钙钛矿锰氧化物/铁电体外延复合结构在可控应力畸变下的多场量子调控效应

In this proposed research we will achieve tunable electromagnetic properties in novel manganite/ferroelectric heterostructures by multi-fields under controlled lattice deformation, which is induced by the electrostrictive/piezoelectric effect in the integrated ferroelectric layer/substrate. Our preliminary results showed that significant modulation on resistivity and magnification can be well tuned by the strain field induced by lattice deformation. We will further investigate the effects by multi-fields (electric, optic, magnetic), together with the well-controlled lattice strain, on electromagnetic properties and quantum states in such heterostructures combined with manganite and ferroelectrics. Piezoelectric behavior of the employed ferroelectrics and its influence on the lattice distortion induced in manganites will be systematically studied. As the manganites are integrated with ferroelectrics, such composite heterojunctions may exhibit enhanced tunability and exceptional mechanical, magnetic and electronic properties that have not been observed in their bulk counterparts alone. The feasibility to utilize such strain-mediated ?eld-effects for sensors/devices applications will be explored. It may reveal some other fascinating features in such a complex, which includes controlled switching of rich functionality such as ferromagnetism, electroresistance, and magnetoresistance, and may lead to development of novel functional field-effect transistors.

本项目拟在压电晶体上外延生长钙钛矿型过渡金属锰氧化物获得低维的人工复合体系，并通过铁电晶体的场致伸缩效应引入可控的晶格畸变，从微观和宏观尺度上系统研究应力场下的电磁耦合及量子调控效应，探测其丰富的量子现象。我们拟通过电光磁的多场调控，研究锰氧化物低维体系在可控晶格应力场中亚稳特性的变化规律，以其获得增强的调控效应。对比研究静电场、交变电场、偏置电流、光辐照及外磁场对共存相畴和电荷有序畴的作用（分布、导电性、移动和融化），揭示其亚稳态中出现的物理过程。从微观角度理解非欧姆特性（如场致电阻、磁电阻）与电荷有序畴之间的关系，阐述相分离体系中场致电阻和磁电阻效应的关联及其内在机理。本项研究不仅对深入理解钙钛矿型锰氧化合物中亚稳特性和量子调控的物理机制具有重要意义，而且对探索电流/电场敏感的新型电子功能器件具有实际意义。

在本课题的研究中，我们运用铁电体的伸缩效应实时控制应力和晶格畸变，同时引入电光磁的多场调控，系统地研究了功能氧化物/铁电体低维复合体系在可控晶格应力场作用下亚稳特性的量子调控及其变化规律。.为了实现异质材料的完美复合和可控生长，我们采用先进的激光分子束外延技术制样，基本上掌握了各种锰氧化物与铁电体的合成条件，实现了原子尺度上晶格结构与异质界面的精准控制和合成。在课题实施中我们设计和制备了各种不同的过度族金属氧化物在铁电晶体上的外延生长。.我们选用晶格相容性优异的PMN-PT铁电体作为应力源，通过极化电场实时调控功能氧化物/铁电体外延低维结构的应力与晶格畸变，实现了原位可调控应力场并研究了应力下其磁性、电输运、铁电等物性的变化。由于晶格畸变改变了双交换耦合强度和Jahn-Teller 畸变，进而导致晶格的结合能及键角度的改变，由此我们可以调控氧化物材料的宏观物理性能（如居里点、金属-绝缘体相变、CMR、相分离等）。实验发现，氧化物低维复合体系表现出对外场调制的强烈响应和敏感性，如n-La1-xHfxMnO3/Nb:STO/p-Si异质结中大幅增强的光电阻、通过压电效应达在光敏晶体SrRuO3/PMNPT（111）外延体系上达到的光电共控、光场与电场之间的强关联、LHMO中的场致电阻效应、以及BaTiO3/LCMO和TiO2/PMN-PT铁电外延结构中由多场量子调控效应导致的开关行为等。我们全面探索了静电场、交变电场、偏置电流、光辐照及外磁场对共存相畴和电荷有序畴的作用，对其亚稳态中出现的物理过程有了更深入、更系统的理解和认识，并进一步阐明相分离体系中场致电阻和磁电阻效应、光电磁特性的关联及其内在机理。.我们还探索了这些氧化物异质复合体系在微电子器件方面的应用前景，如LHMO/PMN-PT复合体系的场致电阻与场效应、LaAlO3/STO结构中由光诱导的二维电子导电性、n-La1-xHfxMnO3/Nb:STO/p-Si外延结构的优秀整流特性及超强的光电阻、TiO2/PMN-PT铁电异质结的室温开关效应、BaTiO3/LaCaMnO结构中基于铁电极化诱导的记忆行为等。这些极具应用前景的研究结果无疑为发展新一代的微纳传感器件和记忆元件开拓了新的领域。.本课题的实施过程很顺利，基本达到了课题原定的目标和任务。