The spontaneous fluorescence rates of single-molecule emitters are typically on the order of nanoseconds. However coupling them with plasmonic nanostructures can substantially increase their fluorescence yields. The confinement between the tip and sample of a scanning tunneling microscope creates a tunable nanocavity, an ideal platform for exploring the yields and excitation decay rates of single-molecule emitters depending on the coupling strength to the nanocavity. With this setup we estimate the excitation lifetimes from the direct time-resolved measurements of the fluorescence decays of phthalocyanine adsorbates, decoupled from the metal substrates by ultrathin NaCl layers. It is found that nanosecond-range lifetimes prevail for the emitters away from the nanocavity, whereas for the tip approached to a molecule, we find a substantial effect of the nanocavity coupling, which reduces the lifetimes to a few picoseconds. An analysis is performed to investigate the crossover between the far-field and tip-enhanced photoluminescence regimes. This approach overcomes the drawbacks associated with the estimation of lifetimes for single molecules from their respective emission linewidths.
Probing up-conversion electroluminescence of decoupled porphyrin molecules in a plasmonic nanocavity
Max-Planck-Institut für Festkörperforschung（马克斯·普朗克固体研究所）；Institut de Physique, École Polytechnique Fédéral Lausanne（洛桑联邦理工学院物理研究所）；Gleb Wataghin Institute of Physics - University of Campinas - UNICAMP（坎皮纳斯大学格莱布·瓦塔金物理研究所）；Nanjing University（南京大学）
Tunable high speed atomic rotor in Bi$_{2}$Se$_{3}$ revealed by current noise
使用扫描隧道显微镜（STM）操纵单个原子和分子的能力对于开发从纳米级电机和开关到量子计算机的大量原子级设备和结构至关重要。特别是分子马达由于其组装成复杂的纳米级机器的潜力而吸引了相当大的关注。尽管被操纵的原子或分子通常在衬底的顶部上，但是嵌入在晶格中的马达对于自下而上构造可以是非常有益的，并且可以另外用于探测晶格对主体材料的电子性质的影响。在这里，我们提出了控制操纵的转子在Fe掺杂Bi $_{2}$ Se $_{3}$的发现。我们发现，进入转子的电流，这可以与电压微调，驱动三个等效方向之间的全方位切换，其中每个可以冻结在小偏置电压。使用在1MHz的电流波动测量和模型模拟，我们估计，子nA电流的开关速率达到数百kHz。
Quantum-spin-Hall insulator with a large gap: single-layer 1T' WSe$_2$
二维（2D）拓扑绝缘体（TI）是基于量子自旋霍尔（QSH）效应的低耗散自旋电子器件的有前途的平台，但实验实现具有适合于室温应用的大带隙的此类系统已被证明是困难的。在这里，我们报告了在双层石墨烯上成功生长的具有1 T '结构的准独立WSe $_2$单层，其不存在于WSe $_2$的本体形式中。利用角分辨光电子能谱（ARPES）和扫描隧道显微镜/能谱（STM/STS），我们在1 T '层中观察到一个129 meV的能隙和一个位于层边界附近的能隙边缘态。通过第一性原理计算证实了系统的二维TI特性。所观察到的间隙减小掺杂Rb吸附，最终导致绝缘体-半金属过渡。这种具有可调带隙的大间隙2D TI的发现为开发先进的纳米级系统和量子器件提供了机会。
