Transport theory of ferromagnetic-insulator Josephson Junctions

DIPC Seminars

Speaker

Shiro Kawabata, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

When

2012/03/06
13:00

Place

Donostia International Physics Center (DIPC).Paseo Manuel de Lardizabal, 4 (nearby the Facultad de Quimica), Donostia

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"Transport theory of ferromagnetic-insulator Josephson Junctions" Shiro Kawabata National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan and LPMMC, Universite Joseph Fourier and CNRS, Grenoble, France A superconducting ring with a pi-junction made from superconductor (S) / ferromagnetic- metal (FM) / superconductor (S) exhibits a spontaneous current without an external magnetic field and the corresponding magnetic flux is half a flux quantum in the ground state [1]. Such a pi-ring provides so-called ”quiet qubit” that can be efficiently decoupled from the fluctuation of the external field [2]. However, the usage of FM gives rise to strong Ohmic dissipation. Therefore, the realization of pi-junctions without FM is highly desired for qubit applications. We have theoretically investigated the possibility of the pi-junction formation in the mesoscopic Josephson junctions with ferromagnetic insulators (FI) by taking into account the band structure of such materials explicitly [3]. In the case of the fully polarized FIs, e.g., La2BaCuO5 (LBCO) and K2CuF4, we found that novel atomic-scale 0-pi transition is induced by increasing the FI thickness [4]. In this talk, we will also discuss a robustness of the atomic-scale 0-pi transition as well as a possibility of of pi-coupling in a spin-filter Josephson junction [5]. References [1] L. N. Bulaevskii, V. V. Kuzii, and A. A. Sobyanin, JETP Lett. 25 (1977) 291. [2] L. B. Ioffe, V. B. Geshkenbein, M. V. Feigel'man, A. L. Fauchere, and G. Blatter, Nature 398 (1999) 679. [3] S. Kawabata, and Y. Asano, Low. Temp. Phys. 36 (2010) 1143. [4] S. Kawabata, Y. Asano, Y. Tanaka, A. A. Golubov, and S. Kashiwaya, Phys. Rev. Lett. 104 (2010) 117002. [5] K. Senapati, M. Blamire, and Z. Barber, Nature Mat. 10 (2011) 849.