封面文章

物理学

来源出版物：SCIENCE CHINA Physics，Mechanics & Astronomy，2015，58（3）： 034202联系邮箱：REN Yuxuanyxren@ustc.edu.cn

封面介绍：在半导体中注入自旋形成兼具电荷属性和自旋特性的稀磁半导体可以制成自旋阀、自旋二极管、高密度非易失性存储器以及磁感应器等新型的功能器件，具有诱人的应用前景.但是向传统的Ⅲ-Ⅴ族化合物半导体中掺杂存在两点不足.首先，传统的稀磁半导体在引入自旋的同时也引入了载流子，这种自旋和电荷的捆绑效应严重制约了电性和磁性的调控维度.其次，基于掺杂中的不等价代替导致磁性离子化学溶解度严重受限，平均溶解度不足 1%，仅可形成亚稳态薄膜材料.而Ⅰ-Ⅱ-Ⅴ族基新型稀磁半导体 Li（Mg，Cu）N，在Mg2+位引入Cu2+，可以使体系产生半金属铁磁性.载流子浓度则通过改变Li的含量来进行调控，这样就实现了稀磁半导体电性和磁性的分离调控.而且等价掺杂可以使得体系具有较高的Cu固溶度，从而使体系居里温度提高，很好地克服了传统稀磁半导体的不足.封面显示的是通过改变Li的含量调控Cu掺杂LiMgN体系性能的晶体结构.详见邓军权等人文（p830）.

新型稀磁半导体Cu掺杂LiMgN的电子结构和光学性质

邓军权，毋志民，杨武庆，等

采用基于密度泛函理论的第一性原理计算方法，对纯LiMgN，Cu掺杂LiMgN，以及Li过量和不足时Cu掺杂LiMgN体系进行几何结构优化，计算并分析体系的电子结构、半金属性、形成能及光学性质.结果表明，Cu掺入使体系产生自旋极化杂质带，表现出半金属性，且体系性质受Li计量数的影响.当Li不足时体系的杂质带宽度增大，半金属性增强，净磁矩增大，同时体系的形成能降低，居里温度提高.而当Li过量时，体系半金属性消失，但带隙值减小，导电能力增强.通过比较光学性质发现，Cu掺入后体系在低能区出现新的介电峰，且当Li不足时介电峰增强，同时复折射率函数也发生明显变化，体系对低频电磁波吸收加强.

Cu掺杂LiMgN；电子结构；光学性质；第一性原理

来源出版物：科学通报，2015，60（9）： 830-837联系邮箱：毋志民，zmwu@cqnu.edu.cn

封面介绍：The tophat laser beam has near-uniform intensity within a circular disk. Laser beams with such flat-top transversal profile are widely utilized in industry and high power laser systems. Such beams are often generated by the conversion of Gaussian mode with a diffractive optical element. In the cover story of this issue，researchers constructed a laser beam shaping system utilizing the digital micro-mirror device（DMD）. With pulse width modulation，the DMD could be configured to work as an amplitude spatial light modulator. The produced system not only improves the efficiency of DMD-based amplitude modulation regime，but also diversified the laser beams shaping system. This is an easy and flexible method to redistribute the irradiance of the laser beam. As a demonstration，the super-Gaussian beam has been successfully shaped from the Gaussian beam with the DMD. A modal determination method was developed for mode analysis of the created flat-top beams. The DMD-based tophat beam shaping technique will be potentially applied in lithography，ultra-high resolution microscopy，and high energy physics（See the article No. 034202 by DING Xiangyu et al.）.

Shaping super-Gaussian beam through digital micro-mirror device

DING Xiangyu，REN Yuxuan，LU Rongde，et al.

We have set up a novel system for shaping the Gaussian laser beams into super-Gaussian beams. The digital micro-mirror device（DMD）is able to modulate the laser light spatially through binary-amplitude modulation mechanism. With DMD，the irradiance of the laser beam can be redistributed flexibly and various beams with different intensity distribution can be produced. A super-Gaussian beam has been successfully shaped from the Gaussian beam with the use of DMD. This technique will be widely applied in lithography，quantum emulation and holographic optical tweezers which require precise control of beam profile.

laser beam shaping； spatial light modulator； binary optics； DMD； Gamma curve correction