Nickelate heterostructures as a laboratory for many-body physics

在两种不同材料之间具有精确控制界面的多层膜可以产生新的物理现象和功能，这些现象和功能不是由任何一种成分单独表现出来的，例如半导体多层膜中的量子霍尔效应和简单金属多层膜中的“巨磁阻”。过渡金属氧化物之间的界面可以表现出在半导体或普通金属界面上观察不到的特性，例如涌现的超导性和铁磁性，为新一代电子器件开辟了道路。在该项目中，将使用脉冲激光沉积以原子精度合成基于具有钙钛矿结构的镍酸盐的多层膜和超晶格，并使用共振X射线线性/圆二色性和反射仪，光谱椭圆偏振仪，像差校正高分辨率透射电子显微镜（ACHRTEM）和电子能量损失光谱（EELS）进行研究。本研究的目标是详细了解原子结构和界面处的电子性质之间的关系，特别关注价态，轨道占据和电荷传输。然后，通过改变组成层的厚度和化学成分、衬底施加的应变以及缺陷的浓度，以受控的方式操纵界面处的电子相互作用。最终，我们努力实现新的量子相，包括在先前的理论工作中预测的高温超导相。

Multilayers with precisely controlled interfaces between two different materials can give rise to novel physical phenomena and functionalities not exhibited by either of the constituents alone, like the quantum Hall effect in semiconductor multilayers and the “giant magnetoresistance” in multilayers of simple metals. Interfaces between transition-metal oxides can exhibit properties not observed at semiconductor or ordinary metal interfaces, such as emergent superconductivity and ferromagnetism, opening a path towards a new generation of electronic devices. In this project, multilayers and superlattices based on nickelates with perovskite structure will be synthesized with atomic precision using pulsed-laser deposition, and investigated with resonant X-ray linear/circular dichroism and reflectometry, spectral ellipsometry, aberration-corrected high-resolution transmission electron microscopy (ACHRTEM) and electron energy loss spectroscopy (EELS). The goal of this investigation is a detailed understanding of the relationship between the atomic structure and the electronic properties at the interfaces, with particular focus on the valence states, orbital occupation, and charge transport. The electronic interactions at the interface will then be manipulated in a controlled fashion by varying the thickness and chemical composition of the constituent layers, the strain imposed by the substrate, and the concentration of defects. Ultimately, we strive to realize new quantum phases, including a high-temperature superconducting phase predicted in prior theoretical work.