Evidence for Crossed Andreev Reflection in (100)YBa2Cu3O7-δ-SrRuO3 superconductor-ferromagnet bilayers
Evidence for Crossed Andreev Reflection in (100)YBa2Cu3O7-δ-SrRuO3 superconductor-ferromagnet bilayers
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(100)YBa2Cu3O7-δ-SrRuO3 超导-铁磁体双层中交叉安德烈夫反射的证据
DOI：
10.1117/12.621040
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发表时间：
2005
影响因子：
8.6
通讯作者：
G. Koren
中科院分区：
文献类型：
--
作者：
O. Millo;I. Asulin;O. Yuli;G. Koren
由于超导体-铁磁体结的铁磁侧是自旋极化的，因此Andreev反射被抑制。因此，铁磁体中的感应超导体序参数预计会迅速衰减，大约为几nm。我们对（100）YBa_2Cu_3O_（7-δ）-SrRuO_3（YBCO-SRO）双层外延薄膜的扫描隧道谱测量表明，在SRO中，超导体序参量在大部分结区消失的距离小于8 nm。然而，我们发现局部区域，沿着窄（<10 nm）的条纹，在那里的序参数（超导体的间隙结构）穿透铁磁体超过20 nm。这归因于发生在畴边界处的“交叉Andreev反射”，其中来自一个磁畴的电子被逆反射为在相邻畴中具有相反自旋的空穴。这种现象，直接观察到这里的第一次，可以解释（不丰富）的情况下，发现在超导铁磁邻近系统的长程邻近效应。
Since the ferromagnetic side of a superconductor-ferromagnet junction is spin polarized, Andreev reflections are suppressed. Consequently, the induced superconductor order parameter in the ferromagnet is expected to decay rapidly, on the order of a few nm. Our scanning tunneling spectroscopy measurements on thin epitaxial (100)YBa2Cu3O7-δ-SrRuO3 (YBCO-SRO) bilayers, where SRO is a ferromagnet, indeed show that on most of the junction area the superconductor order parameter vanishes in the SRO over a distance less than 8 nm. However, we find localized regions, arranged along narrow (<10 nm) stripes, where the order parameter (superconductor-like gap structure) penetrates the ferromagnet more than 20 nm. This is attributed to "crossed Andreev reflections", taking place at domain boundaries, where an electron from one magnetic domain is retro reflected as a hole with opposite spin in an adjacent domain. This phenomenon, directly observed here for the first time, may account for the (not abundant) cases where a long-range proximity effect was found in superconductor-ferromagnet proximity systems.