Chen Zuhuang, Chen Zhanghui, Liu Z Q, Holtz M E, Li C J, Wang X Renshaw, Lü W M, Motapothula M, Fan L S, Turcaud J A, Dedon L R, Frederick C, Xu R J, Gao R, N'Diaye A T, Arenholz E, Mundy J A, Venkatesan T, Muller D A, Wang L-W, Liu Jian, Martin L W
Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Phys Rev Lett. 2017 Oct 13;119(15):156801. doi: 10.1103/PhysRevLett.119.156801. Epub 2017 Oct 11.
Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched LaMnO_{3}/SrTiO_{3} (001) heterostructures. Using a combination of element-specific x-ray absorption spectroscopy and dichroism, and first-principles calculations, interfacial electron accumulation, and ferromagnetism have been observed within the polar, antiferromagnetic insulator LaMnO_{3}. Our results show that the critical thickness for the onset of electron accumulation is as thin as 2 unit cells (UC), significantly thinner than the observed critical thickness for ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely induced by electron overaccumulation. In turn, by controlling the doping of the LaMnO_{3}, we are able to neutralize the excessive electrons from the polar mismatch in ultrathin LaMnO_{3} films and thus enable ferromagnetism in films as thin as 3 UC, extending the limits of our ability to synthesize and tailor emergent phenomena at interfaces and demonstrating manipulation of the electronic and magnetic structures of materials at the shortest length scales.
为了开发下一代氧化物电子学和自旋电子学，人们对极性-非极性氧化物界面处的涌现现象进行了深入研究。在此，我们报告了在极性失配的LaMnO₃/SrTiO₃(001)异质结构中，电子重构的临界厚度与铁磁性出现之间的解缠。通过结合元素特异性X射线吸收光谱和二向色性以及第一性原理计算，在极性反铁磁绝缘体LaMnO₃中观察到了界面电子积累和铁磁性。我们的结果表明，电子积累开始的临界厚度薄至2个晶胞(UC)，明显薄于观察到的铁磁性临界厚度5 UC。5 UC以下铁磁性的缺失可能是由电子过度积累引起的。反过来，通过控制LaMnO₃的掺杂，我们能够中和超薄LaMnO₃薄膜中极性失配产生的过量电子，从而使3 UC厚的薄膜具有铁磁性，扩展了我们在界面处合成和调控涌现现象的能力极限，并展示了在最短长度尺度上对材料电子和磁结构的操控。
