复杂氧化物中电子相分离的量子调控

Quantum manipulation of electronic phase separation in complex oxides

复杂氧化物可以呈现出高温超导、庞磁阻以及多铁效应等诸多新奇的物理现象.这类材料中的电荷/自旋/轨道和晶格自由度之间的强耦合相互作用,可以导致多种相互竞争且能量非常接近的电子态的空间共存,这就是电子相分离现象.如果可以将材料的空间尺寸缩小到电子相分离的特征长度,其物理性质甚至电子关联作用本身都会发生根本的变化,从而有可能实现复杂氧化物中的量子调控.本文综述了我们课题组在过去几年中针对复杂氧化物中电子相分离的量子调控取得的进展,内容包括:发现了锰氧化物边缘电子态,通过氧化物微纳加工技术,实现了量子态空间分布的调控,提高了庞磁阻锰氧化物的临界温度;研究了当材料空间尺度小于其电子相分离特征尺度时电子相分离的表现,确定了在电子相分离消失以后体系的磁结构;通过超晶格生长技术调控了材料中的掺杂有序度,对锰氧化物中大尺度的电子相分离的物理机理从实验上给出了解释.

Complex oxides system displays exotic properties such as high temperature superconductivity, colossal magnetoresistance and multiferroics. Owing to the strong correlation between lattice, spin, charge and orbital degrees of freedom,competing electronic states in complex oxides system often have close energy scales leading to rich phase diagrams and spatial coexistence of different electronic phases known as electronic phase separation（EPS）. When the dimension of complex oxides system is reduced to the length scale of the correlation length of the EPS, one would expect fundamental changes of the correlated behavior. This offers a way to control the physical properties in the EPS system. In this paper, we review our recent works on electronic phase separation in complex oxide systems. We discovered a pronounced ferromagnetic edge state in manganite strips; by using lithographic techniques, we also fabricated antidot arrays in manganite, which show strongly enhanced metal-insulator transition temperature and reduced resistance. Moreover, we discovered a spatial confinement-induced transition from an EPS state featuring coexistence of ferromagnetic metallic and charge order insulating phases to a single ferromagnetic metallic state in manganite. In addition, by using unit cell by unit cell superlattice growth technique, we determined the role of chemical ordering of the dopant in manganite. We show that spatial distribution of the chemical dopants has strong influence on their EPS and physical properties. These works open a new way to manipulate EPS and thus the global physical properties of the complex oxides systems, which is potentially useful for oxides electronic and spintronic device applications.