Establishment and application of a current-inducing method to observe superconducting Higgs modes

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K13496
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: The University of Tokyo
• Principal Investigator: Nakamura Sachiko 東京大学, 低温科学研究センター, 特任助教 (00726317)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 超伝導 / ヒッグスモード / 電流注入 / テラヘルツ / 光学伝導度

Outline of Final Research Achievements

This research established a new observation method of superconducting Higgs mode where the optical conductivity around the superconducting gap energy in the presence of dc supercurrents.
The Higgs mode is the collective excitation of the amplitude of the superconducting order parameter, which does not generally couple to electromagnetic waves in the linear conducting regime because it does not associate with electric nor magnetic polarizations. However, it was theoretically predicted that the Higgs mode can be observed as a linear absorption if a dc current is introduced to the superconductor. We measured the terahertz conductivity of superconducting thin films in the presence of large dc currents and demonstrated the prediction qualitatively and quantitatively.

Free Research Field

物性物理学実験

Academic Significance and Societal Importance of the Research Achievements

超伝導ヒッグスモードは、超伝導体における超伝導秩序の成長や抑制をピコ秒の超高速なタイムスケールで観測できるプローブである。
ヒッグスモードは電磁場との相互作用が非線形なので、通常は高強度の光源を用いて観測・駆動するが、本研究は、電流注入下なら線形の相互作用が実効的に現れるので、低強度の光源でも観測・駆動できることを示した。ヒッグスモードの対象を、高強度光源の実現が難しい周波数帯域にヒッグスモードが現れる物質系だけでなく、測定による擾乱が小さいことで、光誘起した過渡的または準安定な非平衡状態にも広げる重要な成果である。