Can Electron Transport through a Blue-Copper Azurin Be Coherent? An Ab Initio Study

Theoretical studies of the coherent electronic transport in a system of coupled quantum wires show that switching on the conducting channel in one wire can be manifested in the other coupled wires. Interference processes and electronic correlations are taken into account in our studies on the same footing. The conductance changes depend on the interference conditions of a transmitted wave with that one reflected from the wires that indirectly influence the transport. We show that electronic correlations lead to a dynamical Coulomb blockade effect, which changes the conductance response quantitatively but its shape is still kept the same. Our results are discussed in correspondence with an experiment recently performed by Morimoto et al. [Appl. Phys. Lett. 82, 3952 (2003)] on a system of coupled quantum wires.

Graphene nanoribbons provide an opportunity to integrate phase-coherent transport phenomena with nanoelectromechanical systems (NEMS). Due to the strain induced by a deflection in a graphene nanoribbon resonator, coherent electron transport and mechanical deformations couple. This coupling can be used for sensitive displacement detection in both armchair and zigzag graphene nanoribbon NEMS. Here it is shown that for ordered as well as disordered ribbon systems of length $L$, a strain $\ensuremath{\epsilon}\ensuremath{\sim}{(w/L)}^{2}$ due to a deflection $w$ leads to a relative change in conductance $\ensuremath{\delta}G/G\ensuremath{\sim}({w}^{2}/{a}_{0}L)$, where ${a}_{0}\ensuremath{\approx}1.4$ \AA{}.

The conformation of dimethyl (R,R)-tartrate has been analyzed on the basis of the single crystal X-ray diffraction method as well as by ab-initio quantum chemical studies. The results showed that the extended T conformation containing two planar hydroxyester moieties predominates in both ab-initio and X-ray studies. The lowest energy conformer in ab-initio calculations has C2 symmetry and hydrogen bonds between a hydroxyl group and the nearest carbonyl oxygen. The second in energetical sequence, with an energy difference of only 1.2 kcal/mol, is the asymmetrical conformer, which differs from the lowest energy form by the rotation of one of the ester groups by 180°. Intramolecular OH...O hydrogen bonds observed in this rotamer again involve only proximal functional groups. This conformer is present in the crystal structure of the studied compound, although its conformation in the solid state is no longer stabilized by intramolecular hydrogen bonds of the type mentioned above. In the crystal, hydroxyl groups are mostly involved in intermolecular hydrogen bonds and form only a weak intramolecular hydrogen bond with each other. The planar arrangement of the α-hydroxyester moieties combined with the extended conformation of the carbon chain seems to be stabilized by the intramolecular hydrogen bonds between neighboring functional groups and by the long range dipole-dipole interactions between two pairs of CO and (β)C-H bonds.

In this work, I use the Korringa-Kohn-Rostoker (KKR) method to analyze the possibility of using magnetic tunnel junctions (MTJ) to detect magnetic skyrmions. Usually, These junctions require a magnetic reference layer and then show the well-known Tunneling magnetoresistance effect (TMR). However, under the right conditions, the non-collinear magnetic structure of skyrmions can lead to a significant increase in conductance through a tunnel junction even without a magnetic reference layer. While a large part of the Overall change in conductance can be attributed to the disturbance of quantum well states (QWS) in the iron monolayer hosting the skyrmion, the majority of the effect, including the increase, is due to the scattering of electronic states from the lead at the skyrmion. This is an interesting situation which demonstrates that scattering does not necessarily reduce conductance, but can also increase conductance drastically if coherent transport is blocked by the symmetry of the electronic states in the ferromagnetic case. The combination of vanadium as lead material with a MgO barrier was identified as a material combination where coherent transport in the collinear ferromagnetic base structure is suppressed, but can be enhanced by scattering of electronic states. Beyond that, I show that the presence of a skyrmion in a tunnel barrier not only alters the conductance but also changes the Seebeck coeffcient. It turns out that the absolute value of the Seebeck coeffcient tends to be reduced by the skyrmion. Since antiferromagnetic skyrmions offer several advantages over ferromagnetic skyrmions but are much harder to handle and detect than their ferromagnetic counterparts, I investigate how useful the proposed effect might be for the detection of antiferromagnetic skyrmions. The results indicate that the electronic transport is, in principle, also sensitive to antiferromagnetic non-collinear structures. Finally, I take a brief excursion into the topic of the TMR effect, which requires a magnetic reference layer but can potentially be used to distinguish between different types of non-collinear structures by doing multiple measurements with low spatial resolution.

Recently, multiple quantum wells structure are often used in the laser and diode applications in order to increase their efficiency. In this structure, electron tunnelling phenomena from a quantum well to another well play a key role in electronic transport itself. Tunnelling is a quantum mechanical phenomenon where an electron is commonly represented by its wavefunction. This paper presents a numerical simulation of electron tunnelling probability on three quantum wells (quadruple barrier) Si/SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> system focusing the applied bias effect on the tunnelling probability. The tunneling probability is calculated by solving the Schrodinger's equations through potential barrier using transfer matrix method. The simulation results show the mini-band formation due to the appearance of discrete energy group. We also found that the applied bias on this structure causes the changes in tunnelling probability and discrete energy gap. Therefore, the control of voltage bias and device structure is required in order to obtain expected characteristic of multiple quantum well structure.

Electronic structure and transport study of ligand protected gold magic cluster Au20

Gaussian wavepacket dynamics and quantum tunneling in asymmetric double-well systems

Based on the extended Blonder-Tinkham-Klapwijk (BTK) approach, we have investigated the coherent quantum transport in two-dimensional electron gas/superconductor (2DEG/SC) double tunneling junctions in the presence of the Rashba spin-orbit coupling (RSOC). It is found that all the reflection coefficients in BTK theory as well as conductance spectra oscillate with the external voltage and energy. The oscillation feature of conductance can be tuned largely by the RSOC for low insulating barriers, while for high insulating barriers it is almost independent of the RSOC. These phenomena are essentially different from those found in ferromagnet/superconductor double tunneling junctions.

Recent low-temperature electron transport experiments in high-quality graphene rely on a technique of doped graphene leads, where the coupling between the graphene flake and its metallic contacts is increased by locally tuning graphene to high doping near the contacts. While this technique is widely used and has demonstrated its usefulness numerous times, little is known about the actual transport properties of the doped graphene leads. Here, we present an experiment probing those properties in the quantum Hall regime at low temperature and high magnetic field, showing that electronic phase coherence and transport chirality are preserved, despite the significant charge equilibration occurring at the edges of the leads. Our work yields a finer understanding of the properties of the doped graphene leads, allowing for improvements of the contact quality that can be applied to other two-dimensional materials.

The electrical transport properties of typical hexagonal metals are anisotropic because of their anisotropic lattice structures. Unexpectedly, we show that the electron transport properties in hexagonal close-packed (hcp) noble metals are almost isotropic. Although the electron transport properties of an individual electronic band are highly anisotropic, the total contributions are almost equal in different crystalline orientations because of the complementary contributions of different bands. The electron transport is severely limited by phonons for metals with multisheet Fermi surfaces and optical phonon polarizations. However, it is found the electron-phonon interactions are weak in hcp noble metals, although their Fermi surfaces and phonon spectra are complicated. The electronic structure acts as a phonon filter, resulting in small electron-phonon scattering rates. The weak electron-phonon interactions are beneficial to electron and thermal transport, indicating hcp noble metals have great potential to be used in electronics and solar cells.

A cyclometalated complex of Ir(III) is covalently tethered to DNA oligonucleotides and serves as both a photooxidant and photoreductant in the study of DNA-mediated hole transport (HT) and electron transport (ET). Spectroscopic and melting temperature studies support intercalation of the tethered complex into the DNA duplex through the functionalized dppz ligand. Using these tethered assemblies, ET and HT is initiated in DNA by the same photoredox probe. Cyclopropylamine substituted bases, N4-cyclopropylcytosine (CPC) and N2-cyclopropylguanine (CPG) are used as kinetically fast electron and hole traps to probe the resulting electron migration processes after direct irradiation of the tethered Ir assembly. Oxidation of CPG and CPC is promoted efficiently by HT from photoexcited Ir(III) when the modified bases are positioned in the purine strands of the A-tract. In contrast, when CPC is embedded in a pyrimidine tract, ET to yield reductive decomposition is observed. Thus, the Ir(III)-tethered DNA assembly containing cyclopropyl-modified bases provides a unique model system to explore the two DNA-mediated electron migration processes using the same photoredox probe and the same DNA bridge.

The tunneling probability for majority carriers in an ohmic contact to n-type GaAs has been calculated by directly solving the Schrödinger equation for the wave functions in the semiconductor depletion region. The direct solution is straightforward and relies on fewer assumptions than previous calculations based on the WKB approximation. It also provides a useful application of undergraduate quantum mechanics to an important area of VLSI semiconductor technology. The direct solution can be performed on an 80286 machine in less than a minute and yields tunneling probabilities roughly twice as large as the WKB approximation at most electron energies. The tunneling probability is then used to calculate the contact resistance as a function of doping for the contact. The contact resistances are approximately one-half the resistances calculated using the WKB method.

Effects of electron-phonon intervalley scattering and band non-parabolicity on electron transport properties of high-temperature phase SnSe: An ab initio study

The solid electrolyte interphase (SEI) is a solid that forms between the anode and electrolyte in batteries. It is made up electrolyte species that have decomposed due to reduction by the anode, but its growth is self-limited as its very presence inhibits further electrolyte decomposition. The SEI is made up of numerous inorganic and organic species, and its composition and properties can vary drastically. For the proper operation of the battery, it needs to be ionically conducting while being electronically insulating. These two properties are often correlated, so it is important to understand how to decouple them to achieve desired battery performance.In this presentation, we will discuss results from our group on studying electron transport through simplified models of the SEI from first-principles atomistic modeling. Our approach uses the non-equilibrium Green's function technique in combination with density functional theory (NEGF-DFT) to calculate electron transport through SEI structures. We first applied this method to compare the electronic conductivity of single-crystal versus polycrystalline LiF, a common inorganic SEI component. The grain boundaries in polycrystalline LiF are known to be essential for Li ion transport, but they also make for leakage pathways for electrons to pass through the material. Next, we apply the same method to investigate the SEI in Ca ion batteries, with a study of electron transport through CaF2. In this study, we considered single-crystal CaF2, as well as several grain boundaries and an amorphous version of CaF2. We found the amorphous version of this SEI component to be orders of magnitude more electronically conductive than the crystalline counterparts.Finally, we used ab initio molecular dynamics (AIMD) to contrast the reductive decomposition of two electrolyte solvents: tetrahydrofuran (THF) and ethylene carbonate (EC) at a Ca anode. The former does not decompose in the timescales of our simulations (ca. 50 ps), while the latter undergoes rapid decomposition. We extracted structural atomistic snapshots from our AIMD trajectories and fed them through the NEGF-DFT code to obtain time-dependent electron transport for the THF and EC solvents near the Ca anode, while decompositions are occurring in the EC system. While THF is more conductive than EC, its conductivity has relatively small variation in time. EC has drastic fluctuations in its conductivity, part of which can be attributed to individual molecular decomposition events, which may be useful to develop diagnostic or characterization techniques.The SEI plays an essential role in maintaining long-term battery stability. Understanding how electron transport occurs through this battery component will help develop SEIs with desired properties for ultimate performance in both Li-ion batteries and beyond Li-ion batteries such as Ca ion and other multivalent systems.

Coherent transport phenomena are difficult to observe due to several sources of decoherence. For instance, in the electronic transport through quantum devices the thermal smearing and dephasing, the latter induced by inelastic scattering by phonons or impurities, destroy phase coherence. In other wave systems, the temperature and dephasing may not destroy the coherence and can then be used to observe the underlying wave behaviour of the coherent phenomena. Here, we observe coherent transmission of mechanical waves through a two-dimensional elastic Sinai billiard with two waveguides. The flexural-wave transmission, performed by non-contact means, shows the quantization when a new mode becomes open. These measurements agree with the theoretical predictions of the simplest model highlighting the universal character of the transmission fluctuations.