Dresden 2006 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 1: Superconductivity: Tunnelling, Josephson Junctions, SQUIDs

TT 1.6: Vortrag

Montag, 27. März 2006, 10:45–11:00, HSZ 02

From 0 to π coupled Josephson junctions — •Martin Weides¹, Hermann Kohlstedt^1,2, Edward Goldobin³, Dieter Koelle³, and Reinhold Kleiner³ — ¹Institute for Solid State Research, Research Centre Juelich, Germany — ²Department of Material Science and Department of Physics, University of Berkeley, USA — ³Physikalisches Institut - Experimentalphysik II, Universität Tübingen

We report on the successful fabrication of low- T_C SINFS Josephson junctions with 0 to π coupling transition as a function of d_F. Diluted ferromagnetic Ni₆₀Cu₄₀ is used as F-interlayer. Our technology [1] enables us to fabricate high quality junctions with low parameter spread. We studied [2] the dependence of I_c and β_C on the thickness of ferromagnet and on temperature for both coupling regimes. The influence of magnetic dead layer is investigated.
High I_c ≃ 5 A/cm² and V_c≃ 20 mV for the π coupled state [2] are measured. For T below 3 K the π coupled SINFS junction gets underdamped, indicating a rather weak Cooper pair breaking in the ferromagnetic layer.
At the 0-π boundary half-integer vortices (semifluxons) may spontaneously appear. They are pinned at the 0-π-boundary and may have two different polarities with flux Φ = ±Φ₀/2. The semifluxon represents the ground state of the system and therefore is extremely stable [3].
A patterning process of 0-π coupled SIFS junctions for the investigation of semifluxons was worked out and first results will be shown.

[1] Weides et al., to appear in Physica C

[2] Weides et al., to be submitted.

[3] E. Goldobin et al., PRB 66 (2002), 67 (2003), 69 (2004)