过渡金属氧化物中新奇量子态与电荷-自旋互转换研究进展

Research progress of novel quantum states and charge-spin interconversion in transition metal oxides

为了满足信息技术时代下海量数据的高效存储及处理,具有低功耗、非易失性的自旋电子器件受到极大关注.能够高效产生自旋流的自旋源材料是新型自旋-轨道力矩器件的重要组成部分.近二十年来,在探索具有高效产生自旋流的材料体系,以及理解材料相关物理机制两方面都取得了较大的进展.最近,在过渡金属氧化物中涌现出许多与产生自旋流密切相关的新奇量子态,成为自旋源的新兴材料体系被广泛研究.研究结果表明,过渡金属氧化物具有对电子结构高度敏感、显著且灵活可调的电荷-自旋转换效率,具有巨大的应用潜力.本文主要综述了过渡金属氧化物中新奇的电子能带结构及其与电荷-自旋互转换的关联机制,并对未来的发展趋势进行了展望.

For efficient storage and processing of massive data in the information technology era,spintronic device attracts tremendous attention due to its low power consumption and non-volatile feature.Spin source material,which can efficiently generates spin current,is an important constituent of novel spin-orbit torque device.The efficiency of spin current generation in spin source material directly determines the performances of various spintronic devices.In the past two decades,great progress has been made in exploring high-efficient spin source material systems and understanding the relevant physical mechanisms.A wide variety of materials are explored,ranging from traditional heavy metals and semiconductors to topological insulators and two-dimensional(2D)materials.Recently,the material family of transition metal oxides attracts tremendous attention due to its efficient and highly tunable charge-spin conversion intimately related to its emerging novel quantum states and electronic structure.The mechanism of charge-spin conversion generally has two contributions:the bulk spin Hall effect and the spin-momentum locked interface with inversion symmetry breaking.Novel electronic structures such as topological band structures and spin-momentum locked surface states can realize efficient charge-spin conversion.For example,the Weyl points in SrRuO_(3) and the topological Dirac nodal line in SrIrO_(3) are predicted to give rise to a large Berry curvature and corresponding spin Hall conductance;the topological surface states can generate spin accumulation due to spin-momentum locking;the Rashba states at the oxide interface such as the 2D electron gas in SrTiO_(3) and KTaO_(3) can generate spin current by Rashba-Edelstein effect.Furthermore,the entanglement of various degrees of freedom,including spin,charge,lattice and orbit in transition metal oxides lead to the electronic structure being highly tunable by various methods including gate voltage,substrate constraint,thickness,interface engineering,etc.Therefore,charge-spin conversion in transition metal oxides is of great significance for both modulating of novel electronic structure in fundamental research and exploring its promising potential in future spintronic devices.In this review,we focus on introducing aspects of exotic electronic structures,spin transport mechanism,charge-spin interconversion characterization,efficiency and manipulation in transition metal oxides,and giving a prospect on the future development trend.