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arXiv 1707.03029cond-mat.str-elcond-mat.supr-con
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(111)LaAlO $_3$ / SrTiO $_3$界面超导态的磁电阻

Magnetoresistance in the superconducting state at the (111) LaAlO$_3$/SrTiO$_3$ interface

S. Davis, Z. Huang, K. Han, Ariando, T. Venkatesan, V. Chandrasekhar

摘要:

由于传统的自旋单重态超导和铁磁有序之间的对抗关系,同时表现出超导性和铁磁性的凝聚态系统是罕见的。在已知超导性和磁序共存的材料中(例如一些重费米子材料),超导性被认为是非常规的性质。最近,生活在钙钛矿带绝缘体LaAlO $_3$(LAO)和SrTiO $_3$(STO)之间的界面处的导电气体也被证明具有超导性和磁性。大多数以前的研究集中在LAO/STO样品,其中界面是在(001)晶面。相对较少的工作集中在(111)晶体取向上,它在界面处具有六方对称性,并被预测具有潜在的有趣拓扑性质,包括非常规超导配对状态。在这里,我们报告的(111)LAO/STO异质结的磁阻测量温度下,他们也超导。与(001)结构一样,磁电阻是滞后的,表明磁性和超导性共存,但另外,我们发现这种磁电阻是各向异性的。这种各向异性的响应在超导状态下是完全出乎意料的,并且表明(111)LAO/STO异质结构可能支持非常规的超导性。

英文摘要:

Condensed matter systems that simultaneously exhibit superconductivity and ferromagnetism are rare due the antagonistic relationship between conventional spin-singlet superconductivity and ferromagnetic order. In materials in which superconductivity and magnetic order is known to coexist (such as some heavy-fermion materials), the superconductivity is thought to be of an unconventional nature. Recently, the conducting gas that lives at the interface between the perovskite band insulators LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) has also been shown to host both superconductivity and magnetism. Most previous research has focused on LAO/STO samples in which the interface is in the (001) crystal plane. Relatively little work has focused on the (111) crystal orientation, which has hexagonal symmetry at the interface, and has been predicted to have potentially interesting topological properties, including unconventional superconducting pairing states. Here we report measurements of the magnetoresistance of (111) LAO/STO heterostructures at temperatures at which they are also superconducting. As with the (001) structures, the magnetoresistance is hysteretic, indicating the coexistence of magnetism and superconductivity, but in addition, we find that this magnetoresistance is anisotropic. Such an anisotropic response is completely unexpected in the superconducting state, and suggests that (111) LAO/STO heterostructures may support unconventional superconductivity.

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