封面文章

物理學(xué)

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

封面介紹：在半導(dǎo)體中注入自旋形成兼具電荷屬性和自旋特性的稀磁半導(dǎo)體可以制成自旋閥、自旋二極管、高密度非易失性存儲(chǔ)器以及磁感應(yīng)器等新型的功能器件，具有誘人的應(yīng)用前景.但是向傳統(tǒng)的Ⅲ-Ⅴ族化合物半導(dǎo)體中摻雜存在兩點(diǎn)不足.首先，傳統(tǒng)的稀磁半導(dǎo)體在引入自旋的同時(shí)也引入了載流子，這種自旋和電荷的捆綁效應(yīng)嚴(yán)重制約了電性和磁性的調(diào)控維度.其次，基于摻雜中的不等價(jià)代替導(dǎo)致磁性離子化學(xué)溶解度嚴(yán)重受限，平均溶解度不足 1%，僅可形成亞穩(wěn)態(tài)薄膜材料.而Ⅰ-Ⅱ-Ⅴ族基新型稀磁半導(dǎo)體 Li（Mg，Cu）N，在Mg2+位引入Cu2+，可以使體系產(chǎn)生半金屬鐵磁性.載流子濃度則通過(guò)改變Li的含量來(lái)進(jìn)行調(diào)控，這樣就實(shí)現(xiàn)了稀磁半導(dǎo)體電性和磁性的分離調(diào)控.而且等價(jià)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(tǒng)稀磁半導(dǎo)體的不足.封面顯示的是通過(guò)改變Li的含量調(diào)控Cu摻雜LiMgN體系性能的晶體結(jié)構(gòu).詳見(jiàn)鄧軍權(quán)等人文（p830）.

新型稀磁半導(dǎo)體Cu摻雜LiMgN的電子結(jié)構(gòu)和光學(xué)性質(zhì)

鄧軍權(quán)，毋志民，楊武慶，等

采用基于密度泛函理論的第一性原理計(jì)算方法，對(duì)純LiMgN，Cu摻雜LiMgN，以及Li過(guò)量和不足時(shí)Cu摻雜LiMgN體系進(jìn)行幾何結(jié)構(gòu)優(yōu)化，計(jì)算并分析體系的電子結(jié)構(gòu)、半金屬性、形成能及光學(xué)性質(zhì).結(jié)果表明，Cu摻入使體系產(chǎn)生自旋極化雜質(zhì)帶，表現(xiàn)出半金屬性，且體系性質(zhì)受Li計(jì)量數(shù)的影響.當(dāng)Li不足時(shí)體系的雜質(zhì)帶寬度增大，半金屬性增強(qiáng)，凈磁矩增大，同時(shí)體系的形成能降低，居里溫度提高.而當(dāng)Li過(guò)量時(shí)，體系半金屬性消失，但帶隙值減小，導(dǎo)電能力增強(qiáng).通過(guò)比較光學(xué)性質(zhì)發(fā)現(xiàn)，Cu摻入后體系在低能區(qū)出現(xiàn)新的介電峰，且當(dāng)Li不足時(shí)介電峰增強(qiáng)，同時(shí)復(fù)折射率函數(shù)也發(fā)生明顯變化，體系對(duì)低頻電磁波吸收加強(qiáng).

Cu摻雜LiMgN；電子結(jié)構(gòu)；光學(xué)性質(zhì)；第一性原理

來(lái)源出版物：科學(xué)通報(bào)，2015，60（9）： 830-837聯(lián)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