Remodeling Zinc Deposition via Multisite Zincophilic Chlorophyll for Powerful Aprotic Zinc Batteries.

The organic electrolyte can resolve the hurdle of hydrogen evolution in aqueous electrolytes but suffers from sluggish electrochemical reaction kinetics due to a compromised mass transfer process. Herein, we introduce a chlorophyll, zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (Chl), as a multifunctional electrolyte additive for aprotic zinc batteries to address the related dynamic problems in organic electrolyte systems. The Chl exhibits multisite zincophilicity, which significantly reduces the nucleation potential, increases the nucleation sites, and induces uniform nucleation of Zn metal with a nucleation overpotential close to zero. Furthermore, the lower LUMO of Chl contributes to a Zn-N-bond-containing SEI layer and inhibits the decomposition of the electrolyte. Therefore, the electrolyte enables repeated zinc stripping/plating up to 2000 h (2 Ah cm-2 cumulative capacity) with an overpotential of only 32 mV and a high Coulomb efficiency of 99.4%. This work is expected to enlighten the practical application of organic electrolyte systems.

Tunable surface magnetism by gate voltage in a slab of nonmagnetic half-Heusler compound CoTiSb.

The electrical manipulation of magnetization is appealing to the relevant experiment and spintronic device. In this paper, we focus on the electrical and magnetic properties of a thin film cleaved from the nonmagnetic half-Heusler compound CoTiSb. By means of the first-principles calculations, we find that the surface of TiSb termination possesses ferrimagnetism with a magnetic moment of 0.35 (0.49) µB per unit cell without (with) Hubbard U, which can persist below the Curie temperature of 48 (54) K. What is more, such a surface magnetism can be tuned to nonmagnetism by gate-induced hole doping with a concentration of 2.83 × 1014 (3.55 × 1014) cm-2. This magnetic tunability of the CoTiSb slab provides a platform to realize the pseudo-spin valve with both the magnetic electrodes and nonmagnetic space layer made of the same material without hetero-interfaces.

The nearly free electron states and the conductivity limited by electron-phonon scattering of an OH-terminated MXene material, a case study of the Hf2C(OH)2 monolayer.

Reducing the electron-phonon scattering is always desirable for realizing high conductivity of actual materials at room temperature. It is seemingly feasible in some OH-terminated MXenes such as the Hf2C(OH)2 monolayer, which hosts the so-called nearly free electron states (NFESs) near the Fermi energy. The NFESs are characterized by a large separation between the major electronic probability distribution and the atomic layer of MXenes. This implies that the NFESs suffer from a very weak electron-phonon scattering, hence the high conductivity at room temperature of these materials. We perform first principles calculations on the conductivity limited by the electron-phonon (e-ph) scattering of the Hf2C(OH)2 monolayer. Our results indicate that the conductivity of the Hf2C(OH)2 monolayer at room temperature is indeed higher than those of most of the MXene materials. However, such a high conductivity cannot be attributed to the existence of the NFESs because of their relatively low electronic band velocity. This conclusion is applicable to other OH-terminated MXene materials such as Zr2C(OH)2 since their band structures around the Fermi energy are highly analogous. Our study suggests that both large band velocity and weak e-ph coupling are important for realizing ultrahigh conductivity facilitated by the NFESs in materials.

An Autonomous Path Planning Model for Unmanned Ships Based on Deep Reinforcement Learning.

Deep reinforcement learning (DRL) has excellent performance in continuous control problems and it is widely used in path planning and other fields. An autonomous path planning model based on DRL is proposed to realize the intelligent path planning of unmanned ships in the unknown environment. The model utilizes the deep deterministic policy gradient (DDPG) algorithm, through the continuous interaction with the environment and the use of historical experience data; the agent learns the optimal action strategy in a simulation environment. The navigation rules and the ship's encounter situation are transformed into a navigation restricted area, so as to achieve the purpose of planned path safety in order to ensure the validity and accuracy of the model. Ship data provided by ship automatic identification system (AIS) are used to train this path planning model. Subsequently, the improved DRL is obtained by combining DDPG with the artificial potential field. Finally, the path planning model is integrated into the electronic chart platform for experiments. Through the establishment of comparative experiments, the results show that the improved model can achieve autonomous path planning, and it has good convergence speed and stability.

Electron-phonon scattering limited hole mobility at room temperature in a MoS2 monolayer: first-principles calculations.

Based on first-principles calculations and iterative solution of the Boltzmann transport equation, we theoretically study the room temperature mobility (RTM) of a valence band hole in a MoS2 monolayer (ML) limited by electron-phonon (e-ph) scattering. The hole mobility obtained by us is 26.0 cm2 V-1 s-1 at 300 K. This is a value much closer to the experimental result (about 40.0 cm2 V-1 s-1). In contrast, the semi-empirical estimate based on the deformational potential (DP) model in previous literature gave a value of 200.5 cm2 V-1 s-1, far away from the experimental data. By a detailed analysis, we find that unlike the case of conduction band electrons, the intervalley scattering realized by longitudinal acoustic (LA) phonons plays a dominant role in influencing the hole mobility. And this is the main reason for the DP model failing to give a quantitative estimate of the hole RTM in MoS2-ML.

Rational designing of 8-hydroxyquinolin-imidazolinone-based fluorescent protein mutants with dramatically red shifted emission: A computational study.

Engineering fluorescent proteins to be the customized in vivo labels for monitoring cellular dynamic events is critical in biochemical and biomedical studies. The design and development of novel red fluorescent proteins is one of the most important fronts in this field due to their potential of imaging the entire organism. A recent fluorescent protein mutant eqFP650-67-HqAla with the 8-hydroxyquinolin-imidazolinone (HQI) chromophore has the plausible bathochromic shift of ~30 nm in its emission spectrum wavelength comparing to the parent fluorescent protein eqFP650. However, molecular mechanism of this significant shift remains somewhat obscure. In this study, we carefully benchmarked our computational methods and performed extensive calculations to investigate various structural components' effect on the chromophore's emission energy and decipher the molecular origin of the spectral shift. The influences of conjugation size, substituent group, substituent site as well as the number of substituents have been examined by elaborately designed chromophore derivatives. Accordingly, we proposed several chromophore mutants with dramatic bathochromic shift of up to ~60 nm in their emission spectra. We further evaluated their structural stability in the protein using molecular dynamics simulations. Present theoretical study connects the structural feature of chromophore derivatives in red fluorescent proteins with their splendid performances in shifting the emission frequency and offer the molecular insight. The computational protocol and successive examination procedure to extract the structural effect utilized herein can also be widely applied to other fluorescent proteins in general. © 2018 Wiley Periodicals, Inc.

Influence of Lifshitz Transition on the Intrinsic Resistivity of Cu2N Monolayer.

The Lifshitz transition (LT), a topological structure transition of Fermi surfaces, can induce various intricate physical properties in metallic materials. In this study, through first-principles calculations, we explore the nontrivial effect of the LT on the intrinsic resistivity of the Cu2N monolayer arising from electron-phonon (el-ph) scattering. We find that when the LT is induced by electron doping, the multibranch Fermi surface simplifies into a single-band profile. Such an LT leads to a decoupling of low-frequency flexural phonons from el-ph scattering due to mirror symmetry. Consequently, the resistivity of the Cu2N monolayer at room temperature significantly decreases, approaching that of slightly doped graphene, and highlighting the Cu2N monolayer as a highly conductive two-dimensional metal. Moreover, this LT can bring about a nonlinear temperature dependence of the intrinsic resistivity at a high temperature.

Spin filters based on two-dimensional materials Co2Si and Cu2Si.

Spintronic devices have several advantages compared with conventional electronic devices, including non-volatility, faster data processing speed, higher integration densities, less electric power consumption and so on. However, we still face challenges for efficiently generating and injecting pure spin polarized current. In this work, we utilize two kinds of two-dimensional materials Co2Si and Cu2Si with both lattice match and band match to construct devices and then research their spin filter efficiency. The spin filter efficiency can be improved effectively either by an appropriate gate voltage at Co2Si region, or by series connection. In both cases the filter efficiencies are much larger than two-dimensional prepared Fe3GeTe2spin valve and ferromagnetic metallic chairlike O-graphene-H. Also at a quite small bias, we obtain a comparable spin polarized current as those obtained in Fe3GeTe2spin valve and O-graphene-H obtained at a much larger bias. .

Giant magnetoresistance in spin valves realized by substitutingY-site atoms in Heusler lattice.

'All-Heusler' spin-valve constructed by two half-metallic Heusler electrodes and a non-magnetic Heusler spacer contains two interfaces that have a crucial influence on the magnetoresistance. In order to reduce the disorder at the interface and protect the half metallicity of the electrode at the same region, we propose a scheme to construct a spin valve by replacing theY-site atoms in the half-metallic Heusler electrode to obtain the corresponding non-magnetic spacer based on the Slater-Pauling rule. In this way, the lattice and band match of the two materials can be ensured naturally. By using Co2FeAl as electrode and Co2ScAl as the spacer materials, we construct the Co2FeAl/Co2ScAl/Co2FeAl(001)-spin valve. Based on the first-principles calculation, the most stable FeAl/CoCo-interface is determined both from the phonon spectra and the formation energy when the spacer Co2ScAl grows on the FeAl-terminated (001) surface of electrode material Co2FeAl. By comparing the projected density of states of the interfacial atoms with the corresponding density of states of the bulk electrode material, only the value of spin-up state of Al changes from 0.17 states/atom/eV to 0.06 states/atom/eV before and after substitution, the half metallicity at the interface is maintained. As a result, the spin-dependent transport properties show significant theoretical magnetoresistance MRopwhich can reach up to 1010% and much larger than 106% reported before.

Magneto-transport properties of gapped graphene.

Based on the Kubo formula, we have studied the electron transport properties of a gapped graphene in the presence of a strong magnetic field. By solving the Dirac equation, we find that the Landau level spectra in two valleys differ from each other in that the n = 0 level in the K valley is located at top of the valence band, whereas it is at the bottom of the conduction band in the K' valley. Thus, in an individual valley, the symmetry between conduction and valence bands is broken by the presence of a magnetic field. By using the self-consistent Born approximation to treat the long range potential scattering, we formulate the diagonal and the Hall conductivities in terms of the Green function. To perform the numerical calculation, we find that a large bandgap can suppress the quantum Hall effect, owing to the enhancement of the bandgap squeezing the spacing between the low-lying Landau levels. On the other hand, if the bandgap is not very large, the odd integer quantum Hall effect experimentally, observed in the gapless graphene, remains in the gapped one. However, such a result does not indicate the half integer quantum Hall effect in an individual valley of the gapped graphene. This is because the heights of the Hall plateaux in either valley can be continuously tuned by the variation of the bandgap. More interestingly, we find that the height of the diagonal conductivity peak corresponding to the n = 0 Landau level is independent of the bandgap if the scattering is not very strong. In the weak scattering limit, we demonstrate analytically that such a peak takes a universal value e(2)/(hpi), regardless of the bandgap.

Magneto-conductivity of Weyl semimetals: the roles of inter-valley scattering and high-order Feynman diagrams.

Within the theoretical framework of Kubo formula and self-consistent Born approximation, we theoretically study the transversal and longitudinal magneto-conductivity of a type-I Weyl semimetal. We focus mainly on the peculiar role of inter-valley scattering on linear transversal magnetoresistance (LTMR) and negative longitudinal magnetoresistance (NLMR). At first, we find that the contributions of high-order Feynman diagrams to the transversal magneto-conductivity play the distinct roles between the cases of intra- and inter-valley scatterings. The former suppresses the transversal conductivity whereas the latter enhances it. Then, with the increase of scattering strength, the LTMR is destroyed, accompanying a sizable increase of transversal conductivity, in particular, in the case of the tilted cone. For longitudinal magneto-transport, inter-valley scattering contributes only trivial magnetoresistance. In contrast, intra-valley scattering is invalid for longitudinal magneto-transport which means a very large NLMR. In addition, the high-order Feynman diagrams always play the nontrivial role on the longitudinal conductivity even in the weak scattering limit. Finally, when altering the Fermi energy among low-lying Landau level, the peaks of transversal conductivity just correspond to the valleys of the longitudinal conductivity.

Effects of uniaxial tensile strain on the electron-phonon scattering limited carrier mobility in an n-type monolayer MoS2 at room temperature: first-principles calculations.

In the present work, we theoretically study the strain effect on the room temperature mobility (RTM) of a n-type Monolayer MoS2 limited by electron-phonon (e-ph) scattering. Our numerical results indicate that the RTM along zigzag direction of such a 2D material can be efficiently modulated by a uniaxial tensile strain. Such an RTM, denoted as [Formula: see text], has a sizable reduction (enhancement) as a moderate tensile strain is applied in a parallel (perpendicular) direction. For example, when the strain strength amounts to 7%, [Formula: see text] the two distinct cases of the strain applied in x and y  directions differ from each other by roughly two times. In contrast, the RTM in armchair direction is not so sensitive to a tensile strain. The underlying mechanism for such a strain effect on the mobility is then analysed in depth. Our results are obtained completely on the level of first-principles calculations, free from any empirical simplifications. Therefore, our above findings provide reliable and detailed information for experimentally manipulating the RTM of a n-type monolayer MoS2 by simply stretching the sample.

Electronic transport property in Weyl semimetal with local Weyl cone tilt.

In realistic materials of Weyl semimetal (WSM), the Weyl cone tilt (WCT) is allowed due to the absence of Lorentz invariance in condensed matter physics. In this context, we theoretically study the electronic transport property in WSM with the local WCT as the scattering mechanism. In so doing, we establish an electronic transport structure of WSM with the WCT occurring only in the central region sandwiched between two pieces of semi-infinite WSM without the WCT. By means of two complementary theoretical approaches, i.e. the continuum-model method and the lattice-model method, the electronic transmission probability, the conductivity and the Fano factor as functions of the incident electron energy are calculated respectively. We find that the WCT can give rise to nontrivial intervalley scattering, as a result, the Klein tunneling is notably suppressed. More importantly, the minimal conductivity of a WSM shifts in energy from the Weyl nodal point. The Fano factor of the shot noise deviates obviously from the sub-Poissonian value in a two dimensional WSM with the WCT.

Magnetic field induced metal-insulator transition in single nodal ring topological semimetals.

Our theoretical investigation indicates that an applied magnetic field can open a gap between the conduction and valence bands of a nodal line semimetal (NLSM), though it is a kind of gapless material in the absence of a magnetic field. The emerging bandgap depends sensitively on the strength and orientation of the magnetic field which implies a tunable and large anisotropy of magnetoresistance in such kinds of topological materials. Following such a theoretical finding, we predict that in some candidates of NSLMs with a single nodal ring, such as the materials of CaP3 family, a transition between metallic and insulating states driven by a magnetic field is possibly observed experimentally. Consequently, a magnetic field can be viewed as a novel mechanism for metal-insulator transition of solid materials, in additional to the well-known conventional ones such as the Anderson and Mott transitions.

Simulation on the electronic wave packet cyclotron motion in a Weyl semimetal slab.

We perform a numerical simulation on the time evolution of an electronic wave packet in a Weyl semimetal (WSM) slab driven by a magnetic field. We find that the evolution trajectory of the wave packet depends sensitively on its initial spin state. Only with initial spin state identical to that of the Fermi arc state at the surface it localized, does the wave packet evolution demonstrate the characteristic cyclotron orbit of WSM previously predicted from a semiclassical viewpoint. By analyzing the eigen-expansion of the electronic wave packet, we find the chiral Landau levels (LLs) of the WSM slab, as ingredients of the wave packet, to be responsible for establishing the characteristic WSM cyclotron orbit. In contrast, the nonchiral LLs contribute irregular oscillations to the wave packet evolution, going against the formation of a well-defined cyclotron orbit. In addition, the tilted magnetic field does not affect the motion of the electronic wave packet along the Fermi arcs in the momentum space. It does, however, alter the evolution trajectory of the electronic wave packet in real space and spin space. Finally, the energy disalignment of the Weyl nodes results in a 3D cyclotron orbit in real space.

Conductivity tensor of graphene dominated by spin-orbit coupling scatterers: A comparison between the results from Kubo and Boltzmann transport theories.

The diagonal and Hall conductivities of graphene arising from the spin-orbit coupling impurity scattering are theoretically studied. Based on the continuous model, i.e. the massless Dirac equation, we derive analytical expressions of the conductivity tensor from both the Kubo and Boltzmann transport theories. By performing numerical calculations, we find that the Kubo quantum transport result of the diagonal conductivity within the self-consistent Born approximation exhibits an insulating gap around the Dirac point. And in this gap a well-defined quantized spin Hall plateau occurs. This indicates the realization of the quantum spin Hall state of graphene driven by the spin-orbit coupling impurities. In contrast, the semi-classical Boltzmann theory fails to predict such a topological insulating phase. The Boltzmann diagonal conductivity is nonzero even in the insulating gap, in which the Boltzmann spin Hall conductivity does not exhibit any quantized plateau.

Band structure of a three-dimensional topological insulator quantum wire in the presence of a magnetic field.

By means of a numerical diagonalization approach, we calculate the electronic structure of a three-dimensional topological insulator (3DTI) quantum wire (QW) in the presence of a magnetic field. The QW can be viewed as a 3DTI film with lateral surfaces, when its rectangular cross section has a large aspect ratio. Our calculation indicates that nonchiral edge states emerge because of the confined states at the lateral surfaces. These states completely cover the valence band region among the Landau levels, which reasonably account for the absence of the [Formula: see text] quantum Hall effect in the relevant experimental works. In an ultrathin 3DTI film, inversion between the electron-type and hole-type bands occurs, which leads to the so-called pseudo-spin Hall effect. In a 3DTI QW with a square cross section, a tilting magnetic field can establish well-defined Landau levels in all four surfaces. In such a case, the quantum Hall edge states are localized at the square corners, characterized by the linearly crossing one-dimensional band profile. And they can be shifted between the adjacent corners by simply rotating the magnetic field.

Armchair-edged nanoribbon as a bottleneck to electronic total transmission through a topologically nontrivial graphene nanojunction.

It is currently a promising approach to experimentally realize the topological insulator phase transition of graphene by introducing the extrinsic spin-orbit coupling (SOC). Then, electronic total transmission through various topological nontrivial graphene nanojunctions (GNJs) is obtainable, if the electronic transport is supported by the helical edge states. Though the bulk graphene is a gapless semiconductor, the inter-valley scattering could introduce a topological trivial gap in semiconducting armchair-edged graphene nanoribbon (GNR). The SOC should be strong enough to reopen a topological nontrivial gap before close such a trivial gap. Therefore, our theoretical study indicates that a semiconducting armchair-edged graphene nanoribbon (GNR) can not develop the helical edge states when the SOC strength is lower than a threshold, though the bulk phase is topological nontrivial. This implies a competition between the SOC and the inter-valley scattering. However, for a metallic armchair-edged GNR, a small SOC can always open a nontrivial gap. Nevertheless, the helical edge state is much less localized than that in a zigzag-edged GNR of the same width. As a result, and by numerically calculating the electronic transmission spectrum of step- and L-shaped GNJs, we conclude that when an armchair-edged GNR is a part of a GNJ, it is the weak point to realize the electronic total transmission even though the bulk phase of graphene is topologically insulating.

Two-dimensional Kagome phosphorus and its edge magnetism: a density functional theory study.

By means of density functional theory calculations, we predict a new two-dimensional phosphorus allotrope with the Kagome-like lattice(Kagome-P). It is an indirect gap semiconductor with a band gap of 1.64 eV. The gap decreases sensitively with the compressive strain. In particular, shrinking the lattice beyond 13% can drive it into metallic state. In addition, both the AA and AB stacked Kagome-P multi-layer structures exhibit a bandgap much smaller than 1.64 eV. Edges in the Kagome-P monolayer probably suffer from the edge reconstruction. An isolated zigzag edge can induce antiferromagnetic (AF) ordering with a magnetic transition temperature of 23 K. More importantly, when applying a stretching strain beyond 4%, such an edge turns to possess a ferromagnetic ground state. A very narrow zigzag-edged Kagome-P ribbon displays the spin moment distribution similar to the zigzag-edged graphene nanoribbon because of the coupling between the opposites edges. But the inter-edge coupling in the Kagome-P ribbon vanishes more rapidly as the ribbon width increases. These properties make it a promising material in spintronics.

RKKY interaction in graphene with a line defect.

A kind of extended line defect is currently an experimentally available one-dimensional topological structure in graphene lattice. It modifies the electronic properties of graphene in many aspects. For example, it induces an even-parity boundary state which has linear dispersion and breaks the electron-hole symmetry of the graphene electronic structure. In addition, the line defect possesses much stronger adsorption ability to the metal adatoms than the ordinary graphene lattice point. In the present work, by developing an analytical lattice Green's function technique, we theoretically study the RKKY interaction in graphene when two magnetic impurities are adsorbed near the line defect. We find that R(-3) decay rate of the RKKY interaction unique to graphene still holds true in the presence of the line defect. But another feature of the RKKY interaction in graphene, referred to as the Saremi's rule, which claims the RKKY interactions between the same or opposite sublattice points are ferro- or antiferromagnetic respectively, is no longer preserved due to the influence of the boundary state around the line defect. More importantly, the RKKY interaction on the line defect is greater than its counterpart in the pristine graphene by about one or two orders of magnitude. The local lattice distortion around the line defect can bring about the transition of the RKKY interaction between ferro- and antiferromagnetic orders. Such a result implies that the presence of the extended line defect provides a feasible platform in graphene to realize the long-range magnetic order even at a high temperature.