Nguyen Tai, Hoang Van Hien, Koo Tae-Yeong, Lee Nam-Suk, Kim Heon-Jung
Department of Physics, College of Natural and Life Science, Daegu University, Gyeongbuk, 38453, Republic of Korea.
Pohang Acceleration Laboratory (PAL) and X-ray Free Electron Laboratory (XFEL), Pohang University of Science and Technology (POSTECH), Pohang, 37673, Republic of Korea.
Sci Rep. 2019 Dec 27;9(1):20145. doi: 10.1038/s41598-019-56744-w.
Over the last few decades, manipulating the metal-insulator (MI) transition in perovskite oxides (ABO) via an external control parameter has been attempted for practical purposes, but with limited success. The substitution of A-site cations is the most widely used technique to tune the MI transition. However, this method introduces unintended disorder, blurring the intrinsic properties. The present study reports the modulation of MI transitions in [10 nm-NdNiO/t-LaNiO/10 nm-NdNiO/SrTiO (100)] trilayers (t = 5, 7, 10, and 20 nm) via the control of the LaNiO thickness. Upon an increase in the thickness of the LaNiO layer, the MI transition temperature undergoes a systematic decrease, demonstrating that bond disproportionation, the MI, and antiferromagnetic transitions are modulated by the LaNiO thickness. Because the bandwidth and the MI transition are determined by the Ni-O-Ni bond angle, this unexpected behavior suggests the transfer of the bond angle from the lower layer into the upper. The bond-angle transfer eventually induces a structural change of the orthorhombic structure of the middle LaNiO layer to match the structure of the bottom and the top NdNiO, as evidenced by transmission electron microscopy. This engineering layer sequence opens a novel pathway to the manipulation of the key properties of oxide nickelates, such as the bond disproportionation, the MI transition, and unconventional antiferromagnetism with no impact of disorder.
在过去几十年里，为了实际应用目的，人们尝试通过外部控制参数来操控钙钛矿氧化物（ABO）中的金属 - 绝缘体（MI）转变，但成效有限。A位阳离子的取代是调节MI转变最广泛使用的技术。然而，这种方法会引入意外的无序，模糊了其固有特性。本研究报告了通过控制[10纳米 - NdNiO/t - LaNiO/10纳米 - NdNiO/SrTiO(100)]三层膜（t = 5、7、10和20纳米）中LaNiO的厚度来调制MI转变。随着LaNiO层厚度的增加，MI转变温度系统性降低，这表明键的歧化、MI转变和反铁磁转变受LaNiO厚度调制。由于带宽和MI转变由Ni - O - Ni键角决定，这种意外行为表明键角从下层转移到了上层。键角转移最终导致中间LaNiO层的正交结构发生结构变化，以匹配底部和顶部NdNiO的结构，这由透射电子显微镜证实。这种工程层序列为操控氧化物镍酸盐的关键特性，如键的歧化、MI转变和非常规反铁磁性，开辟了一条新途径，且不受无序的影响。
