The finite-frequency transport properties of a large-spin molecule attached to ferromagnetic contacts are studied theoretically in the Kondo regime. The focus is on the behavior of the dynamical conductance in the linear response regime, which is determined by using the numerical renormalization group method. It is shown that the dynamical conductance depends greatly on the magnetic configuration of the device and intrinsic parameters of the molecule. In particular, conductance exhibits characteristic features for frequencies corresponding to the dipolar and quadrupolar exchange fields resulting from the presence of spin-dependent tunneling. Moreover, a dynamical spin accumulation in the molecule, associated with the off-diagonal-in-spin component of the conductance, is predicted. This spin accumulation becomes enhanced with increasing the spin polarization of the leads, and it results in a nonmonotonic dependence of the conductance on frequency, with local maxima occurring for characteristic energy scales.
We present an original method to estimate the conductivity of a single molecule anchored to nanometric-sized metallic electrodes, using a Mechanically Controlled Break Junction (MCBJ) operated at room temperature in liquid. We record the conductance through the metal / molecules / metal nanocontact while keeping the metallic electrodes at a fixed distance. Taking advantage of thermal diffusion and electromigration, we let the contact naturally explore the more stable configurations around a chosen conductance value. The conductance of a single molecule is estimated from a statistical analysis …
We investigate gold-4,4'-bipyridine-gold single-molecule junctions with the mechanically controllable break junction technique at cryogenic temperature ($T=4.2\,\text{K}$). We observe bistable probabilistic conductance switching between the two molecular binding configurations, influenced both by the mechanical actuation, and the applied voltage. We demonstrate that the relative dominance of the two conductance states is tunable by the electrode displacement, whereas the voltage manipulation induces an exponential speedup of both switching times. The detailed investigation of the voltage-tunab…
If simple guidelines could be established for understanding how quantum interference (QI) can be exploited to control the flow of electricity through single molecules, then new functional molecules, which exploit room-temperature QI could be rapidly identified and subsequently screened. Recently it was demonstrated that conductance ratios of molecules with aromatic cores, with different connectivities to electrodes, can be predicted using a simple and easy-to-use 'magic number theory'. In contrast with counting rules and 'curly-arrow' descriptions of destructive QI, magic number theory capture…
The appealing feature of molecular electronics is the possibility of exploiting functionality built within a single molecule. This functionality can be employed, for example, for sensing or switching purposes. Thus, ideally, the associated conductance changes should be sizable upon application of external stimuli. Here, we show that a molecular spring can be mechanically compressed or elongated to tune its conductance by up to an order of magnitude by controlling the quantum interference between electronic pathways. Oscillations in the conductance occur when the stress built up in the molecule…
We explore the merits of neural network boosted, principal-component-projection-based, unsupervised data classification in single-molecule break junction measurements, demonstrating that this method identifies highly relevant trace classes according to the well-defined and well-visualized internal correlations of the dataset. To this end, we investigate single-molecule structures exhibiting double molecular configurations, exploring the role of the leading principal components in the identification of alternative junction evolution trajectories. We show how the proper principal component proje…
The interplay between groups of water molecules and single-atom contacts, as reflected in the electrical conductances and mechanical forces of copper atomic junctions, is explored by means of first-principles theory and semi-empirical calculations. We study the influence of the atomic geometries of copper electrodes with pyramidal and non-crystalline structures in the presence and absence of water on the conductance profiles as the electrodes approach each other. It is shown that the atomic arrangements of nano-contacts have crucial effects on the formation of plateaus and the conductance valu…
Spin-crossover (SCO) molecules are versatile magnetic switches with applications in molecular electronics and spintronics. Downscaling devices to the single-molecule level remains, however, a challenging task since the switching mechanism in bulk is mediated by cooperative intermolecular interactions. Here, we report on electron transport through individual Fe-SCO molecules coupled to few-layer graphene electrodes \textit{via} $π- π$ stacking. We observe a distinct bistability in the conductance of the molecule and a careful comparison with density functional theory (DFT) calculations allows t…
The shot noise of the current $I$ through junctions to single trioxatriangulenium cations (TOTA$^+$) on Au(111) is measured with a low temperature scanning tunneling microscope using Au tips. The noise is significantly reduced compared to the Poisson noise power of $2eI$ and varies linearly with the junction conductance. The data are consistent with electron transmission through a single spin-degenerate transport channel and show that TOTA$^+$ in a Au contact does not acquire an unpaired electron. Ab initio calculations reproduce the observations and show that the current involves the lowest u…
Understanding the formation of metal-molecule contact at the microscopic level is the key towards controlling and manipulating atomic scale devices. Employing two isomers of bipyridine, $4, 4^\prime$ bipyridine and $2, 2^\prime$ bipyridine between gold electrodes, here, we investigate the formation of metal-molecule bond by studying charge transport through single molecular junctions using a mechanically controlled break junction technique at room temperature. While both molecules form molecular junctions during the breaking process, closing traces show the formation of molecular junctions una…
First-principles many-body calculations of electronic conduction in thiol- and amine-linked molecules
通过硫醇，硫醇盐，和氨基锚定基团连接到金电极的苯分子的电子电导计算使用非平衡格林函数与完全自洽GW近似相结合。计算的苯二硫醇和苯二胺的电导比标准密度泛函理论（DFT）预测的低5倍，与实验非常吻合。相比之下，广泛研究的苯二硫醇盐结构被发现由于不饱和硫键而具有显著更高的电导率。这些研究结果表明，更复杂的金/硫醇盐结构，其中硫醇盐锚被化学钝化的Au吸附原子负责测量的电导。用DFT、Hartree-Fock和GW方法分析得到的能级排列，揭示了分子自相互作用修正（交换）和金属-分子界面动力学屏蔽的重要性。GW自能的主要作用是重整化能级位置，但它对分子共振态形状的影响也影响电导。从DFT或Hartree-Fock开始的非自洽G 0 W 0计算，产生自洽GW结果的50%内的电导值。
Amine-Linked Single Molecule Circuits: Systematic Trends Across Molecular Families
一个全面的审查提出了单分子结电导测量跨家庭的分子测量，而打破了金点接触的分子与胺端基的解决方案。一个理论框架统一的图片胺-金链接键和隧道耦合通过结使用密度泛函理论为基础的计算。许多分子的可再现的电特性和效用被证明是由于金电极和胺连接基团之间的选择性结合，通过供体-受体键欠配位的金原子。虽然键能是适度的，但结所承受的最大力与断开金点接触所需的力相当，但小于所述力。计算出的隧道耦合提供了电导趋势的所有41分子测量在这里，以及洞察电导的变化，由于分子内的构象变化与扭转自由度。计算出的趋势同意的电导范围从10-7 G 0到10-2 G 0，其中G 0是量子的电导（2 e2/h）的测量值的两个因素。
Effective level attraction and magnetic flux-induced negative differential conductance in two double quantum dot molecules embedded in an Aharonov-Bohm ring
Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ
我们描述了一种含有$π$ -扩展的四硫富瓦烯（exTTF）基团的分子线及其与F4 TCNQ的电荷转移复合物的合成和单分子电输运性质。我们使用自制的扫描隧道显微镜使用原位断裂结技术形成单分子结，电导范围在10 G $_{0}$到10 $^{-7}$ G $_{0}$之间。在这个范围内，我们没有观察到一个明确的中性母体分子的电导签名，这表明它的电导太低，或它不形成稳定的连接。相反，我们在对电荷转移复合物进行的实验中确实发现了明确的电导特征。由于我们预期这种物质具有比中性分子更高的电导率，我们相信这支持了中性分子的电导非常低的想法，低于我们的测量灵敏度。我们的理论计算进一步证实了这一点。据我们所知，这是首次报道的单分子电导测量的分子电荷转移物种。
Destructive quantum interference (DQI) and its effects on electron transport is studied in chemical molecules and finite physical lattices that can be described by a discrete Hamiltonian. Starting from a bipartite system whose conductance zeros are known to exist between any two points of a specially designated set, the interference set, we use the Dyson equation to develop a general algorithm of determining the zero conductance points in complex systems, which are not necessarily bipartite. We illustrate this procedure as it applies to the fulvene molecule. The stability of the conductance ze…
We theoretically investigate the electron transport in armchair and zigzag graphene nanoribbons (GNRs) chemically functionalized with p-polyphenyl and polyacene groups of increasing length. Our nearest-neighbor tight-binding calculations indicate that, depending on whether the number of aromatic rings in the functional group is even or odd, the resulting conductance at energies matching the energy levels of the corresponding isolated molecule are either unaffected or reduced by exactly one quantum as compared to the pristine GNR, respectively. Such an even-odd effect is shown to originate from…
