Short-range Correlation Effects Research Articles

Effect of short-range correlations on the single proton 3s1/2 wave function in 206Pb

We consider the experimental data for difference, Δρc(r), between the charge density distributions of the isotones 206Pb - 205Tl, deduced by analysis of elastic electron scattering measurements and corresponds to the shell model 3s1/2 proton orbit. We investigate the effects of two-body short-range correlations. This is done by: (a) Determining the corresponding single particle potential (mean-field), employing a novel method, directly from the single particle proton density and its first and second derivatives. We also carried out least-square fits to parametrized single particle potentials; (b) Determining the short-range correlations effect by employing the Jastrow correlated many-body wave function to derive a correlation factor for the single particle density distribution. The 3s1/2 wave functions of the determined potentials reproduce fairly well the experimental data within the quoted errors. The calculated charge density difference, Δρc(r), obtained with the inclusion of the short-range correlation effect does not reproduce the experimental data.

Explicitly-correlated double ionization potentials and double electron attachment equation-of-motion coupled cluster methods

Double ionization and double electron attachment equation-of-motion methods, based on linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] are formulated and implemented. An extension of double electron attachment operator is introduced for proper account of short-range correlation effects in states with two additional electrons. Numerical tests for set of doubly ionized and doubly electron attached states of several molecules have shown a good agreement between obtained explicitly-correlated results and the corresponding complete basis set limit values already at double-ζ level.

Nucleon-nucleon correlations, short-lived excitations, and the quarks within

This article reviews our current understanding of how the internal quark structure of a nucleon bound in nuclei differs from that of a free nucleon. We focus on the interpretation of measurements of the EMC effect for valence quarks, a reduction in the Deep Inelastic Scattering (DIS) cross-section ratios for nuclei relative to deuterium, and its possible connection to nucleon-nucleon Short-Range Correlations (SRC) in nuclei. Our review and new analysis (involving the amplitudes of non-nucleonic configurations in the nucleus) of the available experimental and theoretical evidence shows that there is a phenomenological relation between the EMC effect and the effects of SRC that is not an accident. The influence of strongly correlated neutron-proton pairs involving highly virtual nucleons is responsible for both effects. These correlated pairs are temporary high-density fluctuations in the nucleus in which the internal structure of the nucleons is briefly modified. This conclusion needs to be solidified by the future experiments and improved theoretical analyses that are discussed herein.

Modeling pion production in heavy-ion collisions at intermediate energies

Pion production in nucleus-nucleus collisions at intermediate energies was modeled in the framework of the Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model. The effects of nucleon-nucleon short-range correlations in initialization and mean-field potential, isospin-dependent in-medium baryon-baryon elastic and inelastic cross sections and pion in-medium effect are all considered in this model. It is found that the ratio and yields of $\pi^{-}$and $\pi^{+}$ in Au+Au reaction at 400 MeV/nucleon reproduce the FOPI/GSI data very well especially with a soft symmetry energy in the present transport model. Predictions on the single and double $\pi^{-}/\pi^{+}$ ratio are made for the isotope reaction systems $^{132}\rm {Sn}+^{124}\rm {Sn}$ and $^{108}\rm {Sn}+^{112}\rm {Sn}$ at 300 MeV/nucleon since related experiments are being carried out at RIKEN/Japan.

Effect of the collective motions of molecules inside a condensed phase on fluctuations in the density of small bodies

An approach to calculating the effects of fluctuations in density that considers the collective motions of molecules in small condensed phases (e.g., droplets, microcrystals, adsorption at microcrystal faces) is proposed. Statistical sums of the vibrational, rotational, and translational motions of molecules are of a collective character expressed in the dependences of these statistical sums on the local configurations of neighboring molecules. This changes their individual contributions to the free energy and modifies fluctuations in density in the inner homogeneous regions of small bodies. Interactions between nearest neighbors are considered in a quasi-chemical approximation that reflects the effects of short-range direct correlations. Expressions for isotherms relating the densities of mixture components to the chemical potentials in a thermostat are obtained, along with equations for pair distribution functions.

Three-Nucleon Forces and Triplet Pairing in Neutron Matter

The existence of superfluidity of the neutron component in the core of a neutron star, associated specifically with triplet $P-$wave pairing, is currently an open question that is central to interpretation of the observed cooling curves and other neutron-star observables. Ab initio theoretical calculations aimed at resolving this issue face unique challenges in the relevant high-density domain, which reaches beyond the saturation density of symmetrical nuclear matter. These issues include uncertainties in the three-nucleon (3N) interaction and in the effects of strong short-range correlations -- and more generally of in-medium modification of nucleonic self-energies and interactions. A survey of existing solutions to the gap equations in the triplet channel shows that the separate or combined impacts of 3N forces, coupled channels, and mass renormalization range from moderate to strong to devastating, thus motivating a detailed analysis of the competing effects. In the present work we track the effects of the 3N force and in-medium modifications in the representative case of the $^3P_2$ channel, based on the Argonne V18 two-nucleon (2N) interaction supplemented by 3N interactions of the Urbana IX family. Sensitivity of the results to the input interaction is clearly demonstrated, while consistency issues arise with respect to the simultaneous treatment of 3N forces and in-medium effects. We consider this pilot study as the first step towards a systematic and comprehensive exploration of coupled-channel $^3P F_2$ pairing using a broad range of 2N and 3N interactions from the current generation of refined semi-phenomenological models and models derived from chiral effective field theory.

The role of short-range magnetic correlations in the gap opening of topological Kondo insulators

In this article we investigate the effects of short-range anti-ferromagnetic correlations on the gap opening of topological Kondo insulators. We add a Heisenberg term to the periodic Anderson model at the limit of strong correlations in order to allow a small degree of hopping of the localized electrons between neighboring sites of the lattice. This new model is adequate for studying topological Kondo insulators, whose paradigmatic material is the compound . The main finding of the article is that the short-range antiferromagnetic correlations, present in some Kondo insulators, contribute decisively to the opening of the Kondo gap in their density of states. These correlations are produced by the interaction between moments on the neighboring sites of the lattice.For simplicity, we solve the problem on a two dimensional square lattice. The starting point of the model is the ions orbitals, with multiplet in the presence of spin–orbit coupling. We present results for the Kondo and for the antiferromagnetic correlation functions. We calculate the phase diagram of the model, and as we vary the level position from the empty regime to the Kondo regime, the system develops metallic and topological Kondo insulator phases. The band structure calculated shows that the model describes a strong topological insulator.

Tensor correlations in light nuclei with tensor-optimized antisymmetrized molecular dynamics

We investigate the light nuclei using the nucleon-nucleon interaction. We describe the tensor and short-range correlations with the new variational theory named “tensor-optimized antisymmetrized molecular dynamics” (TOAMD). In TOAMD, the correlation functions for the tensor force FD and the short-range repulsion FS and their multiples are multiplied to the AMD wave function and the total wave function is expressed as the sum of all the components. We take all the necessary matrix elements of many-body operators coming from the products of the multiple correlation functions and the Hamiltonian. We use the interaction AV8′ and discuss the effect of tensor and short-range correlations in the s-shell nuclei, 3H and 4He.

Coarse-grained short-range correlations

We develop a scheme to take into account the effects of short-range nucleon-nucleon correlations in the nucleon-pair wave function by solving the Bethe-Goldstone equation for a coarse grained delta shell potential in S-wave configuration. The S-wave delta shell potential has been adjusted to reproduce the $^1$S$_0$ phase shifts of the AV18 potential for this partial wave up to 2 GeV in the laboratory kinetic energy. We show that a coarse grained potential can describe the high momentum tail of the back-to-back correlated pairs and the $G$-matrix in momentum space. We discuss the easiness and robustness of the calculation in coordinate space and the future improvements and utilities of this model. This work suggests the possibility of using perturbation theory for describing the short-range correlations, and related to this, to substitute the $G$-matrix by an appropriate coarse-grained potential.

Microscopic nucleon spectral function for finite nuclei featuring two- and three-nucleon short-range correlations: The model versus ab initio calculations for three-nucleon systems

The main features of the convolution model which, in the region of two-nucleon (2N) and three-nucleon (3N) short-range correlations (SRC), describes the one-nucleon momentum distribution n(k_1) and the spectral function P(k_1,E) in terms of a convolution integral involving the relative n_{rel}(k_{rel}) and the center-of-mass n_{c.m.}(K_{c.m.}) momentum distributions of a nucleon-nucleon pair, are illustrated in detail. It is stressed that the model, which stems from the universal property of factorization exhibited by the nuclear wave function at short inter-nucleon distances, is only applicable in a well-defined region of k_{rel} and K_{c.m.}; it is shown, in particular, that the requirement of factorization introduces a severe constraint on the values of k_{rel} and K_{c.m.} that appear in the convolution integral. Using ab-initio relative and c.m. momentum distributions for ^3He, the validity of the convolution model is investigated by comparing the model spectral function and momentum distributions with the ones resulting from ab-initio calculations performed with realistic local NN interaction of the Argonne family. It is shown that when the constraint on the value of k_{rel} and K_{c.m.} are correctly taken into account and only 2N SRC are taken into account, the convolution model is in good agreement with the ab-initio spectral function in the region of the peak exhibited by the latter, whereas far from the peak, particularly at high values of the removal energy, the model spectral function can be qualitatively reconciled with the ab-initio spectral function only by considering the effects of 3N SRC. As for the nucleon momentum distribution, the effects of 3N SRC appears to be very small.

Magnetization and Neutron Diffraction Studies on Nanocrystalline Tetragonal SrFeO3−δ

Magnetization, AC susceptibility and neutron diffraction measurements are carried out on a nanocrystalline tetragonal SrFeO3−δ system prepared through solid-state reaction. Observed coercivity is due to uncompensated spins from the surface of the nanoparticle and broken bonds at the surface. Finite size effect plays a major role in hysteresis. The irreversibility in magnetization above the Neel temperature (TN) is due to the short-range correlation effect and the presence of local anisotropy field. Based on magnetization, AC susceptibility and neutron diffraction studies, we conclude that the nanocrystalline tetragonal SrFeO3−δ is an antiferromagnet with Neel temperature around 79 K.

Simulation of the NMR response in the pseudogap regime of the cuprates

The pseudogap in the cuprate high-temperature superconductors was discovered as a suppression of the Knight shift and spin relaxation time measured in nuclear magnetic resonance (NMR) experiments. However, theoretical understanding of this suppression in terms of the magnetic susceptiblility of correlated itinerant fermion systems was so far lacking. Here we study the temperature and doping evolution of these quantities on the two-dimensional Hubbard model using cluster dynamical mean field theory. We recover the suppression of the Knight shift and the linear-in-T spin echo decay that increases with doping. The relaxation rate shows a marked increase as T is lowered but no indication of a pseudogap on the Cu site, and a clear downturn on the O site, consistent with experimental results on single layer materials but different from double layer materials. The consistency of these results with experiment suggests that the pseudogap is well described by strong short-range correlation effects.

Counterion effect on the spin-transition properties of the second generation iron(III) dendrimeric complexes

The magnetic properties and the influence of counterions on the spin crossover properties of two novel Fe(III) dendrimeric complexes of the second generation, namely [Fe(L)2]+X−, where L=3,5-di(3,4,5-tris(tetradecyloxy)benzoyloxy)benzoyl-4-oxy-salicylidene-N’-ethyl-N-ethylenediamine X=Cl− (1), ClO4− (2), have been studied for the first time by magnetic susceptibility measurements and electron paramagnetic resonance (EPR) method in a wide (4.2–300K) temperature range. EPR results showed that compound 1 contains about 98% of high-spin (HS, S=5/2) and ∼2% of low-spin (LS, S=1/2) Fe(III) centers, and undergoes an antiferromagnetic ordering below 7K. The EPR integrated intensity of a broad line (g≈2), corresponding to the HS iron(III) centers, passes through a broad maximum at Tmax≈100K, which is indicative of short-range correlation effects. The anomalous broadening of this EPR line at low temperatures with the critical exponent β=1.5 upon approaching the long-range ordering transition (TNEPR=7K) from above indicates the quasi-two-dimensional antiferromagnetic nature of magnetism in complex 1. The spin-crossover effect is completely suppressed in compound 1. The complex with ClO4− counterion demonstrates a different magnetic behavior. EPR data showed that compound 2 contains about 77% of LS and ∼23% of HS Fe(III) centers at TNEPR=10.2K. It displays a partial spin crossover (S=5/2↔1/2) above 150K and undergoes the antiferromagnetic ordering below 10.2K. The obtained results and the results of DFT calculations allowed us to conclude that a bilayered packing with a chain structure of Fe(III) centers in ionic bilayers is formed in compound 1, whereas a dimeric structure of Fe(III) centers is formed in compound 2. Thus, the ability of the counterion to form an effective network of hydrogen bonds and its size define the packing motif of the [Fe(L)2]+ complexes. Therefore, the replacing of the counterion has a significant impact on the magnetic properties of the compound.

Nuclear matrix element of neutrinoless double-βdecay: Relativity and short-range correlations

Background: The discovery of neutrinoless double-beta ($0\nu\beta\beta$) decay would demonstrate the nature of neutrinos, have profound implications for our understanding of matter-antimatter mystery, and solve the mass hierarchy problem of neutrinos. The calculations for the nuclear matrix elements $M^{0\nu}$ of $0\nu\beta\beta$ decay are crucial for the interpretation of this process. Purpose: We study the effects of relativity and nucleon-nucleon short-range correlations on the nuclear matrix elements $M^{0\nu}$ by assuming the mechanism of exchanging light or heavy neutrinos for the $0\nu\beta\beta$ decay. Methods: The nuclear matrix elements $M^{0\nu}$ are calculated within the framework of covariant density functional theory, where the beyond-mean-field correlations are included in the nuclear wave functions by configuration mixing of both angular-momentum and particle-number projected quadrupole deformed mean-field states. Results: The nuclear matrix elements $M^{0\nu}$ are obtained for ten $0\nu\beta\beta$-decay candidate nuclei. The impact of relativity is illustrated by adopting relativistic or nonrelativistic decay operators. The effects of short-range correlations are evaluated. Conclusions: The effects of relativity and short-range correlations play an important role in the mechanism of exchanging heavy neutrinos though the influences are marginal for light neutrinos. Combining the nuclear matrix elements $M^{0\nu}$ with the observed lower limits on the $0\nu\beta\beta$-decay half-lives, the predicted strongest limits on the effective masses are $|\langle m_\nu\rangle|<0.06~\mathrm{eV}$ for light neutrinos and $|\langle m_{\nu_h}^{-1}\rangle|^{-1}>3.065\times 10^8~\mathrm{GeV}$ for heavy neutrinos.

Proton skins in momentum space and neutron skins in coordinate space in heavy nuclei

Neutron-skins in coordinate space and proton-skins in momentum space are predicted to coexist in heavy nuclei and their correlation is governed by Liouville's theorem and Heisenberg's uncertainty principle. An analysis of their correlation within a further extended Thomas-Fermi (ETF$^+$) approximation incorporating effects of nucleon short-range correlations reveals generally that protons move faster than neutrons in neutron-skins of heavy nuclei.

Nonequilibrium dynamical cluster approximation study of the Falicov-Kimball model

We use a nonequilibrium implementation of the dynamical cluster approximation (DCA) to study the effect of short-range correlations on the dynamics of the two-dimensional Falicov-Kimball model after an interaction quench. As in the case of single-site dynamical mean field theory, thermalization is absent in DCA simulations, and for quenches across the metal-insulator boundary, nearest-neighbor charge correlations in the nonthermal steady state are found to be larger than in the thermal state with identical energy. We investigate to what extent it is possible to define an effective temperature of the trapped state after a quench. Based on the ratio between the lesser and retarded Green's function we conclude that a roughly thermal distribution is reached within the energy intervals corresponding to the momentum-patch dependent subbands of the spectral function. The effectively different chemical potentials of these distributions however lead to a very hot, or even negative, effective temperature in the energy intervals between these subbands.

QCD corrections and long-range mechanisms of neutrinoless double beta decay

Recently it has been demonstrated that QCD corrections are numerically important for short-range mechanisms (SRM) of neutrinoless double beta decay ($0\nu\beta\beta$) mediated by heavy particle exchange. This is due to the effect of color mismatch for certain effective operators, which leads to mixing between different operators with vastly different nuclear matrix elements (NMEs). In this note we analyze the QCD corrections for long-range mechanisms (LRM), due to diagrams with light-neutrino exchange between a Standard Model (V-A)$\times$(V-A) and a beyond the SM lepton number violating vertex. We argue that in contrast to the SRM in the LRM case, there is no operator mixing from color-mismatched operators. This is due to a combined effect of the nuclear short-range correlations and color invariance. As a result, the QCD corrections to the LRM amount to an effect no more than 60%, depending on the operator in question. Although less crucial, taken into account QCD running makes theoretical predictions for $0\nu\beta\beta$-decay more robust also for LRM diagrams. We derive the current experimental constraints on the Wilson coefficients for all LRM effective operators.

Short-Range Order and Correlation Effects in Solid Solutions

The results of statistical theory in quasichemical approximation of long- and short-range atomic ordering in ternary substitutional solid solutions AB3 + C with a face-centered cubic (FCC) lattice L12 of a Cu 3 Au type suggesting that atoms C are arranged in the sites of both types legal for atoms A and B are given. For particular cases, the formulas of the parameters characterizing short-range ordering depending on the temperature, the alloy composition, the degree of long-range order, and the energy constants are given. The character of their functional dependences is determined, the graphs are constructed. The calculation results correlate with the experimental data published.

Short-Range Electron Correlation Stabilizes Noncavity Solvation of the Hydrated Electron.

The hydrated electron, e-(aq), has often served as a model system to understand the influence of condensed-phase environments on electronic structure and dynamics. Despite over 50 years of study, however, the basic structure of e-(aq) is still the subject of controversy. In particular, the structure of e-(aq) was long assumed to be an electron localized within a solvent cavity, in a manner similar to halide solvation. Recently, however, we suggested that e-(aq) occupies a region of enhanced water density with little or no discernible cavity. The potential we developed was only subtly different from those that give rise to a cavity solvation motif, which suggests that the driving forces for noncavity solvation involve subtle electron-water attractive interactions at close distances. This leads to the question of how dispersion interactions are treated in simulations of the hydrated electron. Most dispersion potentials are ad hoc or are not designed to account for the type of close-contact electron-water overlap that might occur in the condensed phase, and where short-range dynamic electron correlation is important. To address this, in this paper we develop a procedure to calculate the potential energy surface between a single water molecule and an excess electron with high-level CCSD(T) electronic structure theory. By decomposing the electron-water potential into its constituent energetic contributions, we find that short-range electron correlation provides an attraction of comparable magnitude to the mean-field interactions between the electron and water. Furthermore, we find that by reoptimizing a popular cavity-forming one-electron model potential to better capture these attractive short-range interactions, the enhanced description of correlation predicts a noncavity e-(aq) with calculated properties in better agreement with experiment. Although much attention has been placed on the importance of long-range dispersion interactions in water cluster anions, our study reveals that largely unexplored short-range correlation effects are crucial in dictating the solvation structure of the condensed-phase hydrated electron.

Driven Interfaces: From Flow to Creep Through Model Reduction

The response of spatially extended systems to a force leading their steady state out of equilibrium is strongly affected by the presence of disorder. We focus on the mean velocity induced by a constant force applied on one-dimensional interfaces. In the absence of disorder, the velocity is linear in the force. In the presence of disorder, it is widely admitted, as well as experimentally and numerically verified, that the velocity presents a stretched exponential dependence in the force (the so-called 'creep law'), which is out of reach of linear response, or more generically of direct perturbative expansions at small force. In dimension one, there is no exact analytical derivation of such a law, even from a theoretical physical point of view. We propose an effective model with two degrees of freedom, constructed from the full spatially extended model, that captures many aspects of the creep phenomenology. It provides a justification of the creep law form of the velocity-force characteristics, in a quasistatic approximation. It allows, moreover, to capture the non-trivial effects of short-range correlations in the disorder, which govern the low-temperature asymptotics. It enables us to establish a phase diagram where the creep law manifests itself in the vicinity of the origin in the force--system-size--temperature coordinates. Conjointly, we characterise the crossover between the creep regime and a linear-response regime that arises due to finite system size.