2007 年 76 巻 9 号 p. 094707
Superconducting wire network subjected to a uniform and a checkerboard-patterned magnetic field is investigated. The checkerboard field is created by an array of ferromagnetic dots placed on top of the superconducting network. Measurements of the current–voltage (I–V) characteristics have revealed the canonical Kosterlitz–Thouless–Berezinskii (KTB) transition at zero magnetic field. The superconducting transition at α=1⁄2 (α being the frustration parameter) is studied in detail, and compared with the theoretical predictions on the fully frustrated XY model which has a double degeneracy in the ground state vortex configuration. The I–V characteristics for α=1⁄2 is consistent with the scenario of kink–antikink unbinding at antiphase domain boundaries first proposed by Korshunov [Phys. Rev. Lett. 88 (2002) 167007]. Introduction of the checkerboard field with amplitude β to the α=1⁄2 case lifts the double degeneracy. The effect of non-zero β on the nature of superconducting transition at α=1⁄2 is consistent with this picture. The KTB transition is restored at β=1⁄2.
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