Strong Short-range Correlations Research Articles

Event-by-event multiplicity fluctuations and correlations in ring-like and jet-like events in 197Au–AgBr collisions at 11.6 A GeV/c

Event-by-event (ebe) multiplicity fluctuations and correlations amongst the charged particles emitted in the forward–backward symmetric pseudorapidity ([Formula: see text]) windows of varying widths and positions are investigated by analyzing the experimental data on [Formula: see text]Au–AgBr collisions at 11.6[Formula: see text]A[Formula: see text]GeV/[Formula: see text]. The findings are compared with the predictions of relativistic transport model, urqmd and independent particle emission (or mixed event) model. It is observed that the fluctuations in ebe mean pseudorapidity values and those reflected from the fluctuations strength measure, [Formula: see text] are relatively higher as compared to those expected from the statistically independent particle emission model. The study of the variance, [Formula: see text] of a suitably defined forward–backward asymmetry variable [Formula: see text] as a function of [Formula: see text] window width and position indicates the presence of strong short-range correlations, which might arise due to isotropic decay of cluster-like objects either in forward or backward [Formula: see text] region. Furthermore, analyses of events having ring-like and jet-like substructures, carried out separately, suggest that the major contribution to the observed fluctuations in the data sample are due to ring-like events, while the contributions from the jet-like events appear to be rather small. The observed difference in the behavior of correlation strengths from the two types of events might be due to the enhanced emission of Cherenkov gluons, giving rise to the ring-like substructure. The mixed event analysis further confirms that the observed fluctuations are the distinct feature of the data, which disappear after event mixing.

Interplay between fractional quantum Hall liquid and crystal phases at low filling

The nature of the state at low Landau-level filling factors has been a longstanding puzzle in the field of the fractional quantum Hall effect. While theoretical calculations suggest that a crystal is favored at filling factors $\nu\lesssim 1/6$, experiments show, at somewhat elevated temperatures, minima in the longitudinal resistance that are associated with fractional quantum Hall effect at $\nu=$ 1/7, 2/11, 2/13, 3/17, 3/19, 1/9, 2/15 and 2/17, which belong to the standard sequences $\nu=n/(6n\pm 1)$ and $\nu=n/(8n\pm 1)$. To address this paradox, we investigate the nature of some of the low-$\nu$ states, specifically $\nu=1/7$, $2/13$, and $1/9$, by variational Monte Carlo, density matrix renormalization group, and exact diagonalization methods. We conclude that in the thermodynamic limit, these are likely to be incompressible fractional quantum Hall liquids, albeit with strong short-range crystalline correlations. This suggests a natural explanation for the experimentally observed behavior and a rich phase diagram that admits, in the low-disorder limit, a multitude of crystal-FQHE liquid transitions as the filling factor is reduced.

Study of the Generalized Momentum Distribution of Model Nuclear Matter

Valuable information on the correlation structure of the nuclear medium is stored in the generalized momentum distribution n(p,Q), the Fourier transform of the half-diagonal two-body density matrix ρ_{2η}(r_1,r_2,r'). In this paper, we present a numerical calculation of n(p,Q) for two Jastrow-correlated models of symmetrical nuclear matter based on the structural decomposition of n(p,Q) derived by Ristig and Clark and on a Fermi-hypernetted-chain procedure. Results exhibit significant departures from the ideal Fermi gas case in certain kinematic domains; this behaviour indicates the strong short-range correlations present in these models. Nevertheless, such deviations are less prominent than in earlier low- cluster-order calculations. The results are also used to judge the quality of Silver's approximation for n(p,Q).

Long-range and short-range ordering in 2D honeycomb-lattice magnet Na2Ni2TeO6

The magnetic structure of quasi-two-dimensional (2D) honeycomb lattice Na2Ni2TeO6 has been determined by low-temperature neutron diffraction and the crystal structure fine details at room temperature have been established by a combination of synchrotron and neutron powder diffraction. The atomic structure is described by the P63/mcm space group, but the strong presence of stacking faults defects in layered ordering is found for the first time. Both magnetization and specific heat data indicates an establishment of a long-range antiferromagnetic order with TN = 25 ± 1 K, preceded by a short-range order on 2D honeycomb lattice at about 34 K. Determined effective magnetic moment μeff = 4.35 μB is in excellent agreement with numerical estimation using effective g-factor g = 2.19 directly measured by electron spin resonance. The ground magnetic state at T = 1.5 K is represented by the commensurate zigzag-type magnetic order. Magnetic moments of Ni are almost perpendicular to the honeycomb layers, which antiferromagnetically coupled along the c-direction. Besides, the coherent magnetic scattering area has a disk shape that is homogeneous over the ab plane and compressed along the c-axis that indicates 2D nature of magnetic correlations in the compound. The magnetic diffuse neutron scattering related to the presence of strong short-range spin-spin correlations above TN was observed. Based on our experimental measurements we propose magnetic phase diagram for Na2Ni2TeO6.

Anomalous effects of Sc substitution and processing on magnetism and structure of (Gd1−xScx)5Ge4

Abstract The kinetic arrest observed in the parent Gd5Ge4 gradually vanishes when a small fraction (x = 0.025, 0.05 and 0.10) of Gd is replaced by Sc in (Gd1−xScx)5Ge4, and the magnetic ground state changes from antiferromagnetic (AFM) to ferromagnetic (FM). A first order phase transition coupled with the FM-AFM transition occurs at TC = 41 K for x = 0.05 and at TC = 53 K for x = 0.10 during heating in applied magnetic field of 1 kOe, and the thermal hysteresis is near 10 K. The first-order magnetic transition is coupled with the structural Sm5Ge4-type to Gd5Si4-type transformation. The magnetization measured as a function of applied magnetic field shows sharp metamagnetic-like behavior. At the same time, the AFM to paramagnetic transition in (Gd1−xScx)5Ge4 with x = 0.10, is uncharacteristically broad indicating development of strong short-range AFM correlations above the Neel temperature. Comparison of the magnetization data of bulk, powdered, and metal-varnish composite samples of (Gd0.95Sc0.05)5Ge4 shows that mechanical grinding and fabrication of a composite have little effect on the temperature of the first-order transformation, but short-range ordering and AFM/FM ratio below TC are surprisingly strongly affected.

Fermi surface evolution of the 2D Hubbard model within a novel four-pole approximation

We present a novel solution of the 2D Hubbard model in the framework of the Composite Operator Method within a four-pole approximation. We adopt a basis of four fields: the two Hubbard operators plus two fields describing the Hubbard transitions dressed by nearest-neighbor spin fluctuations. We include these nonlocal operators because spin fluctuations play a dominant role in strongly correlated electronic systems with respect to other types of nonlocal charge, pair and double-occupancy fluctuations. The approximate solution performs very well once compared with advanced (semi-) numerical methods from the weak-to the strong-coupling regime, being by far less computational-resource demanding. We adopt this solution to study the single-particle properties of the model in the strong coupling regime, where the effects of strong short-range magnetic correlations are more relevant and could be responsible for anomalous features. In particular, we will focus on the characterization of the Fermi surface and of its evolution with doping.

Antiferromagnetism in semiconductingSrMn2Sb2andBaMn2Sb2single crystals

Crystals of ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity $\ensuremath{\rho}$, heat capacity ${C}_{\mathrm{p}}$, and magnetic susceptibility $\ensuremath{\chi}$ measurements versus temperature $T$, and magnetization versus field $M(H)$ isotherm measurements. ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ adopts the trigonal ${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$-type structure, whereas ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ crystallizes in the tetragonal ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type structure. The $\ensuremath{\rho}(T)$ data indicate semiconducting behaviors for both compounds with activation energies of $\ensuremath{\gtrsim}0.35$ eV for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and 0.16 eV for ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$. The $\ensuremath{\chi}(T)$ and ${C}_{\mathrm{p}}(T)$ data reveal antiferromagnetic (AFM) ordering at ${T}_{\mathrm{N}}$ = 110 K for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and 450 K for ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$. The anisotropic $\ensuremath{\chi}(T\ensuremath{\le}{T}_{\mathrm{N}})$ data also show that the ordered moments in ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ are aligned in the hexagonal $ab$ plane, whereas the ordered moments in ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ are aligned collinearly along the tetragonal $c$ axis. The $ab$-plane $M(H)$ data for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ exhibit a continuous metamagnetic transition at low fields $0<H\ensuremath{\lesssim}1$ T, whereas ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ exhibits no metamagnetic transitions up to 5.5 T. The $\ensuremath{\chi}(T)$ and ${C}_{{}_{\mathrm{p}}}(T)$ data for both ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ indicate strong dynamic short-range AFM correlations above their respective ${T}_{\mathrm{N}}$ up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the ${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$ and ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$ crystal structures show that the ${T}_{\mathrm{N}}$ values for the ${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$-type compounds are much smaller than those for the ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type materials.

Natural orbital description of the halo nucleus 6He

Ab initio calculations of nuclei face the challenge of simultaneously describing strong short-range internucleon correlations and the long-range properties of weakly-bound halo nucleons. Natural orbitals, which diagonalize the one-body density matrix, provide a basis which is better matched to the physical structure of the many-body wave function. We demonstrate that the use of natural orbitals significantly improves convergence for ab initio no-core configuration interaction calculations of the neutron halo nucleus 6He, relative to the traditional oscillator basis.

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.

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.

Deep Inelastic Scattering on Ultracold Gases

We discuss Bragg scattering on both Bose and Fermi gases with strong short-range interactions in the deep inelastic regime of large wave vector transfer $q$, where the dynamic structure factor is dominated by a resonance near the free-particle energy $\hbar\omega=\varepsilon_{\bf q}=\hbar^2q^2/2m$. Using a systematic short-distance expansion, the structure factor at high momentum is shown to exhibit a nontrivial dependence on frequency characterized by two separate scaling regimes. First, for frequencies that differ from the single-particle energy by terms of order ${\cal O}(q)$ (i.e., small deviations compared to the single-particle energy), the dynamic structure factor is described by the impulse approximation of Hohenberg and Platzman. Second, deviations of order ${\cal O}(q^2)$ (i.e., of the same order or larger than the single-particle energy) are described by the operator product expansion, with a universal crossover connecting both regimes. The scaling is consistent with a number of sum rules in the large momentum limit. Furthermore, we derive an exact expression for the shift and width of the single-particle peak at large momentum due to interactions, thus extending a result by Beliaev [JETP 7, 299 (1958)] for the low-density Bose gas to arbitrary values of the scattering length $a$. The shift exhibits a maximum around $qa \simeq 1$, which is connected with a maximum in the static structure factor due to strong short-range correlations. For Bose gases with moderate interaction strengths, the theoretically predicted shift is consistent with the value observed by Papp et al. [Phys. Rev. Lett. 101, 135301 (2008)]. Finally, we develop a diagrammatic theory for the dynamic structure factor which accounts for the correlations beyond Bogoliubov theory and which covers the full range of momenta and frequencies, showing the correct asymptotic scaling at large momentum.

Strong magnetic correlations to 900 K in single crystals of the trigonal antiferromagnetic insulatorsSrMn2As2andCaMn2As2

Crystallographic, electronic transport, thermal and magnetic properties are reported for SrMn2As2 and CaMn2As2 single crystals grown using Sn flux. Rietveld refinements of powder x-ray diffraction data show that the two compounds are isostructural and crystallize in the trigonal CaAl2Si2-type structure (space group P-3m1), in agreement with the literature. Electrical resistivity rho versus temperature T measurements demonstrate insulating ground states for both compounds with activation energies of 85 meV for SrMn2As2 and 61 meV for CaMn2As2. In a local-moment picture, the Mn^{+2} 3d^5 ions are expected to have high-spin S = 5/2 with spectroscopic splitting factor g = 2. Magnetic susceptibility chi and heat capacity measurements versus T reveal antiferromagnetic (AFM) transitions at TN = 120(2) K and 62(3) K for SrMn2As2 and CaMn2As2, respectively. The anisotropic chi(T < TN) data indicate that the hexagonal c axis is the hard axis and hence that the ordered Mn moments are aligned in the ab plane. The chi(T) for both compounds and Cp(T) data for SrMn2As2 show strong dynamic short-range AFM correlations from TN up to at least 900 K, likely associated with quasi-two-dimensional connectivity of strong AFM exchange interactions between the Mn spins within the corrugated honeycomb Mn layers parallel to the ab plane.

Improving Room-Temperature Ferromagnetism in Mn-Implanted Si by High-Temperature Annealing

Mn-implanted Si with postannealing treatment at 873, 973, 1073, and 1173 K exhibited ferromagnetism at room temperature. Ferromagnetism was enhanced as the annealing temperature increased. The largest value of saturation magnetization was found in the sample annealed at 1173 K. X-ray absorption near-edge structure spectra showed no formation of substitutional–interstitial Mn–Mn dimmers in all samples. On the other hand, high-resolution transmission electron microscopy and glancing incidence X-ray diffraction revealed a variety of MnSi compounds. We propose that the ferromagnetism has the origin from the MnSi1.7 nanoparticles as well as the MnSi 1:1 phase, which possesses strong short-range spin correlation. The formation of antiferromagnetic Mn5Si3 compound in 873 and 973 K annealed samples substantially reduced the magnetism. This paper provides new insights into the understanding of ferromagnetism in Mn-implanted Si diluted magnetic semiconductors.

The Shell Model – Simplicity from Complexity

In order to apply the shell model to most nuclei, an effective ("residual") interaction between nucleons should be added to the single nucleon Hamiltonian. It cannot be the bare interaction which would introduce strong short range correlations into the shell model wave functions of nucleons moving independently in a potential well. For many years, many authors have been developing methods for calculating from the bare interaction, an effective interaction which may be used in the shell model. Only recently, the results seem to agree with experiment. During these years, successful shell model calculations have been carried out by using effective interactions determined consistently from measured energies of nuclei. Some old and some new results exhibit the success of this approach. In principle, shell model wave functions may be determined by a renormalized Hamiltonian which contains the effective interactions rather than the bare ones. Shell model wave functions may be used to calculate other observables if matrix elements are taken of renormalized operators. Such a program could succeed irrespective of the relation between shell model wave functions and the real ones. This would certainly be the case for ab initio calculations where a central potential well is not assumed and derivation of nuclear structure is attempted by using many body theory of nucleons interacting by the bare interaction. Still, there are observables which have been successfully calculated by shell model wave functions from real, un-renormalized operators. Several examples are briefly described below. This fact may be taken as some evidence that the "wounds" inflicted on shell model wave functions by the short range correlations occupy only a small volume and that there is a considerable overlap between shell model wave functions and the real ones. The calculated overlap between shell model and real wave functions may be obtained from derivations of the effective interaction. It is more difficult to see how the shell model may emerge as a good approximation from ab initio calculations. The question is whether the simplicity of the shell model as a good approximation will emerge from those complex calculations.

Properties near magnetic instability of heavy-electron compounds Ce3M4Sn13 and La3M4Sn13, with M=Co, Rh and Ru

In this review, we report the thermodynamic, magnetic and electronic transport properties of the skutterudite-related Ce3M4Sn13 and La3M4Sn13 intermetallic compounds with M = Co, Rh and Ru, which display a variety of behaviours. Ce3M4Sn13 exhibit a large increase in C/T with a maximum value of about 4 JK-2mol-1Ce due to strong electron and short-range magnetic correlations. These compounds show a crossover from a magnetically correlated heavy-fermion state to a single impurity state in applied magnetic fields. In order to study the proximity of Ce3Co4Sn13 to the possible magnetic quantum critical point (QCP), we investigated the system of Ce3-xLaxCo4Sn13 alloys. We found the critical concentration , which separates the magnetically correlated state () from a single impurity state (), however the low-T C(T)/T and the magnetic susceptibility behaviours are not characteristic of the QCP. With increasing of the magnetic field, resistivity follows power law behaviour for the samples , with n strongly field dependent. The -anomaly is discussed on the base of spin-fluctuation theory of Moriya and Takimoto. Specific heat data show that La3M4Sn13 are typical BCS superconductors, however, La3Rh4Sn13 and La3Ru4Sn13 exhibit a second superconducting phase, characteristic of inhomogeneous superconductors.

Long-range topological correlations of real polycrystalline grains in two dimensions

The topological and geometric properties of real polycrystalline grains in two dimensions are investigated on the basis of a large dataset (14,810 grains). The distribution of grain edges, the grain topology–size relationship and the short- and long-range topological correlations between neighboring grains are characterized quantitatively. The results show a strong short-range topological correlation between a center grain and its first nearest neighbors, and a trivial long-range topological correlation beyond the first nearest neighbors (on average). Both the short- and long-range relations are well described by a generalized Aboav–Weaire law reported recently. Meanwhile, it is the perimeter law, rather than the Lewis law, that describes appropriately the relationship between the topology and geometry of metallurgical grains.

Crystal electric field and the ground state properties of heavy fermion Ce3Ru4Sn13

We report on the electronic structure, electric transport and basic thermodynamic properties of the skutterudite-related Ce3Ru4Sn13 and La3Ru4Sn13. The calculated density of electronic states within the local spin density approximation (LSDA) method well fit the X-ray photoelectron spectroscopy (XPS) valence band spectra of Ce3Ru4Sn13. Magnetic susceptibility and specific heat measurements reveal that the sixfold degenerated multiplet of Ce3+ ions splits into three doublets, due to the tetragonal Ce point local symmetry in the cubic Ce3Ru4Sn13 system. Ce3Ru4Sn13 exhibits a large increase in the specific heat, C/T, data due to Kondo effect and strong electron and short-range magnetic correlations, we also suggest significant contribution of the crystal field effect. La3Ru4Sn13 is typical BCS superconductor, however, specific heat and electrical resistivity data show that La3Ru4Sn13 also exhibits a second superconducting phase at higher temperatures, which is characteristic of inhomogeneous superconductors.

Forward–backward multiplicity correlation in high-energy nucleus–nucleus interactions at a few AGeV/c

We have presented a systematic study of two-particle rapidity correlations in terms of investigating the dynamical fluctuation observable in the forward–backward pseudo-rapidity windows by analyzing the experimental data of interactions at 4.5 AGeV/c, interactions at 4.1 AGeV/c, and interactions at 4.5 AGeV/c. The experimental results have been compared with the results obtained from the analysis of event sample simulated (MC-RAND) by generating random numbers and also with the analysis of events generated by the UrQMD and AMPT model. Our study confirms the presence of strong short-range correlations among the produced particles in the forward and the backward pseudo-rapidity region. The analysis of the simple Monte Carlo-simulated (MC-RAND) events signifies that the observed correlations are not due to mere statistics only; explanation of such correlations can be attributed to the presence of dynamical fluctuations during the production of charged pions. Comparisons of the experimental results with the results obtained from analyzing the UrQMD data sample indicate that the UrQMD model cannot reproduce the experimental findings. The AMPT model also cannot explain the experimental results satisfactorily. Comparisons of our experimental results with the results obtained from the analysis of higher energy emulsion data and with the results of the RHIC data have also been presented.

Shape-induced chiral ordering in two-dimensional packing of snowmanlike dimeric particles

Understanding the distinctive phase behaviors in random packing due to particle shapes is an important issue in condensed matter physics. In this paper, we investigate the random packing structure of two-dimensional (2D) snowmen via wax-snowman packing experiments and Brownian dynamics simulations. Both experiments and simulations reveal that neighboring snowmen have a strong short-range orientational correlation and consequently locally form particular conformations. A chiral conformation is dominant for high area fractions near the jamming condition (φ>0.8), and the proportion of the chiral conformation increases with γ. We also found that the attractive interaction does not have a significant impact on the results. The geometry of chirally ordered snowmen causes a mismatch with 2D crystalline symmetries and thus inhibits the development of long-range spatial order, despite the strong orientational correlation between neighbors.

Forward–backward multiplicity fluctuations in 200A GeV/c 16O–AgBr and 32S–AgBr collisions

Charged particle multiplicity correlations and fluctuations in forward–backward symmetric pseudorapidity windows of varying widths and positions are investigated by analysing the experimental data on 16O–AgBr and 32S–AgBr collisions at 200A GeV/c. These results are compared with the predictions of the Monte Carlo models HIJING and AMPT and also with those reported at RHIC energies. The findings indicate the presence of strong short-range correlations which might arise due to isotropic decays of cluster-like objects either in the forward or backward pseudorapidity region. The analysis of the mixed events further confirms that the observed correlations are a distinct feature of the data, which vanish after mixing the events.