物理學

封面文章

物理學

來源出版物：SCIENCE CHINA Physics，Mechanics & Astronomy，2015，58（3）： 034202聯系郵箱：REN Yuxuanyxren@ustc.edu.cn

封面介紹：在半導體中注入自旋形成兼具電荷屬性和自旋特性的稀磁半導體可以制成自旋閥、自旋二極管、高密度非易失性存儲器以及磁感應器等新型的功能器件，具有誘人的應用前景.但是向傳統的Ⅲ-Ⅴ族化合物半導體中摻雜存在兩點不足.首先，傳統的稀磁半導體在引入自旋的同時也引入了載流子，這種自旋和電荷的捆綁效應嚴重制約了電性和磁性的調控維度.其次，基于摻雜中的不等價代替導致磁性離子化學溶解度嚴重受限，平均溶解度不足 1%，僅可形成亞穩態薄膜材料.而Ⅰ-Ⅱ-Ⅴ族基新型稀磁半導體 Li（Mg，Cu）N，在Mg2+位引入Cu2+，可以使體系產生半金屬鐵磁性.載流子濃度則通過改變Li的含量來進行調控，這樣就實現了稀磁半導體電性和磁性的分離調控.而且等價摻雜可以使得體系具有較高的Cu固溶度，從而使體系居里溫度提高，很好地克服了傳統稀磁半導體的不足.封面顯示的是通過改變Li的含量調控Cu摻雜LiMgN體系性能的晶體結構.詳見鄧軍權等人文（p830）.

新型稀磁半導體Cu摻雜LiMgN的電子結構和光學性質

鄧軍權，毋志民，楊武慶，等

采用基于密度泛函理論的第一性原理計算方法，對純LiMgN，Cu摻雜LiMgN，以及Li過量和不足時Cu摻雜LiMgN體系進行幾何結構優化，計算并分析體系的電子結構、半金屬性、形成能及光學性質.結果表明，Cu摻入使體系產生自旋極化雜質帶，表現出半金屬性，且體系性質受Li計量數的影響.當Li不足時體系的雜質帶寬度增大，半金屬性增強，凈磁矩增大，同時體系的形成能降低，居里溫度提高.而當Li過量時，體系半金屬性消失，但帶隙值減小，導電能力增強.通過比較光學性質發現，Cu摻入后體系在低能區出現新的介電峰，且當Li不足時介電峰增強，同時復折射率函數也發生明顯變化，體系對低頻電磁波吸收加強.

Cu摻雜LiMgN；電子結構；光學性質；第一性原理

來源出版物：科學通報，2015，60（9）： 830-837聯系郵箱：毋志民，zmwu@cqnu.edu.cn

封面介紹：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