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封面文章 Hongtao Yan(闫宏涛), Qiang Gao(高强), Chunyao Song(宋春尧), Chaohui Yin(殷超辉), Yiwen Chen(陈逸雯), Fengfeng Zhang(张丰丰), Feng Yang(杨峰), Shenjin Zhang(张申金), Qinjun Peng(彭钦军), Guodong Liu(刘国东), Lin Zhao(赵林), Zuyan Xu(许祖彦), and X. J. Zhou(周兴江) Chin. Phys. B, 2022, 31 (8): 087401 文章亮点介绍 铜氧化物高温超导体在正常态表现出许多奇特的物理性质,其中一个最突出的反常特征是赝能隙的存在,即在超导转变温度Tc和赝能隙转变温度T*之间存在能隙。揭示赝能隙的物理本质及其与超导电性之间的关系是高温超导研究中的核心问题。关于赝能隙的起源至今仍然存在争议,可能的原因主要包括电子预配对或者来源于一些竞争序。其中,电子预配对表现为粒子-空穴对称性守恒,而竞争序则可能导致粒子-空穴对称性破缺。因此,研究铜氧化物高温超导体在赝能隙态的粒子-空穴对称性对理解赝能隙的起源具有重要意义。 本文作者通过高分辨率激光角分辨光电子能谱仪对最佳掺杂的Bi2Sr2CuO6超导体(Tc=32 K)进行测量,发现费米面的拓扑结构和能带结构在T*温度(T*~150 K)上下没有出现突然的变化,在超导态和赝能隙态沿整个费米面的电子结构和能隙结构均满足粒子-空穴对称性。这一结果表明,在最佳掺杂铜氧化物高温超导体的赝能隙态,粒子-空穴对称性保持守恒,为理解赝能隙的起源及其与高温超导电性之间的关系提供了重要的实验证据。 原文链接 PDF Fig. 1. Fermi surface mappings of the optimally-doped Bi2Sr2CuO6+δsuperconductor measured at different temperatures. (a1)–(a5) Fermi surface mappings near the nodal region measured at 200 K (a1), 140 K (a2), 90 K (a3), 40 K (a4) and 20 K (a5). (b1)–(b5) Same as (a1)–(a5), but measured near the antinodal region. The measured main Fermi surface is marked by red lines. 亮点文章 Jiahao Yuan(袁嘉浩), Mengzhou Liao(廖梦舟), Zhiheng Huang(黄智恒), Jinpeng Tian(田金朋), Yanbang Chu(褚衍邦), Luojun Du(杜罗军), Wei Yang(杨威), Dongxia Shi(时东霞), Rong Yang(杨蓉), and Guangyu Zhang(张广宇) Chin. Phys. B, 2022, 31 (8): 087302 文章亮点介绍 二维莫尔超晶格体系由于其新颖的物理特性,吸引了人们越来越多的关注,并开辟出了一个全新的研究领域——转角电子学。尽管这一领域的研究已取得了一定的成果,但精确且可重复地控制样品的层间转角仍然是困扰其发展的一个难题。 本文提出了一种利用原子力显微镜针尖操纵技术来精确控制外延二硫化钼/石墨烯异质结层间转角的方法。在固定二硫化钼的一角作为支点的情况下,通过精确操纵针尖的移动路径,带动二硫化钼远离支点的一端移动,实现了层间转角的可控调控。控制精度可以小于0.1°。导电原子力显微镜扫描显示了层间转角对二硫化钼/石墨烯异质结莫尔超晶格周期的影响,光谱学表征验证了转角对该体系声子和激子的调制。本工作提供了一种精确控制二维莫尔材料层间转角的技术,使莫尔物理转角相图的建立成为可能。 原文链接 PDF Fig. 2. Twist angle control of MoS2/graphene heterostructure. (a) Schematic diagram of the method to control the twist angle between MoS2 and graphene by an AFM tip. (b)–(d) A demonstration of precise control of interlayer twist angle below 0.1°. (e)–(h) AFM images of MoS2/graphene heterostructure at different twist angles we want. 亮点文章 Adaptive semi-empirical model for non-contact atomic force microscopy Xi Chen(陈曦), Jun-Kai Tong(童君开), and Zhi-Xin Hu(胡智鑫) Chin. Phys. B, 2022, 31 (8): 088202 文章亮点介绍 非接触原子力显微镜(nc-AFM)是一种以原子分辨率研究表面形貌的强大工具,对比理论模拟的图像可以更好地分析表面原子结构。密度泛函理论(DFT)计算虽然能够准确估计针尖与样品间的受力,但是模拟整个图像需要的计算量十分庞大。通过一些简化近似可大幅减少计算量,但同时会造成模拟图像失真。本文设计了一种结合半经验模型与DFT计算模拟nc-AFM图像方法。只需要给定样品原子结构的电荷密度分布,以及少量DFT计算得到的针尖与样品间受力数据点,就可以生成准确的模拟图像。 我们以一些具有代表性的有机分子—金属吸附体系作为研究对象,比较该方法与全DFT计算结果,发现预测的针尖受力曲线十分接近,但模拟整个图像的计算量小四个数量级。该方法可以广泛应用于化学惰性或非惰性的功能化针尖,在样品分子的元素识别方面也较有优势。总体而言,使用这一方法可以高效地辅助AFM观测进行原子结构预测,对于进一步探索AFM成像机制也会有帮助。 原文链接 PDF Fig. 4. FAST-AFM simulations for pentacene/Cu(111) with CuCO tip. (a) Simulated frequency shift image without tilting correction. Tip height is 3.8 Å. (b) Experimental image with CO-functionalized tip. (c)Simulated frequency shift image with tilting correction at Z = 3.8 Å. (d) Simulated force curves (dashed lines) verses DFT calculations (dots) at crucial positions. 亮点文章 Monolayer MoS2 of high mobility grown on SiO2 substrate by two-step chemical vapor deposition Jia-Jun Ma(马佳俊), Kang Wu(吴康), Zhen-Yu Wang(王振宇), Rui-Song Ma(马瑞松), Li-Hong Bao(鲍丽宏), Qing Dai(戴庆), Jin-Dong Ren(任金东), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2022, 31 (8): 088105 文章亮点介绍 MoS2作为最具典型的二维半导体材料,实现高质量和大面积生长,是能够将其应用于集成电路中,延续摩尔定律的关键。本文发展了一种两步常压化学气相沉积在SiO2衬底上生长单层MoS2的方法,晶体尺寸达到110 μm。结合四探针STM表征、两端场效应器件输运测量和直接的四端范德堡法输运测量,验证了SiO2衬底上生长的MoS2具有高的质量和迁移率。该工作的亮点在于:(1)首次使用云母上生长的具有大的比表面积的MoO3纳米片作为MoS2生长的Mo源,采用face-to-face的衬底和源的放置构型,为MoS2生长探索了一种新的方式;(2)生长的MoS2晶体直接通过四探针STM获得了室温下的原子分辨图像,并结合STS谱获得了晶体的带隙;(3)对比了SiO2衬底上两端MOSFET的迁移率和范德堡构型的四端场效应迁移率,由于消除了接触电阻的影响,范德堡构型的迁移率达到了28.4 cm2·V-1·s-1。 本文提供了一种两步法生长MoS2的方法,由于采用的是face-to-face的放置方式,使得MoS2的生长尺寸仅受限于云母上MoO3的分布区域,为进一步合成大面积晶圆尺寸MoS2提供了重要参考。 原文链接 PDF Fig. 1. Synthesis of the CVD-grown monolayer MoS2. (a) Schematic illustration of the two-step CVD process. The MoO3 crystal is grown on the mica substrate during the first step. Then the monolayer MoS2 crystal is synthesized on the SiO2 substrate by using the first-step product, i.e., MoO3 single crystal, as the Mo source. (b) Large-area optical image of the MoO3 on the mica substrate in the first-step CVD process. (c)–(e) Large-scale optical images of the MoS2 products at different growth temperatures of 800 °C (c), 850 °C, (d) and 900 °C (f), respectively. 亮点文章 Two-dimensional Sb cluster superlattice on Si substrate fabricated by a two-step method Runxiao Zhang(张润潇), Zi Liu(刘姿), Xin Hu(胡昕), Kun Xie(谢鹍), Xinyue Li(李新月), Yumin Xia(夏玉敏), and Shengyong Qin(秦胜勇) Chin. Phys. B, 2022, 31 (8): 086801 文章亮点介绍 团簇是一种介于微观原子、分子与宏观材料的物质状态,一直以来是凝聚态物理研究的热点之一。团簇以规则的形式排列而成的阵列是人们研究团簇新奇物性的优良平台,因此,研究团簇阵列的生长及物性对团簇科学的研究有着重要的意义。 本文通过一种两步法生长方式,使用分子束外延在硅衬底上制备了规整排布的二维Sb团簇阵列。研究发现3-5个Sb原子组成的三角形、菱形、梯形是Sb团簇最稳定的状态,并通过进一步的谱学测量,在不同的Sb团簇上观测到了明显的单电子隧穿现象。本文的研究提供了一种简单可行的团簇阵列的生长方式,增进了人们对团簇的结构特性及电学特性的理解,并为其在未来单电子器件的应用提供重要参考价值。 原文链接 PDF Fig. 4. STM images of atomic structure of Sb clusters. (a) High resolution STM topography of Sb cluster superlattice. Inset shows the 2D Fourier transform of Fig.3(a). (b) Zoom-in high resolution STM topography of Sb cluster superlattice. (c) Schematics of Sb clusters consisting several Sb atoms ranging from 2 to 7. (d) Statistical distribution of the structures of Sb clusters. Scan sizes are (a) 15 nm × 15 nm, (b) 9 nm × 9 nm. All tunneling parameters are -2.5 V, -200 pA. 亮点文章 Effect of f-c hybridization on the γ→α phase transition of cerium studied by lanthanum doping Yong-Huan Wang(王永欢), Yun Zhang(张云), Yu Liu(刘瑜), Xiao Tan(谈笑), Ce Ma(马策), Yue-Chao Wang(王越超), Qiang Zhang(张强), Deng-Peng Yuan(袁登鹏), Dan Jian(简单), Jian Wu(吴健), Chao Lai(赖超), Xi-Yang Wang(王西洋), Xue-Bing Luo(罗学兵), Qiu-Yun Chen(陈秋云), Wei Feng(冯卫), Qin Liu(刘琴), Qun-Qing Hao(郝群庆), Yi Liu(刘毅), Shi-Yong Tan(谭世勇), Xie-Gang Zhu(朱燮刚), Hai-Feng Song(宋海峰), and Xin-Chun Lai(赖新春) Chin. Phys. B, 2022, 31 (8): 087102 文章亮点介绍 Ce在常压下降温时会发生体积坍缩高达16%的同构相变(γ→α相变),对此相变的理论解释主要为近藤体积坍缩模型,此模型强调相变过程中4f能级(f)与传导(c)电子之间的杂化效应,对Ce单晶薄膜的研究已经揭示了降温时γ-Ce中存在f-c杂化效应。而这一杂化效应对Ce的γ→α相变的影响至今没有被明确验证,因为相变发生在体层中,薄膜表面仍处于γ相。本工作在Ce基体中掺杂不含f电子的La形成较低f电子浓度的CeLa合金薄膜,通过对合金薄膜进行晶体结构、电输运及电子结构表征以及唯象周期性安德森模型和修正的安德森杂质模型理论计算,比较了CeLa合金与纯Ce的f-c杂化效应及γ→α相变程度的强弱。研究发现,La掺杂使Ce的f-c杂化效应减弱,同时使Ce的γ→α相变受到抑制,间接证明了f-c杂化对Ce的γ→α相变的驱动作用。 该工作证明了4f(f)电子和传导(c)电子之间的杂化作用对Ce的γ→α相变的驱动作用,并与其他Ce基合金γ→α相变压力与杂质浓度的研究结果一致,对于进一步研究具有类似相变行为的其他稀土和锕系金属及合金具有重要的参考意义。 原文链接 PDF Fig. 1. (Color online) (a)-(d) Detailed band dispersions of Ce, Ce0.833La0.167, Ce0.638La0.362 and Ce0.383La0.617 thin films along K-Γ-K, in which the f-c hybridization bands are fitted by PAM model. The red dotted lines and green lines are the fitted results, while the black lines are the conduction band dispersions without f-c hybridization. All the PAM fitting results from (a) to (c) are also summarized in (h). (e) Normalized EDCs within ±0.04 Å around the Γ point of the thin films in (a) - (d), together with that of pure La thin film (ARPES spectra not shown here). (f) Normalized EDCs of (a) - (d) in (e) subtracted that of pure La thin films. The spectra are vertically shifted for a better view. (g) Peak areas of 4f15/2 (open squares) and 4f17/2 (open triangles) fitted from (f), together with the fitted indirect hybridization gaps Δg (open circles). 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