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Tunable correlation in twisted monolayer-trilayer graphene
Dongdong Ding(丁冬冬), Ruirui Niu(牛锐锐), Xiangyan Han(韩香岩), Zhuangzhuang Qu(曲壮壮), Zhiyu Wang(王知雨), Zhuoxian Li(李卓贤), Qianling Liu(刘倩伶), Chunrui Han(韩春蕊), and Jianming Lu(路建明)
Chin. Phys. B, 2023, 32 (6): 067204
近年来,摩尔超晶格界面上的电子关联现象如绝缘体、超导、磁性等新奇物性成为研究热点之一,范德瓦尔斯异质结体系亦逐渐从魔角双层石墨烯发展到各种各样的多层结构。不同于前者,多层石墨烯异质结的电子能带结构受垂直电场调控,从而为电场调控各种新奇物性提供了新机遇。
本文首次构筑了转角为1.2°的单层和三层石墨烯异质结并在强磁场和变温条件下开展关联绝缘体的电学输运研究。研究表明,关联绝缘态在导带和价带具有不对称性,并与电位移场密切相关,其根源在于范霍夫奇点。在电位移场-载流子浓度二维相图中,范霍夫奇点表现为纵向电阻峰和零霍尔电阻,其具有类似的导带-价带不对称性并严重依赖电位移场、磁场的调控;当它遇到平带半填充时,高电子态密度带来的电子关联性驱动产生具有能隙的关联绝缘态。同时,利用电阻温度曲线得到的费米速度也验证了导电和价带之间电子关联性的差异。本文的研究有助于我们更加深入地理解摩尔超晶格中的电子关联现象,并推动更丰富的转角堆叠平带体系的深入探索和物性调控研究。
原文链接
Fig. 1. Electronic phase diagram of twisted monolayer-trilayer graphene heterostructure. (a) Schematic of the device with the twist angle θ, where the top and bottom gates are metal and a thin graphite, respectively. (b) Optical characterization with enhanced visibility. Left inset: finished device with indexed electrodes. Right inset: Raman spectra of both Bernal and rhombohedral trilayer graphene. (c) Phase diagram as a function of filling factors ν and displacement field D for the sample between pins 1 and 19. (d) Similar phase diagram for the sample between pins 11 and 13.
Jie Yan(闫杰), Yanpeng Liu(刘彦鹏), Yong Hou(侯永), Cheng Gao(高城), Jianhua Wu(吴建华), Jiaolong Zeng(曾交龙), and Jianmin Yuan(袁建民)
Chin. Phys. B, 2023, 32 (6): 063101
近十年来,X射线自由电子激光(XFEL)开启了光与物质相互作用领域研究的新时代。以斯坦福大学自由电子激光器 LCLS为例,典型的X射线脉冲参数为:光子能量 0.25-12千电子伏,宽度2-100飞秒,峰值光强达1020 W/cm2,亮度大约是同步辐射光源的百万倍。如此超强超快的X射线作用到原子上时,原子的内壳层电子被剥离,在内壳层上产生一个或多个空穴,形成空洞原子。空洞原子处于极端非平衡态,快速地通过俄歇和自发辐射过程衰变,俄歇电子能谱包含了空穴寿命等重要信息。X射线与原子作用时,除了光电离,共振激发对原子状态的演化也非常重要,因为共振激发的截面通常比光电离截面大很多。
本文使用基于细致能级层次的速率方程,模拟了超强超快X射线与氖原子作用时,在光电离和共振激发的综合作用下,产生了1s02s22p6np双空心态,以及该双空心态的弛豫过程,并给出了与实验结果相符的精密俄歇电子能谱。结果表明:俄歇电子能谱的相对强度非常敏感地依赖于X射线光子能量和带宽,这可以作为相关的XFEL实验诊断工具。
原文链接
Fig. 3. Auger electron emission spectra in interaction with x-ray pulses. (a), Auger electron emission spectra contributed by Ne1+ and Ne2+ are shown. (b), the x-ray bandwidth of 4.5 eV is fixed and the x-ray center photon energy is variable. (c), the x-ray center photon energy of 991 eV is fixed and the x-ray bandwidth is variable.
Single-electron transport in H2O@C60 single-molecule transistors
Bowen Liu(刘博文), Jun Chen(陈俊), Yiping Ouyang(欧阳一平), Minhao Zhang(张敏昊), Yuan-Zhi Tan(谭元植), and Fengqi Song(宋凤麒)
Chin. Phys. B, 2023, 32 (6): 063601
晶体管允许施加偏置和栅极电压,已被用来研究单个富勒烯团簇及其衍生物的输运性质。H2O@C60作为一类富勒烯衍生物,为研究水分子的两个不同的核自旋态:邻水(ortho-water)和对水(para-water)提供了理想的“纳米尺度实验平台”。2021年,研究人员测量了单个H2O@C60团簇的隧穿谱,通过将测量的电导峰与理论计算结果进行比较,将电导峰归因于水分子的旋转和振动激发。然而,也有研究人员测量了单个H2O@C60团簇的电导,表明捕获的H2O几乎完全与外场隔离。因此,本文继续尝试研究了单个H2O@C60的电子输运。
本工作首先通过 “分子手术”技术合成了H2O@C60分子,然后用电迁移反馈断结技术制备了H2O@C60单分子晶体管,观察到单电子输运行为。作者利用电容模型计算了H2O@C60单分子晶体管的电容比等参数,发现其比C60单分子晶体管具有更强的栅压调控效率。密度泛函理论计算和之前的研究表明,这一现象可能归因于H2O分子极化所带来的影响。
原文链接
Fig. 1. (a) Representative Isd–Vsd curves after the electromigration for five different gate voltages in an H2O@C60 SMT. The significant difference between the curves indicates the successful manipulation of the molecular chemical potential by gate voltages. (b) Calculated differential conductance dIsd/dVsd as a function of the bias voltage Vsd with various gate voltages Vg using the raw data in (a). (c) Two-dimensional plots of the differential conductance dIsd/dVsd versus the bias voltage Vsd and the gate voltage Vg in H2O@C60 SMTs. We can see the distinct Coulomb diamond patterns, indicated by the black dashed lines. The excitation indicated by the black arrow confirms the presence of the H2O@C60 molecule bridging the junction.
Haimin Zhang(张海民), Dezhi Song(宋德志), Fuyang Huang(黄扶旸), Jun Zhang(仉君), and Ye-Ping Jiang(蒋烨平)
Chin. Phys. B, 2023, 32 (6): 066802
在分子束外延的生长中,衬底表面能、薄膜表面能、界面能等热力学参量决定了特定薄膜在特定衬底上的生长模式:层状生长、岛状生长等等。比如碲薄膜在钛酸锶(001)上的外延生长中,碲和钛酸锶表面的热力学参量导致了在此衬底上无法形成单层的碲薄膜,因此生长模式是岛状生长。这导致之前一直没有均匀厚度超薄碲薄膜生长的报道。本文尝试了一种新的生长模式,这种生长模式可以生长出均匀平铺的多层碲薄膜。这种生长模式可行的本质是可同时形成多层的薄膜,从而改变了常规生长条件下逐层生长的模式,引入了新的热力学成膜条件。这个热力学条件中的新变量是薄膜的层厚,因此成膜有着随层厚的临界行为:只有在特定厚度上才能成膜。
本文阐述了碲在钛酸锶衬底上形成均一薄膜的临界行为,并研究了超薄碲薄膜的电子态特性。实验发现碲薄膜的临界成膜厚度为3个碲单层。扫描隧道谱的测量显示超薄碲薄膜的能隙约为石墨烯衬底上同等厚度薄膜能隙的两倍。本文实现了钛酸锶衬底上均一厚度超薄碲薄膜的生长,这为其他具有类似热力学参量的薄膜和衬底体系中高质量超薄膜的生长提供了可能。
原文链接
Fig. 3. LT growth of 3 ML Te films on STO (001) substrate and the band gap evolution of β-Te films with different thicknesses. (a) and (b) display the RHEED pattern and STM morphology (U = +3 V, It = 10 pA) of 3-ML β-Te after the LT/FA process, respectively. (c) The corresponding atomically resolved STM images (U = +2 V, It = 50 pA). The inserts display the FFT pattern. (d) STS spectra measured on films with various thickness on STO and graphene.
Stochastic fluctuations in the rotation of the bacterial flagellar motor
Guanhua Yue(岳冠骅), Rongjing Zhang(张榕京), and Junhua Yuan(袁军华)
Chin. Phys. B, 2023, 32 (6): 068703
带鞭毛的细菌通过旋转长约10微米的螺旋形鞭毛丝在水中游动,每根鞭毛丝的底部由一个嵌入细胞膜内的鞭毛马达驱动。细菌鞭毛马达是一种纳米级旋转马达,通过产生扭矩来驱动鞭毛丝的旋转。输出扭矩是马达的一个重要特性。通常,马达的旋转是通过将微米级的微珠连接到切短的鞭毛丝上来监测的,并且通过计算液体介质对微珠旋转产生的粘性阻力来提取马达扭矩。
本文探索了一种独立测量马达扭矩的方法,利用涨落定理(Fluctuation Theorem)通过马达旋转速度的热涨落来进行测量。然而,本研究发现热涨落之外还存在巨大的未知涨落,这妨碍了涨落定理的应用。通过进一步对这种涨落的时间尺度和振幅进行表征,发现这可能是由于马达的步进行为引起的扭矩涨落。这里描述的扭矩涨落幅度为马达扭矩生成过程中的相互作用势曲线提供了新的信息,并为进一步利用涨落定理测量马达扭矩指明了实验方向。
原文链接
Fig. 3. (a) An example image of a rotating bead (right) and a stable bead stuck to the cover glass (left) captured by the camera. (b) The rotation trajectory of the rotating bead for 5 seconds, which was corrected for the drift of the sample stage and with the trajectory center moved to (0, 0). (c) The calculated angular speed of this rotation trace section, which has been filtered by running average with a window size of 0.02 s. (d) σϕ2(∆t) as a function of ∆t. The blue solid line is the experimental data, the red dashed line is the linear fitting of the experimental data in the time range of 0.1 s to 0.5 s, the black dashed line is σϕ2(∆t) = 2D0∆t, which is induced by the thermal noise with D0 = kBT/γ, and the yellow dashed line near the x-axis is the σϕ2(∆t) induced by the bending flexibility of the hook and the camera detection noise.
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