Coulomb Repulsion Research Articles

Intermolecular interactions in clusters of ethylammonium nitrate and 1-amino-1,2,3-triazole.

The intermolecular interaction energies, including hydrogen bonds (H-bonds), of clusters of the ionic liquid ethylammonium nitrate (EAN) and 1-amino-1,2,3-triazole (1-AT) based deep eutectic propellants (DeEP) are examined. 1-AT is introduced as a neutral hydrogen bond donor (HBD) to EAN in order to form a eutectic mixture. The effective fragment potential (EFP) is used to examine the bonding interactions in the DeEP clusters. The resolution of the Identity (RI) approximated second order Møller-Plesset perturbation theory (RI-MP2) and coupled cluster theory (RI-CCSD(T)) are used to validate the EFP results. The EFP method predicts that there are significant polarization and charge transfer effects in the EAN:1-AT complexes, along with Coulombic, dispersion and exchange repulsion interactions. The EFP interaction energies are in good agreement with the RI-MP2 and RI-CCSD(T) results. The quasi-atomic orbital (QUAO) bonding and kinetic bond order (KBO) analyses are additionally used to develop a conceptual and semi-quantitative understanding of the H-bonding interactions as a function of the size of the system. The QUAO and KBO analyses suggest that the H-bonds in the examined clusters follow the characteristic hydrogen bonding three-center four electron interactions. The strongest H-bonding interactions between the (EAN)1:(1-AT)n and (EAN)2:(1-AT)n (n = 1-5) complexes are observed internally within EAN; that is, between the ethylammonium cation [EA]+ and the nitrate anion ([NO3]-). The weakest H-bonding interactions occur between [NO3]- and 1-AT. Consequently, the average strengths of the H-bonds within a given (EAN)x:(1-AT)n complex decrease as more 1-AT molecules are introduced into the EAN monomer and EAN dimer. The QUAO bonding analysis suggests that 1-AT in (EAN)x:(1-AT)n can act as both a HBD and a hydrogen bond acceptor simultaneously. It is observed that two 1-AT molecules can form H-bonds to each other. Although the KBOs that correspond to H-bonding interactions in [EA]+:1-AT, [NO3]-:1-AT and between two 1-AT molecules are weaker than the H-bonds in EAN, those weak H-bond networks with 1-AT could be important to form a stable DeEP.

Nuclear Astrophysics at the Low-Energy Frontiers: Updates from underground laboratories

Nuclear fusion reactions are the heart of nuclear astrophysics: they sensitively influence the nucleosynthesis of the elements in the earliest stages of the Universe and in all the objects formed thereafter; control the associated energy generation and neutrino luminosity; influence the evolution of stars. Unfortunately, measuring reaction cross sections at astrophysically relevant energies is exceptionally challenging due to Coulomb repulsion between nuclei, resulting in cross section values as low as fbar. Laboratorial measurements of these cross sections are often unfeasible due to overwhelming cosmic-ray-induced backgrounds. One effective solution to this problem is to conduct experiments in underground laboratories. The Laboratory for Underground Nuclear Astrophysics (LUNA) is an experimental approach based on an underground accelerator focusing on studying nuclear fusion reactions. Its primary objective is to accomplish direct measurement of cross sections for nuclear reactions that have significance in stellar and primordial nucleosynthesis. This article will present the latest findings and future objectives.

Unprecedented energy storage in metal-organic complexes via constitutional isomerism.

The essence of any electrochemical system is engraved in its electrical double layer (EDL), and we report its unprecedented reorganization by the structural isomerism of molecules, with a direct consequence on their energy storage capability. Electrochemical and spectroscopic analyses in combination with computational and modelling studies demonstrate that an attractive field-effect due to the molecule's structural-isomerism, in contrast to a repulsive field-effect, spatially screens the ion-ion coulombic repulsions in the EDL and reconfigures the local density of anions. In a laboratory-level prototype supercapacitor, those with β-structural isomerism exhibit nearly 6-times elevated energy storage compared to the state-of-the-art electrodes, by delivering ∼535 F g-1 at 1 A g-1 while maintaining high performance metrics even at a rate as high as 50 A g-1. The elucidation of the decisive role of structural isomerism in reconfiguring the electrified interface represents a major step forward in understanding the electrodics of molecular platforms.

A theoretical study on pseudo Mott phase transition of vanadium dioxide.

The structural phase transition (SPT) and metal-insulator phase transition (MIT) always occur simultaneously upon heating from the low-temperature insulator M1 phase to the high-temperature metal R phase in vanadium dioxide, and it is still unclear which one of Mott correlation and Peierls distortion plays a decisive role in the thermally induced phase transition (PT) since 1959. Our density functional theory (DFT)-based calculations revealed that the intermediate phase in the PT, the so-called monoclinic metal phase, is a zero indirect band gap semimetal (P21/c space group) with a pseudo gap (199 meV). From the M1 phase to the monoclinic metal phase, the band gap decreases gradually to zero, and the bonding lengths between vanadium-vanadium atoms remain nearly constant. The SPT and MIT from the intermediate structure to the R phase occur simultaneously with a sudden change of bonding lengths between vanadium-vanadium atoms, in which electrons can jump down rather than jump up to the conduction band minimum (CBM) from the valence band maximum (VBM) under thermal fluctuation in order to lower the total energy of the system to push forward the occurrence of PT. The electron jumping does not require additional energy from Coulomb repulsion between electrons even though it is always present. This SPT is a typical Peierls PT or a pseudo Mott PT rather than an actual Mott PT in the each of the two stages. Our conclusions provide a new understanding of SPT and MIT in vanadium dioxide that has been debated for more than 80 years.

О дираковской массе хаббардовских фермионов в сильно коррелированном топологическом сверхпроводнике высокого порядка

Majorana corner modes have a number of advantages over the classical Majorana states in terms of performing topologically protected quantum computations. However, the problem of the influence of Coulomb repulsion on higher-order phases, which inevitably arises when trying to implement such systems in practice, has been poorly studied. In this article, we analyze the features of a topological invariant describing the nontrivial phase with the corner modes for a two-dimensional two-orbital model of a hybrid structure in the regime of extremely strong electron correlations. For this purpose, approximate wave functions of the edge states with a linear dispersion law and the associated Dirac masses, which arise when superconducting pairing in the system is taken into account, are obtained.

Atomization and combustion characteristics of a biodiesel–ethanol fuel droplet in a uniform DC electric field

Electric field has the potential to influence the combustion characteristics of hydrocarbon fuel. In this paper, the atomization and combustion characteristics of the droplets of biodiesel and biodiesel–ethanol blend in a uniform direct-current electric field were investigated using photography. It was revealed that a certain electric field strength could induce droplet deformations and cone jets. For the droplet blended with 10 vol. % ethanol, the sizes of the secondary droplets from bubble breakups decreased with the increase in electric field strength, possibly due to the Coulomb repulsion in the ligament. The high breakup intensity of the droplet blended with 30 vol. % and 50 vol. % ethanol covered up the effect of electric field on the sizes of secondary droplets from bubble breakups. During the entire range of electric field strength, cone jets generated smaller secondary droplets in comparison with bubble breakups. Moreover, the electric field distorted the flame morphology, especially the flame width increased at the electric field strength of 50 kV/m. The maximum droplet temperature decreased with the electric field strength, in addition to the biodiesel droplet. Overall, the electric field ameliorates fuel droplets' atomization and combustion characteristics.

Keplerian orbits and global asymptotic solution in the form of an Airy function for the scattering problem on a repulsive Coulomb potential

Keplerian orbits and global asymptotic solution in the form of an Airy function for the scattering problem on a repulsive Coulomb potential

Exciton insulator in a moiré lattice

Interlayer electron and hole can be paired up through coulomb interaction to form an exciton insulator when their kinetic energy is substantially smaller than the interaction energy. The traditional platform to realize such an interlayer interaction is the double quantum well with dielectric material between electron and hole, for which an external magnetic field is required to generate Landau level flat bands that can reduce the kinetic energy of charged carriers. When both quantum wells are at the half filling of the lowest landau level, the electron-electron repulsive interaction, by the particle-hole transformation in one well, will be equivalent to electron-hole attractive interaction, from which interlayer exciton and its condensation can emerge. In a two-dimensional twisted homostructure or an angle aligned heterostructure, there exists a moiré superlattice, in which bands are folded into the mini-Brillouin zone by the large moiré period. Gap opening at the boundary of mini-Brillouin zone can form the well-known moiré flat band. This review will discuss how to use the moiré flat bands to generate exciton insulator in the absence of external magnetic field in transitional metal dichalcogenide (TMD) moiré heterostructure. Unlike the double quantum well where symmetric well geometry is used, the moiré related sample can have multiple different geometries, including monolayer TMD-hexagonal boron nitride-moiré structure, moiré-moiré structure, and monolayer TMD-bilayer TMD structure. The carriers in those structures can be well tuned to locate equally in different layers, and particle-hole transformation in the moiré first Hubbard band can transform the interlayer repulsive coulomb interaction into attractive interaction, which is the same as that in quantum well under magnetic field. We will show that by using differential contrast reflection spectrum, interlayer photoluminescence, 2s exciton sensing, quantum capacitance and microwave impedance microscopy, the signature of exciton fluid can be identified. The excitonic coherence features in those structures will promise by using the coulomb drag technique and counter flow technique in future. In general, exciton in moiré lattice is a promising candidate for studying the Bose-Hubbard model in solids and can well realize exciton superfluidity, excitonic mott insulator as well as the crossover between them.

Perspectives on determinism in quantum mechanics: Born, Bohm, and the "Quantal Newtonian" laws.

Quantum mechanics has a deterministic Schrödinger equation for the wave function. The Göttingen-Copenhagen statistical interpretation is based on the Born Rule that interprets the wave function as a "probability amplitude." A precept of this interpretation is the lack of determinism in quantum mechanics. The Bohm interpretation is that the wave function is a source of a field experienced by the electrons, thereby attributing determinism to quantum theory. In this paper, we present a new perspective on such determinism. The ideas are based on the equations of motion or "Quantal Newtonian" Laws obeyed by each electron. These Laws, derived from the temporal and stationary-state Schrödinger equation, are interpreted in terms of "classical" fields whose sources are quantal expectations of Hermitian operators taken with respect to the wave function. According to the Second Law, each electron experiences an external field-the quantal Coulomb-Lorentz law. It also experiences an internal field representative of properties of the system: correlations due to Coulomb repulsion and Pauli principle; the density; kinetic effects; and an internal magnetic field component. There is a response field. The First Law states that the sum of the external and internal fields experienced by each electron vanishes. These fields are akin to those of classical physics: They pervade all space; their structure is descriptive of the quantum system; the energy of the system is stored in these fields. It is in the classical behavior of these fields, which arise from quantal sources that one may then speak of determinism in quantum mechanics.

Molecular dynamics study of ionic diffusion and the FLiNaK salt melt structure

In the present work, we carried out a molecular dynamics study of the kinetic properties of the FLiNaK molten salt, as well as a detailed study of the structure of this salt melt. The high value of the self-diffusion coefficient of fluorine ions is due to the large number of Coulomb repulsions between the most numerous negative ions. The calculated values of shear viscosity are in good agreement with the experimental data, as well as with the reference data obtained on the basis of finding the most reliable data. The total and partial functions of the radial distribution are calculated. According to the statistical analysis, fluorine ions have the greatest numerical diversity in the environment of similar ions, and sodium ions with the lowest representation in FLiNaK, have the least such diversity. For the subsystem of fluorine ions, the rotational symmetry of the fifth order is the most pronounced. Some of the fluorine ions form linear chains consisting of three atoms, which are not formed for positive ions. The results of the work give an understanding of the behavior molten FLiNaK under operating conditions in a molten salt reactor and will find application in future studies of this molten salt.

Proton emission from halo nuclei induced by intense x-ray lasers

We investigate the proton emission from halo nuclei induced by intense x-ray lasers within the framework of a nonperturbative quantum $S$-matrix approach. We have analytically deduced the angular differential as well as the total multiphoton rates of the proton emissions. For a linearly polarized x-ray laser field, we find that the angular distributions of proton emission sensitively depend on the laser frequency and show an interesting petal structure with increasing laser frequency as well as the number of absorbed photons. Meanwhile, we find the Coulomb repulsion potential between the proton and the remainder nucleus has a strong hindering effect on the total multiphoton rates of the proton emissions and leads to the blueshifts of the multiphoton transition frequency. Moreover, the polarization effects of laser fields on total rates of proton emission have also been addressed. We find that the polarized ellipticity corresponding to the maximum of the total rates depends on the laser frequency showing a transition from perturbative to nonperturbative proton emission. The underlying mechanism of the above findings is uncovered, and some implications are discussed.

Ab initio low-energy effective Hamiltonians for the high-temperature superconducting cuprates Bi2Sr2CuO6, Bi2Sr2CaCu2O8, HgBa2CuO4, and CaCuO2

We derive $ab$ $initio$ low-energy effective Hamiltonians (LEH) for high-temperature superconducting (SC) copper oxides Bi$_2$Sr$_2$CuO$_6$ (Bi2201, $N_{\ell}=1$, $T_c^{\rm exp} \sim 10$ K), Bi$_2$Sr$_2$CaCu$_2$O$_8$ (Bi2212, $N_{\ell}=2$, $T_c^{\rm exp} \sim 84$ K), HgBa$_2$CuO$_4$ (Hg1201, $N_{\ell}=1$, $T_c^{\rm exp} \sim 90$ K) and CaCuO$_2$ (Ca11, $N_{\ell}=\infty$, $T_c^{\rm exp} \sim 110$ K), with different experimental optimal SC transition temperature $T_c^{\rm exp}$ and number $N_{\ell}$ of laminated CuO$_2$ planes between the two neighboring block layers. We apply the latest methodology of the multiscale $ab$ $initio$ scheme for correlated electron systems (MACE), and focus on the LEH consisting of one antibonding (AB) Cu$3d_{x^2-y^2}$/O$2p_{\sigma}$ orbital centered on each Cu atom. We discuss prominent features of this LEH: (1) The ratio $U/|t_1|$ between the onsite effective Coulomb repulsion (ECR) $U$ and amplitude of nearest neighbour hopping $t_1$ increases with $T^{\rm exp}_c$ and $N_{\ell}$, consistently with the expected increase in $d$-wave SC correlation function $P_{dd}$ with $U/|t_1|$. One possible cause of the increase of $U/|t_1|$ is the replacement of apical O atoms by Cu atoms from neighbouring CuO$_2$ planes when $N_{\ell}$ increases. Furthermore, we show that the increase in distance between Cu and apical O atoms decreases the effective screening (ES) by electrons outside of the LEH and increases $U/|t_1|$. (2) For Hg1201 and Ca11, we show that $U/|t_1|$ decreases when hole doping per AB orbital $\delta$ increases, which may partly account for the disappearance of SC when $\delta$ exceeds the optimal value in experiment. (3) For $N_{\ell} \geq 2$, off-site inter-CuO$_2$ plane ECR is comparable to off-site intra-CuO$_2$ plane ECR. We discuss contributions of inter-CuO$_2$ plane ECR to both $P_{dd}$ and the stability of the SC state.

Identifying the sources of beam transmission loss of carbon isotopes

The continuous decrease of 12C beam transmission through the accelerator at high beam currents is well known. Depending on the machine design, this effect can be strong as is the case for the 250 kV SSAMS unit at CAIS. In such a case, the post acceleration 13C+/12C+ ratio of a sample is not constant, which is detrimental for online δ13C determination. In this study we attempted to identify the sources of transmission loss. We found that at high currents, 14C+/12C- ratio is not constant for a given sample but decreases linearly with increasing 12C- beam. This result is surprising because 14C being a rare isotope, its transmission is not expected to be affected during acceleration. It implies that the observed steady decline in transmission is not due to scattering effects at the stripping column but due to beam emittance growth as a result of Coulomb repulsion of the charged particles. Beam loss due to scattering by argon stripper gas is found to be independent of the beam intensity.

Transport anisotropy and metal-insulator transition in striped Dirac fermion systems

Using the determinant quantum Monte Carlo method, we investigate the metal-insulator transitions induced by the stripe of charge density in an interacting two-dimensional Dirac fermion system. The stripe will introduce the transport anisotropy and insulating intermediate phase into the system, accompanied by the change of band structure and a peak of density of states around Fermi energy. In the case of strong correlation, stripe exhibits competition with Coulomb repulsion through closing the energy gap and disrupting the magnetic order and finally drives the system in the Mott insulating phase back to the metallic state. Our results may provide a feasible way to modify transport properties by setting charge stripes in experiments.

On‐Surface Synthesis of Chiral Graphene Nanoribbon Segments via the Quarter‐Anthryl on Au(111) Surface

AbstractQuarteranthene is predicted to manifest nontrivial edge states as the competition from the hybridization of localized frontier states and the Coulomb repulsion between valence electrons, which hosts much research potential in memory, spintronic devices fabrication, and quantum computation. The fabrication of ribbon‐like structures with up‐mentioned edge states, such as chiral graphene nanoribbon, possesses a high significance in the topological phase transition investigation. However, the synthesis of chiral graphene nanoribbon is limited in reactive substrate or with the edge‐brominated precursor. Here, the fabrication of quarteranthene and its chiral graphene nanoribbon segment on Au(111) substrate is reported. A combined bond‐resolved scanning tunneling microscopy, noncontact atomic force microscopy characterization, and corresponding density functional theory calculations confirm the chemical structure of fabricated products on the Au(111) substrate. The detailed analysis of the laterally extended products reveals that the lateral‐extended structures are acquired via the linkage of the hydrocarbon quarter‐anthryl. In addition, several strategies are used to modulate the yield of quarteranthene and its lateral‐extended products. These findings provide a new insight into the lateral extension strategy on metal substrates and provide another possible fabrication strategy of chiral graphene nanoribbons on the relative inert Au(111) substrate.

Designer meron lattice on the surface of a topological insulator

We present a promising route to realize spontaneous magnetic order on the surface of a 3D topological insulator by applying a superlattice potential. The superlattice potential lowers the symmetry of the surface states and creates tunable van Hove singularities, which, when combined with strong spin-orbit coupling and Coulomb repulsion, give rise to a topological meron lattice spin texture. The periodicity of this designer meron lattice can be tuned by varying the periodicity of the superlattice potential. We employ Ginzburg-Landau theory to classify the different magnetic orders and show that the magnetic transition temperature reaches experimentally accessible values. Our work introduces another direction to realize exotic quantum order by engineering interacting Dirac electrons in a superlattice potential, with promising applications to spintronics.

Ring-like shaped charge modulations in the t−J model with long-range Coulomb interaction

The study of the charge excitations in cuprates is presently an interesting topic because of the development of new and precise x-ray experiments. Based on a large-$N$ formulation of the two-dimensional $t\text{\ensuremath{-}}J$ model, which allows us to consider all possible charge excitations on an equal footing, we investigate the charge spectrum for both electron- and hole-doped cases. In both cases, the instability toward phase separation, which has momentum modulation $\mathbf{q}=(0,0)$, is found to be robust in a large region of the doping-temperature phase diagram. If a short-range Coulomb repulsion is included the phase separation region shrinks, but the instability remains at $\mathbf{q}=(0,0)$. If on the other hand a two-dimensional long-range Coulomb interaction is included the instability sets in at $\mathbf{q}$ momenta forming a ring around $\mathbf{q}=(0,0)$. The computed charge spectrum in the translation-invariant phase shows well-formed rings. We discuss our results in the light of recent x-ray experiments in electron- and hole-doped cuprates, where ring-like shaped charge modulations have been reported.

Real-space Mott-Anderson electron localization with long-range interactions

Electrons that are delocalized in space because of quantum effects can become localized by an external disordered potential (Anderson localization) or by their mutual Coulomb repulsion (Mott/Wigner localization). A simple model addresses what happens when both effects are present, how to quantify the degree of localization, and whether approximate methods can capture the relevant physics.

Inter-configuration fluctuation for 5f electrons in uranium hexafluoride: A many-body study

A quantum mechanics calculation is performed on uranium hexafluoride (UF6) by using density functional theory (DFT) combing with dynamical mean-field theory (DMFT) scheme, taking into account the spin–orbit coupling (SOC) interaction and the on-site 5f-5f Coulomb repulsion. Results demonstrate that SOC-splitting j = 5/2 and j = 7/2 manifolds are in the metallic and insulating regimes, respectively, albeit both are in weakly correlated states. Ratio of the quasi-particle weights R = Zj=7/2/Zj=5/2 is about 1, suggesting that UF6 is not in the so-called orbital-selective localized state. Russel-Saunders (LS) coupling scheme is feasible for U 5f electrons. U 5f-conduction electrons hybridization, 5f-5f correlation, SOC interaction and final state effects yield a complicated spectrum function. Occupation probability analysis shows that 5f electrons exhibit the so-called inter-configuration fluctuation (ICF) due to admixing of 5f1 and 5f3 atomic configurations into 5f2 configuration with an average occupation number of n5f ∼ 1.8585, mainly arising from the complicated quantum mechanics processes including the dual nature of localized and itinerant 5f electrons, a quantum mechanical mixture of the energetically degenerate 5fn configurations, as well as the flexible outer electronic configuration of U ions. Finally, the momentum-resolved electronic spectrum function (the so-called quasiparticle band structure) is also discussed.

Local Kekulé distortion turns twisted bilayer graphene into topological Mott insulators and superconductors

Magic-angle twisted bilayer graphene displays at different fillings of the four flat bands lying around the charge neutrality point a wealth of notable phases that include magnetic Chern insulators, whose magnetization is mostly of an orbital nature and contiguous superconducting domes. Such a rich phase diagram is explained through the positive interplay of Coulomb repulsion and the electron coupling to a twofold optical mode that corresponds to Kekul\'e distortions localized into the small AA stacked regions of the moir\'e supercells. A static distortion stabilizes, at any integer filling of the flat bands, valence-bond insulators that carry finite Chern number away from charge neutrality. Similarly, a dynamic distortion that resonates between the two lattice vibrations leads to resonating-valence-bond topological insulators with built-in chiral d-wave pairs that have finite Chern number equal to the angular momentum, and thus are prone to turn superconducting upon doping away from integer filling.