Deconfinement of vortices with continuously variable fractions of the unit flux quanta in two-gap superconductors

Date & Time
2 November 2006 (Thu), 3:00 pm - 4:30 pm
Place
8F large seminar room, Sengen site
Speaker
Dr. Jun Goryo(御領潤博士)
Affiliation
Department of Physics, Aoyama-Gakuin University(青山学院大学理工学部物理学科)
Title
Deconfinement of vortices with continuously variable fractions of the unit flux quanta in two-gap superconductors
2ギャップ超伝導体における分数磁束量子を持つ渦糸の理論研究
Abstract
We propose a new stage for observing a confinement-decofinement transition in the laboratory. In two-gap superconductors such as MgB2, there are two species of vortices, each carrying a continuously variable fraction of the unit flux quanta ψ0= hc/2e. The confined state of these two is the usual vortex which is stable in the low temperature region of the system under a certain magnetic field above Hc1. An entropy gain causes the two fractional vortices to be deconfined above a certain temperature. Here we see an analogy to quarks in a charged pion. We estimate the condition of the deconfinement by using parameters for a thin film of the typical two-gap superconductor MgB2.
MgB2に代表されるような2ギャップ超伝導体においては二つの超伝導成分に対応した二種類の渦糸が存在する。そして各々単位磁束量子ψ0= hc/2e の分数倍の磁束を持つ。Hc1以上の磁場のもとで、低温ではこの二種類の渦糸は束縛状態を作り、通常の単位磁束量子を持つ。しかし或る温度を超えるとエントロピックな効果により非閉じ込め転移を起こし、分数磁束量子を持つ渦糸が遊離するという結果を得た。MgB2の薄膜に関するパラメータに基づきこの転移温度を見積もる。
Contact
Dr. Akihiro Tanaka (田中秋広)