Magnetic field induced helical mode and topological transitions in a quasi-ballistic topological insulator nanoribbon with circumferentially quantized surface state sub-bands
Luis A. Jauregui, Michael T. Pettes, Leonid P. Rokhinson, Li Shi, Yong P. Chen
拓扑绝缘体（TI）纳米线（NW）的核心是绝缘的，二维自旋螺旋狄拉克费米子拓扑表面态（TSS）被周向量子化为一系列一维子带，具有新颖的拓扑物理和应用前景。通过芯部的轴向磁通量（Φ）驱动表面子带中的周期性拓扑转变，从具有整数倍带隙的狄拉克点（DP）的全部双简并转变为具有整数倍带隙的狄拉克点（DP）。（包括零）通量量子（Φ $_0$ = h/e，其中h是普朗克常量，e是电子电荷），以包含拓扑保护的，在半整数通量量子处具有恢复DP的非简并1D自旋螺旋模式。预测所得到的磁导表现出Aharonov-Bohm振荡（ABO），其最大值交替地发生在半整数或整数通量量子处（称为π-ABO或0-ABO），这取决于费米波矢量（k $_F$，周期为2π/C，C为NW周长）。在这里，我们报告了在Bi $_2$ Te $_3$ TI纳米晶体中0-ABO和π-ABO之间的这种k $_F$ -周期性交替的清楚观察（NR，矩形横截面NW）场效应器件，其在~2 μm上表现出准弹道输运（如长度无关电导，ABO振幅随温度（T）升高呈指数衰减，以及所提取的相位相干长度的1/T依赖性）。在半通量量子和零通量量子下，作为栅极电压的函数的电导也表现出明显的反相关振荡，其周期为k $_F$（周期为2π/C，当C包围费米波长2π/k $_F$的整数倍时等效），与周向量子化的表面子带一致。我们还提取了最小的费米能量和动量TSS出现的体价带，与已知的Bi $_2$ Te $_3$能带结构。
英文摘要：
A topological insulator (TI) nanowire (NW), where the core is insulating and the 2D spin-helical Dirac fermion topological surface states (TSS) are circumferentially quantized into a series of 1D sub-bands, promises novel topological physics and applications. An axial magnetic flux (Φ) through the core drives periodic topological transitions in the surface sub-bands, changing from being all doubly-degenerate with a gapped Dirac point (DP) at integer (including zero) flux quanta (Φ$_0$ = h/e, with h being the Planck constant and e the electron charge), to contain a topologically-protected, non-degenerate 1D spin helical mode with restored DP at half-integer flux quanta. The resulting magnetoconductance is predicted to exhibit Aharonov-Bohm oscillations (ABO) with maxima occurring alternatively at half-integer or integer flux quanta (referred to as π-ABO or 0-ABO), depending periodically on the Fermi wavevector (k$_F$, with period 2π/C, C being the NW circumference). Here, we report a clear observation of such k$_F$-periodic alternations between 0-ABO and π-ABO in Bi$_2$Te$_3$ TI nanoribbon (NR, a rectangular cross sectional NW) field effect devices, which exhibit quasi-ballistic transport over ~2 μm (as manifested in length-independent conductance, exponential decaying ABO amplitude with increasing temperature (T), and an 1/T dependence of the extracted phase coherence length). The conductances as functions of the gate voltage at half and zero flux quanta also exhibit clear, but anti-correlated oscillations periodic in k$_F$ (with period 2π/C, equivalently when C encloses an integer multiples of Fermi wavelength 2π/k$_F$), consistent with the circumferentially quantized surface sub-bands. We also extract the minimal Fermi energy and momentum for TSS to emerge out of the bulk valence band, in agreement with the known Bi$_2$Te$_3$ bandstructure.
Spin-dependent ballistic transport properties and electronic structures of pristine and edge-doped zigzag silicene nanoribbons: large magnetoresistance
Performance Analysis of Boron Nitride Embedded Armchair Graphene Nanoribbon MOSFET with Stone Wales Defects
研究了石墨烯-氮化硼（GNR-BN）扶手椅型纳米晶（a-GNR-BN）MOSFET在其弹道输运极限下的性能。我们考虑了BN原子嵌在GNR两侧{每侧2，4，6个BN}的a-GNR-BN的三种几何构型3 p，3 p +1和3 p +2。利用密度泛函理论{DFT}对这些H钝化结构的带隙、有效质量和态密度等材料性质进行了计算。利用这些材料参数，在非平衡格林函数（NEGF）形式下进行了自洽Poisson-Schrodinger模拟，计算了弹道MOSFET器件的特性。对于宽度约为5 nm的混合纳米管，发现模拟的导通电流在276 uA - 291 uA的范围内，对于VDD = 0.68 V，导通/关断比为7.1 x 10^6 - 7.4 x 10^6，对应于10 nm技术节点。我们进一步研究了随机分布的Stone Wales {SW}缺陷在这些混合结构中的影响，并且对于6.35%的SW缺陷密度，仅观察到2.52%的导通电流退化。
Unambiguous Simulation of Diffusive Charge Transport in Disordered Nanoribbons
Centro de Física das Universidades do Minho e do Porto (CF-UM-UP) and Laboratório de Física para Materiais e Tecnologias Emergentes LaPMET, University of Porto（波尔图大学及米尼奥大学物理中心与新兴材料与技术物理实验室）；Institute for Systems and Computer Engineering, Technology and Science (INESC TEC)（系统、计算机工程、技术与科学研究所）；Department of Materials, Imperial College London（帝国理工学院材料系）
Pseudo-ballistic transport in 3D topological insulator quantum wires
研究了无序三维拓扑绝缘体量子线中的量子电导涨落。实验和理论都揭示了介观导体中一种新的输运机制，即伪弹道输运，其弹道性质持续超过输运平均自由程，具有扩散输运的特征。由于准1D表面模式，其导致非通用电导波动，如在长且窄的Bi $_2$ Se $_3$纳米带中所观察到的。量子线中的自旋螺旋狄拉克费米子由于强的量子限制和弱的动量散射而在异常宽的能量范围内保持伪弹道性质。
Impact of Valley Degeneracy on Thermoelectric Properties of Zigzag Graphene Nanoribbons with Staggered Sublattice Potentials and Transverse Electric Fields
Quantized Conductance through Surface States in High Quality Three-Dimensional Dirac Semimetal Cd$_3$As$_2$ Nanowire/Nanoribbon p-n Junctions
DGIST Research Institute, DGIST（大邱科学技术院研究学院）；Electrical and Computer Engineering, National University of Singapore（新加坡国立大学电气与计算机工程系）；Department of Physics, KTH Royal Institute of Technology（皇家理工学院物理系）；Industrial AX Innovation Research Institute and Sensor Technology Support Center, DGIST（大邱科学技术院工业AX创新研究所及传感器技术支持中心）；Department of Advanced Materials Chemistry, Korea University（韩国大学先进材料化学系）；Department of Physics and Chemistry, DGIST（大邱科学技术院物理化学系）；Department of Interdisciplinary Engineering, DGIST（大邱科学技术院交叉工程学系）；Institute of next generation semiconductor technology (INST), DGIST（大邱科学技术院下一代半导体技术研究所）
Observation of the superconducting proximity effect and possible evidence for Pearl vortices in a candidate topological insulator
我们报道了超导邻近效应的观察在纳米带的候选拓扑绝缘体（Bi 2 Se 3），这是与超导（钨）接触接口。我们观察到一个超导和多个Andreev反射的通道长度比推导出正常状态运输的非弹性和扩散的热长度长得多。这表明邻近效应优先耦合到弹道表面传输通道，即使在共存的扩散体通道的存在下。当一个磁场垂直于纳米晶的平面施加时，我们观察到在磁场中周期性的磁阻振荡。定量比较与模型的涡旋封锁有关的珍珠涡的形成在该地区的邻近诱导超导性的发生这些振荡。
Quantized conductance in a CVD-grown nanoribbon with hidden Rashba effect
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）；University of Chinese Academy of Sciences（中国科学院大学）；Hefei National Laboratory（合肥国家实验室）
