Showing papers by "Carmen Herrmann published in 2020"
TL;DR: A symmetry analysis of the key quantities determining transport probabilities of electrons of different spin orientations helps to identify essential constraints in the theoretical description of the CISS effect and draws an analogy with the appearance of imaginary terms in simple models of barrier scattering, which may help understanding the unusually effective long-range electron transfer in biological systems.
Abstract: The chiral-induced spin selectivity (CISS) effect, which describes the spin-filtering ability of diamagnetic structures like DNA or peptides having chiral symmetry, has emerged in the past years as...
63 citations
TL;DR: Although the CISS effect is entirely attributed in the literature to molecular spin filtering, spin-orbit coupling being partially inherited from the metal electrodes plays an important role in the first-principles calculation of the spin polarization in molecular junctions caused by the chiral induced spin selectivity (CISS) effect.
Abstract: We have carried out a comprehensive study of the influence of electronic structure modeling and junction structure description on the first-principles calculation of the spin polarization in molecu...
29 citations
TL;DR: A simple descriptor based on chemical intuition, consisting only of copper-bridge angles and copper-copper distances, clearly outperforms several more sophisticated descriptors when it comes to extrapolating towards larger experimentally relevant complexes, reinforcing the crucial role of choosing a suitable descriptor, and highlighting the interesting question of the role of chemical in-tuition vs. systematic or automated selection of features for machine learning in chemistry.
Abstract: Heisenberg exchange spin coupling between metal centers is essential for describing and understanding the electronic structure of many molecular catalysts, metalloenzymes, and molecular magnets for...
13 citations
TL;DR: In this paper, the local current flow through three small aromatic carbon molecules, namely, benzene, naphthalene, and anthracene, is studied using density functional theory and the nonequilibrium Green's function method for transport.
Abstract: The local current flow through three small aromatic carbon molecules, namely, benzene, naphthalene, and anthracene, is studied. Applying density functional theory and the nonequilibrium Green's function method for transport, we demonstrate that pronounced current vortices exist at certain electron energies for these molecules. The intensity of these circular currents, which appear not only at the antiresonances of the transmission but also in the vicinity of its maxima, can exceed the total current flowing through the molecular junction and generate considerable magnetic fields. The $\ensuremath{\pi}$ electron system of the molecular junctions is emulated experimentally by a network of macroscopic microwave resonators. The local current flows in these experiments confirm the existence of current vortices as a robust property of ring structures. The circular currents can be understood in terms of a simple nearest-neighbor tight-binding H\"uckel model. Current vortices are caused by the interplay of the complex eigenstates of the open system which have energies close to the considered electron energy. Degeneracies, as observed in benzene and anthracene, can thus generate strong circular currents, but also nondegenerate systems like naphthalene exhibit current vortices. Small imperfections and perturbations can couple otherwise uncoupled states and induce circular currents.
13 citations
17 Sep 2020
TL;DR: This article revisited the prototypical Co/Cu(001) Kondo system and showed that different parameterizations of the Coulomb interaction yield different screening properties and Kondo scenarios, and also showed that Kondo can be adapted to different Coulomb interactions.
Abstract: This article revisits the prototypical Co/Cu(001) Kondo system and shows that different parameterizations of the Coulomb interaction yield different screening properties and Kondo scenarios.
11 citations
TL;DR: BO4 is the first compound exhibiting antiferromagnetic ordering among SMMs mediated by π-electrons, demonstrating the synergetic effects between SMMs and molecular conductors.
Abstract: Single-molecule magnets (SMMs) show superparamagnetic behaviour below blocking temperature at the molecular scale, so they exhibit large magnetic density compared to the conventional magnets. Combining SMMs and molecular conductors in one compound will bring about new physical phenomena, however, the synergetic effects between them still remain unexplored. Here we present a layered molecule-based compound, β′′-(BEDO-TTF)4 [Co(pdms)2]·3H2O (BO4), (BEDO-TTF (BO) and H2pdms are bis(ethylenedioxy)tetrathiafulvalene and 1,2-bis(methanesulfonamido)benzene, respectively), which was synthesized by using an electrochemical approach and studied by using crystal X-ray diffraction. This compound simultaneously exhibited metallic conductivity and SMM behaviour up to 11 K for the first time. The highest electrical conductivity was 400–650 S cm−1 at 6.5 K, which is the highest among those reported so far for conducting SMM materials. Furthermore, antiferromagnetic ordering occurred below 6.5 K, along with a decrease in conductivity, and the angle-independent negative magnetoresistance suggested an effective electron correlation between the conducting BO and Co(pdms)2 SMM layers (d–π interactions). The strong magnetic anisotropy and two-dimensional conducting plane play key roles in the low-temperature antiferromagnetic semiconducting state. BO4 is the first compound exhibiting antiferromagnetic ordering among SMMs mediated by π-electrons, demonstrating the synergetic effects between SMMs and molecular conductors.
10 citations
TL;DR: It is shown that for naphthalene‐bridged biscobaltocenes with competing through‐space and through‐bond pathways, the consequences of pinching are far less intuitive: despite the known dominance of through‐ space interactions, the bridge plays a much larger role for exchange spin coupling than previously assumed.
Abstract: Pinching molecules via chemical strain suggests intuitive consequences, such as compression at the pinched site and clothespin-like opening of other parts of the structure. If this opening affects two spin centers, it should result in reduced communication between them. We show that for naphthalene-bridged biscobaltocenes with competing through-space and through-bond pathways, the consequences of pinching are far less intuitive: despite the known dominance of through-space interactions, the bridge plays a much larger role for exchange spin coupling than previously assumed. Based on a combination of chemical synthesis, structural, magnetic, and redox characterization, and a newly developed theoretical pathway analysis, we can suggest a comprehensive explanation for this non-intuitive behavior. These results are of interest for molecular spintronics, as naphthalene-linked cobaltocenes can form wires on surfaces for potential spin-only information transfer.
9 citations
TL;DR: This protocol is based on a combination of density-functional theory with a polarizable continuum model introduced by Kaupp et al. for mixed-valence molecules and can predict the tunneling-to hopping transition length with a maximum error of one subunit in five sets of molecular wires studied experimentally in molecular junctions at room temperature.
Abstract: Understanding charge transport through molecular wires is important for nanoscale electronics and biochemistry. Our goal is to establish a simple first-principles protocol for predicting the charge...
8 citations
Posted Content•
TL;DR: Aiello et al. as mentioned in this paper provide a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects, and present a vision for their future role in enabling room-temperature quantum technologies.
Abstract: Author(s): Aiello, Clarice D; Abbas, Muneer; Abendroth, John; Banerjee, Amartya S; Beratan, David; Belling, Jason; Berche, Bertrand; Botana, Antia; Caram, Justin R; Celardo, Luca; Cuniberti, Gianaurelio; Dianat, Arezoo; Guo, Yuqi; Gutierrez, Rafael; Herrmann, Carmen; Hihath, Josh; Kale, Suneet; Kurian, Philip; Lai, Ying-Cheng; Medina, Ernesto; Mujica, Vladimiro; Naaman, Ron; Noormandipour, Mohammadreza; Palma, Julio; Paltiel, Yossi; Petuskey, William; Ribeiro-Silva, Joao Carlos; Stemer, Dominik; Valdes-Curiel, Ana; Varela, Solmar; Waldeck, David; Weiss, Paul S; Zacharias, Helmut; Wang, Qing Hua | Abstract: The interest in chiral degrees of freedom occurring in matter and in electromagnetic fields is experiencing a renaissance driven by recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials. The CISS effect underpins the fact that charge transport through nanoscopic chiral structures has been conclusively shown to favor a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest unique opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision. Any technology that relies on optimal charge transport -- i.e., the entire quantum device industry -- could benefit from chiral quantum properties. These can be theoretically and experimentally investigated from a quantum information perspective, which is presently lacking. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to affect how well quantum information is stored, transduced and manipulated. This forward-looking review article provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects, and presents a vision for their future role in enabling room-temperature quantum technologies.
7 citations
TL;DR: In this paper, a numerically exact first-principles many-body approach was used to revisit the "prototypical" Kondo case of a cobalt impurity on copper, revealing an unexpectedly strong dependence of the screening properties on the parametrization of the local Coulomb tensor.
Abstract: Using a numerically exact first-principles many-body approach, we revisit the "prototypical" Kondo case of a cobalt impurity on copper. Even though this is considered a well understood example of the Kondo effect, we reveal an unexpectedly strong dependence of the screening properties on the parametrization of the local Coulomb tensor. As a consequence, the Kondo temperature can vary by orders of magnitude depending on the complexity of the parametrization of the electron-electron interaction. Further, we challenge the established picture of a spin-$1$ moment involving two cobalt $d$-orbitals only, as orbital-mixing interaction terms boost the contribution of the remainder of the $d$-shell.
2 citations
TL;DR: In this paper, the authors explore the limits of this approach by comparing computed interatomic transmission pathways with IETS intensities for different molecular junctions, employing a new efficient implementation for evaluating IETS intensity via the mode-tracking algorithm.
Abstract: Inelastic Electron Tunneling Spectroscopy (IETS) is a powerful tool to study the properties of molecular junctions. In particular, it is considered useful for extracting information on electron transport pathways. We explore the limits of this approach by comparing computed interatomic transmission pathways with IETS intensities for different molecular junctions, employing a new efficient implementation for evaluating IETS intensities via the mode-tracking algorithm. We find that while a correlation be- tween pathways and IETS intensities indeed holds when vibrations are clearly localized on atoms off the transport pathway, there is no such correlation for molecules with less localized vibrations, even if transport pathways only sample part of the molecule, and even if a statistical analysis over the vibrational modes is made. This could indicate that the significance of IETS signals for transport pathways is limited to molecules with localized vibrational modes.