tyrel McQueen &Mazhar N. Ali
Nature  Published: 27 April 2022
DOI:https://doi.org/10.1038/s41586-022-04504-8

Abstract

The superconducting analogue to the semiconducting diode, the Josephson diode, has long been sought with multiple avenues to realization being proposed by theorists^1,2,3. Showing magnetic-field-free, single-directional superconductivity with Josephson coupling, it would serve as the building block for next-generation superconducting circuit technology. Here we realized the Josephson diode by fabricating an inversion symmetry breaking van der Waals heterostructure of NbSe₂/Nb₃Br₈/NbSe₂. We demonstrate that even without a magnetic field, the junction can be superconducting with a positive current while being resistive with a negative current. The ΔI_c behaviour (the difference between positive and negative critical currents) with magnetic field is symmetric and Josephson coupling is proved through the Fraunhofer pattern. Also, stable half-wave rectification of a square-wave excitation was achieved with a very low switching current density, high rectification ratio and high robustness. This non-reciprocal behaviour strongly violates the known Josephson relations and opens the door to discover new mechanisms and physical phenomena through integration of quantum materials with Josephson junctions, and provides new avenues for superconducting quantum devices.