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    Homogeneous and inhomogeneous magnetic oxide semiconductors
    Xiao-Li Li(李小丽), Xiao-Hong Xu(许小红)
    Chin. Phys. B, 2019, 28 (9): 098506.   DOI: 10.1088/1674-1056/ab38ac
    Abstract457)   HTML    PDF (3231KB)(335)      

    Magnetic oxide semiconductors are significant spintronics materials. In this article, we review recent advances for homogeneous and inhomogeneous magnetic oxide semiconductors. In the homogeneous magnetic oxide semiconductors, we focus on the various doping techniques including choosing different transition metals, codoping, non-magnetic doping, and even un-doping to realize homogeneous substitution and the clear magnetic origin. And the enhancement of the ferromagnetism is achieved by nanodot arrays engineering, which is accompanied by the tunable optical properties. In the inhomogeneous magnetic oxide semiconductors, we review some heterostructures and their magnetic and transport properties, especially magnetoresistance, which are dramatically modulated by electric field in the constructed devices. And the related mechanisms are discussed in details. Finally, we provide an overview and possible potential applications of magnetic oxide semiconductors.

    Unconventional phase transition of phase-change-memory materials for optical data storage
    Nian-Ke Chen(陈念科), Xian-Bin Li(李贤斌)
    Chin. Phys. B, 2019, 28 (10): 104202.   DOI: 10.1088/1674-1056/ab3cc3
    Abstract446)   HTML    PDF (6399KB)(234)      
    Recent years, optically controlled phase-change memory draws intensive attention owing to some advanced applications including integrated all-optical nonvolatile memory, in-memory computing, and neuromorphic computing. The light-induced phase transition is the key for this technology. Traditional understanding on the role of light is the heating effect. Generally, the RESET operation of phase-change memory is believed to be a melt-quenching-amorphization process. However, some recent experimental and theoretical investigations have revealed that ultrafast laser can manipulate the structures of phase-change materials by non-thermal effects and induces unconventional phase transitions including solid-to-solid amorphization and order-to-order phase transitions. Compared with the conventional thermal amorphization, these transitions have potential superiors such as faster speed, better endurance, and low power consumption. This article summarizes some recent progress of experimental observations and theoretical analyses on these unconventional phase transitions. The discussions mainly focus on the physical mechanism at atomic scale to provide guidance to control the phase transitions for optical storage. Outlook on some possible applications of the non-thermal phase transition is also presented to develop new types of devices.
    Emerging properties of two-dimensional twisted bilayer materials
    Yang Cheng(程阳), Chen Huang(黄琛), Hao Hong(洪浩), Zixun Zhao(赵子荀), Kaihui Liu(刘开辉)
    Chin. Phys. B, 2019, 28 (10): 107304.   DOI: 10.1088/1674-1056/ab3e46
    Abstract339)   HTML    PDF (4901KB)(735)      
    Recent studies in van der Waals coupled two-dimensional (2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two layers, one can modulate their electronic band structures and therefore the associated electrical transport and optical properties, which are distinct from the original ones of each individual layer. These new properties excite great passion in the exploration of new quantum states and possible applications of 2D bilayers. In this article, we will mainly review the prevailing fabrication methods and emerging physical properties of twisted bilayer materials and lastly give out a perspective of this topic.
    Electrical transport and optical properties of Cd3As2 thin films
    Yun-Kun Yang(杨运坤), Fa-Xian Xiu(修发贤), Feng-Qiu Wang(王枫秋), Jun Wang(王军), Yi Shi(施毅)
    Chin. Phys. B, 2019, 28 (10): 107502.   DOI: 10.1088/1674-1056/ab3a91
    Abstract334)   HTML    PDF (4361KB)(266)      
    Cd3As2, as a three-dimensional (3D) topological Dirac semimetal, has attracted wide attention due to its unique physical properties originating from the 3D massless Dirac fermions. While many efforts have been devoted to the exploration of novel physical phenomena such as chiral anomaly and phase transitions by using bulk crystals, the development of high-quality and large-scale thin films becomes necessary for practical electronic and optical applications. Here, we report our recent progress in developing single-crystalline thin films with improved quality and their optical devices including Cd3As2-based heterojunctions and ultrafast optical switches. We find that a post-annealing process can significantly enhance the crystallinity of Cd3As2 in both intrinsic and Zn-doped thin films. With excellent characteristics of high mobility and linear band dispersion, Cd3As2 exhibits a good optical response in the visible-to-mid-infrared range due to an advantageous optical absorption, which is reminiscent of 3D graphene. It also behaves as an excellent saturable absorber in the mid-infrared regime. Through the delicate doping process in this material system, it may further open up the long-sought parameter space crucial for the development of compact and high-performance mid-infrared ultrafast sources.