Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka 142432, Russia.
Phys Rev Lett. 2018 Oct 26;121(17):177702. doi: 10.1103/PhysRevLett.121.177702.
We report the observation of a current-phase relation dominated by the second Josephson harmonic in superconductor-ferromagnet-superconductor junctions. The exotic current-phase relation is realized in the vicinity of a temperature-controlled 0-to-π junction transition, at which the first Josephson harmonic vanishes. Direct current-phase relation measurements, as well as Josephson interferometry, nonvanishing supercurrent and half-integer Shapiro steps at the 0-π transition self-consistently point to an intrinsic second harmonic term, making it possible to rule out common alternative origins of half-periodic behavior. While surprising for diffusive multimode junctions, the large second harmonic is in agreement with theory predictions for thin ferromagnetic interlayers.
我们报告了在超导-铁磁体-超导结中观察到的电流-相位关系，该关系主要由第二约瑟夫森谐波决定。这种奇特的电流-相位关系是在温度控制的 0 到 π 结转变附近实现的，在这个转变处，第一约瑟夫森谐波消失。直接的电流-相位关系测量以及约瑟夫逊干涉测量、在 0 到 π 转变处非零超导电流和半整数 Shapiro 台阶都一致指向一个固有第二谐波项，从而排除了半周期性行为的常见替代起源。虽然对于扩散多模结来说这是令人惊讶的，但大的第二谐波与对于薄铁磁层的理论预测相符。
