講演者： Sung G. Chung 氏（Physics & Nanotechnology Research and
Computation Center, Western Michigan University, USA）
日時： ２月　２８日（火）　　午後４時３０分から
場所： 青山学院大学　理工学部（相模原キャンパス）Ｌ棟６階　Ｌ６０３室

題目： 「Spontaneous symmetry breaking in Josephson junction arrays」

要旨：
The superconductor-insulator transition in the two dimensional XY
model is identified as a spontaneous symmetry breaking.  The strong
size dependence in the spontaneous symmetry breaking predicts an order
of magnitude increase in the critical coupling constant Ej/T with the
array size, where Ej is the Josephson energy and T the temperature.
The order of magnitude change experimentally observed in the critical
coupling constant Ej/Ec, where Ec is the Coulomb energy, from a single
Josephson junction to the 48x40 arrays with ultra-small island sizes
may be accounted for likewise with an opposite tendency in the quantum
phase transition in contrast to the classical phase transition in the
XY model; the critical Ej/Ec decreases with the array size.  Our
spontaneous-symmetry-breaking theory bridges the two limiting cases;
the Likharev-Zorin band theory for the single Josephson junction and
the Berezinskii-Kosterlitz-Thouless transition in the infinite-size
limit. 

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共催：　青山学院大学　理工学会