Novel nonequilibrium phenomena and phase transitions in superconducting vortex systems

2020 Fiscal Year Final Research Report

• Project/Area Number: 17H02919
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Okuma Satoshi 東京工業大学, 理学院, 教授 (50194105)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 渦糸 / 非平衡相転移 / 動的秩序化 / ディピニング転移 / 可逆不可逆転移 / 相分離 / 走査トンネル分光 / アモルファス超伝導膜

Outline of Final Research Achievements

Quantized magnetic fluxes (vortices) in superconductors are regarded as a two-dimensional particle system on a random substrate. When a dc or ac driving force applied to vortices is increased, a final state undergoes a transition from a quiescent to flowing state. This is called a depinning transition. In case of ac drive, in the transient state the vortices self-organize to avoid next collisions. With an increase in the ac shear amplitude, a final state undergoes a transition from a reversible state where all particles return to their initial position to an irreversible state where some particles do not return. This is called a reversible-irreversible transition. In this work, we have demonstrated that these two transitions caused by ac drive fall into the same universality class as the absorbing transition in DP. We have also found a novel phenomenon that the final vortex configuration formed with the ac force superimposed with the dc one comprises organized and disordered regions.

Free Research Field

低温物理, 超伝導, 非平衡物理

Academic Significance and Societal Importance of the Research Achievements

本研究は, 運動の中から秩序は如何に作られるか？という基本的な問の学理に迫るものであり, 大きな普遍性をもつ。ディピニング転移は応用上も重要な固体間の摩擦や強磁性体の磁壁の運動に, 可逆不可逆転移は固体の降伏現象・塑性変形や生物の集団運動などに現れ, これらを包含する吸収状態転移は, 浸透や触媒反応, 流体の目詰り現象, あるいは感染や山火事のモデルとなるなど社会への波及性は大きい。