Many-body Correlation Effects Research Articles

Polarizable polymer chain under external electric field: Effects of many-body electrostatic dipole correlations.

We present a new simple self-consistent field theory of a polarizable flexible polymer chain under an external constant electric field with account for the many-body electrostatic dipole correlations. We show the effects of electrostatic dipole correlations on the electric-field-induced globule-coil transition. We demonstrate that only when the polymer chain is in the coil conformation, the electrostatic dipole correlations of monomers can be considered as pairwise. However, when the polymer chain is in a collapsed state, the dipole correlations have to be considered at the many-body level.

Electron spin resonance in a two-dimensional Fermi liquid with spin-orbit coupling

Electron spin resonance (ESR) is usually interpreted as a single-particle phenomenon protected from the effect of many-body correlations. We show that this is not the case in a two-dimensional Fermi liquid (FL) with spin-orbit coupling (SOC). Depending on whether the magnetic field is below or above some critical value, ESR in such a system probes up to three collective chiral-spin modes, augmented by the presence of the field, or the Larmor mode, augmented both by SOC and FL renormalizations. We argue that ESR can be used as a probe not only for SOC but also for many-body physics.

Development of the Multicomponent Coupled-Cluster Theory for Investigation of Multiexcitonic Interactions.

Multicomponent systems are defined as chemical systems that require a quantum mechanical description of two or more different types of particles. Non-Born-Oppenheimer electron-nuclear interactions in molecules, electron-hole interactions in electronically excited nanoparticles, and electron-positron interactions are examples of physical systems that require a multicomponent quantum mechanical formalism. The central challenge in the theoretical treatment of multicomponent systems is capturing the many-body correlation effects that exist not only between particles of identical types (electron-electron) but also between particles of different types (electron-nuclear and electron-hole). In this work, the development and implementation of multicomponent coupled-cluster (mcCC) theory for treating particle-particle correlation in multicomponent systems are presented. This method provides a balanced treatment of many-particle correlation effects in a general multicomponent system while maintaining a size-consistent and size-extensive formalism. The coupled-cluster ansatz presented here is an extension of the electronic structure CCSD formulation for multicomponent systems and is defined as |ΨmcCC⟩ = eT1I+T2I+T1II+T2II+T11I,II+T12I,II+T21I,II+T22I,II|0I0II⟩. The cluster amplitudes in the mcCC wave function were obtained by projecting the mcCC Schrödinger equation onto a direct product space of singly and doubly excited states of type I and II particles and then solving the resulting mcCC equations iteratively. These equations were derived using an automated application of the generalized Wick’s theorem and were implemented using a computer-assisted source code generation approach. The applicability of the mcCC method was demonstrated by calculating ground state energies of multicomponent Hooke's atom and positronium hydride systems as well as by calculating exciton and biexciton binding energies in multiexcitonic systems. For each case, the mcCC results were benchmarked against full configuration interaction (FCI) calculations and were found to be in excellent agreement with the FCI results. The effect of neglecting certain classes of multicomponent connected excitation terms from the mcCC wave function was also investigated. The results from this study demonstrate that connected cluster operators that generate simultaneous excitation in type I and type II space are critical for capturing electron-hole correlation in multiexcitonic systems.

Tunable electronic correlation effects in nanotube-light interactions

Electronic many-body correlation effects in one-dimensional (1D) systems such as carbon nanotubes have been predicted to strongly modify the nature of photoexcited states. Here we directly probe this effect using broadband elastic light scattering from individual suspended carbon nanotubes under electrostatic gating conditions. We observe significant shifts in optical transition energies, as well as line broadening, as the carrier density is increased. The results demonstrate the role of screening of many-body electronic interactions on the different length scales, a feature inherent to quasi-1D systems. Our findings further demonstrate the possibility of electrical tuning of optical transitions and provide a basis for understanding of various optical phenomena in carbon nanotubes and other quasi-1D systems in the presence of charge carrier doping.

Degenerate limit thermodynamics beyond leading order for models of dense matter

Analytical formulas for next-to-leading order temperature corrections to the thermal state variables of interacting nucleons in bulk matter are derived in the degenerate limit. The formalism developed is applicable to a wide class of non-relativistic and relativistic models of hot and dense matter currently used in nuclear physics and astrophysics (supernovae, proto-neutron stars and neutron star mergers) as well as in condensed matter physics. We consider the general case of arbitrary dimensionality of momentum space and an arbitrary degree of relativity (for relativistic models). For non-relativistic zero-range interactions, knowledge of the Landau effective mass suffices to compute next-to-leading order effects, but for finite-range interactions, momentum derivatives of the Landau effective mass function up to second order are required. Results from our analytical formulas are compared with the exact results for zero- and finite-range potential and relativistic mean-field theoretical models. In all cases, inclusion of next-to-leading order temperature effects substantially extends the ranges of partial degeneracy for which the analytical treatment remains valid. Effects of many-body correlations that deserve further investigation are highlighted.

Second-quantized surface hopping.

The trajectory surface hopping method for quantum dynamics is reformulated in the space of many-particle states to include entanglement and correlation of trajectories. Used to describe many-body correlation effects in electronic structure theories, second quantization is applied to semiclassical trajectories. The new method allows coupling between individual trajectories via energy flow and common phase evolution. It captures the properties of a wave packet, such as branching, Heisenberg uncertainty, and decoherence. Applied to a superexchange process, the method shows very accurate results, comparable to exact quantum data and improving greatly on the standard approach.

Many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells

The many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells are investigated. A special case of the many-component electron–hole system is considered. It is shown that if the hole mass is much greater than the electron mass, the negative correlation energy is mainly determined by the holes. The ground state of the system is found to be the 2D electron–hole liquid with the energy smaller than the exciton phase. It is shown that the system decays into the spatially separated neutral electron–hole drops if the initially created charge density in the layers is smaller than the certain critical value neq.

Exciton Gas versus Electron Hole Liquid in the Double Quantum Wells

ABSTRACTThe many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells (CQW) are investigated. A special case of the many-component electron-hole system is considered, ν>>1 being the number of the components. Keeping the main diagrams in the parameter 1/ν allows us to justify the selection of the RPA diagrams. The ground state of the system is found to be the electron-hole liquid with the energy smaller than the dense exciton gas phase. The possible connection is discussed between the results obtained and the experiments in which the inhomogeneous state in the CQW is found.

Momentum distribution and Compton profile by theab initioGW approximation

We present two possible approaches to calculate the momentum distribution $n(p)$ and the Compton profile within the framework of the ab initio GW approximation on the self-energy. The approaches are based on integration of the Green's function along either the real or the imaginary axes. Examples will be presented on the jellium model and on real bulk sodium. Advantages and drawbacks of both methods are discussed in comparison with accurate quantum Monte Carlo calculations and x-ray Compton scattering experiments. We illustrate the effect of many-body correlations and disentangle them from band-structure and anisotropy effects by a comparison with density functional theory in the local density approximation. Our results suggest the use of ${\text{G}}_{0}{\text{W}}_{0}$ momentum distributions as reference for future experiments and theory developments.

Rectification in substituted atomic wires: a theoretical insight

Recently, there have been discussions that the giant diode property found experimentally in diblock molecular junctions could be enhanced by the many-body electron correlation effect beyond the mean field theory. In addition, the effect of electron–phonon scattering on an electric current through the diode molecule, measured by inelastic tunneling spectroscopy (IETS), was found to be symmetric with respect to the voltage sign change even though the current is asymmetric. The reason for this behavior is a matter of speculation. In order to clarify whether or not this feature is limited to organic molecules in the off-resonant tunneling region, we discuss the current asymmetry effect on IETS in the resonant region. We introduced heterogeneous atoms into an atomic wire and found that IETS becomes asymmetric in this substituted atomic wire case. Our conclusion gives the other example of intrinsic differences between organic molecules and metallic wires. While the contribution of electron–phonon scattering to IETS is not affected by the current asymmetry in the former case, it is affected in the latter case. The importance of the contribution of the electron–hole excitation to phonon damping in bringing about the current asymmetry effect in IETS in the latter case is discussed.

Gas‐Phase Thermodynamics as a Validation of Computational Catalysis on Surfaces: A Case Study of Fischer–Tropsch Synthesis

Density functional theory has become a valuable tool to study surface catalysis. However, due to the scarcity of clean and reliable experimental data on surfaces, the theoretical methods employed to explore heterogeneous catalytic mechanisms are usually less well validated than those for gas-phase reactions. We argue herein that gas-phase reactions and the corresponding surface reactions are related through the Born-Haber cycle and computational catalysis on surfaces will be less meaningful if gas-phase behavior cannot first be suitably determined. In this contribution, we have constructed a set of gas-phase reactions relevant to the Fischer-Tropsch synthesis as a case study. With this set, we have tested the validity of the widely used PBE and B3LYP functionals and found that neither of them are capable of describing all kinds of gas-phase reactions properly, such that some surface reactions may be biased falsely against the others. Significantly, XYG3, which is a double-hybrid functional that includes Hartree-Fock-like exchange and many-body perturbation correlation effects, presents a significant improvement for all of the gas-phase reactions, holding promise for further development for surface catalysis.

Effect of many-body correlations on mesoscopic charge relaxation

We investigate nonperturbatively the charge relaxation resistance and quantum capacitance in a coherent $\mathit{RC}$ circuit in the strong-coupling regime. We find that the many-body correlations break the universality in the charge relaxation resistance: (i) The charge relaxation resistance has peaks at finite frequencies ${\ensuremath{\Gamma}}^{*}/\ensuremath{\hbar}$, where ${\ensuremath{\Gamma}}^{*}$ is an effective level broadening, and (ii) the zero-frequency resistance deviates from the universal value when the Zeeman splitting is comparable to ${\ensuremath{\Gamma}}^{*}$. This behavior becomes even more prominent in the Kondo regime. The observed features are ascribed to the generation of particle-hole excitations in the contacts accomplished by spin-flip processes in the dot.

Effects of observation on quantum interference in a laterally coupled double quantum dot using a quantum dot charge sensor

We theoretically investigated the effects of the observation by a quantum dot charge sensor on an Aharonov–Bohm effect in a laterally coupled double quantum dot using the interpolative 2nd-order perturbation theory. In particular, we introduce the notion of the coherent indirect coupling, which characterizes the strength of the indirect coupling between two quantum dots via the reservoir. As the Coulomb interaction V S for the charge sensing increases, the linear conductance through a double quantum dot decreases because of the many-body correlation effect. The visibility of Aharonov–Bohm oscillation in the linear conductance behaves super-linearly for weak sensing interaction regime and sub-linearly for strong sensing interaction regime.

Temperature dependence of exciton complexes photoluminescence spectra in self-assembled InAs/GaAs quantum rings

We investigate the temperature dependent photoluminescence (PL) spectra of exciton complexes in the self-assembled InAs/GaAs quantum rings (QRs) by using an atomistic pseudopotential method and a configuration-interaction treatment of many-particle effects. We find, unlike in quantum dots, the biexciton XX and positive trion X+ in QRs show multitransition peaks even at very low temperatures, and the PL spectra are very sensitive to the temperature. The peculiar temperature dependent spectra of XX and X+ is due to the unique electronic structures and the strong many-body correlation effects in the QRs.

Gamow shell-model calculations of drip-line oxygen isotopes

We employ the Gamow shell model (GSM) to describe low-lying states of the oxygen isotopes $^{24}\mathrm{O}$ and $^{25}\mathrm{O}$. The many-body Schr\odinger equation is solved starting from a two-body Hamiltonian defined by a renormalized low-momentum nucleon-nucleon ($\mathit{NN}$) interaction and a spherical Berggren basis. The Berggren basis treats bound, resonant, and continuum states on an equal footing and is therefore an appropriate representation of loosely bound and unbound nuclear states near threshold. We show that the inclusion of continuum effects has a significant effect on the low-lying ${1}^{+}$ and ${2}^{+}$ excited states in $^{24}\mathrm{O}$. On the other hand, we find that a correct description of binding energy systematics of the ground states is driven by the proper treatment and inclusion of many-body correlation effects. This is supported by the fact that we get $^{25}\mathrm{O}$ unstable with respect to $^{24}\mathrm{O}$ in both oscillator and Berggren representations starting from a $^{22}\mathrm{O}$ core. Furthermore, we show that the structure of these loosely bound or unbound isotopes is strongly influenced by the ${}^{1}{S}_{0}$ component of the $\mathit{NN}$ interaction. This has important consequences for our understanding of nuclear stability.

Coherent Multidimensional Optical Probes for Electron Correlations and Exciton Dynamics: From NMR to X-rays

Over the past 15 years, researchers have extended the multidimensional techniques which originated with NMR in the 1970s to infrared and visible coherent spectroscopy. These advances have dramatically enhanced the temporal resolution from the microsecond to the femtosecond regime. NMR spectroscopists have developed principles for the design of pulse sequences that enhance selected spectral features and reveal desired dynamical events. Extending these principles to the optical regime offers numerous opportunities for narrowing the line shapes in specific directions, unraveling weak cross-peaks from otherwise congested spectra, and controlling the interferences between quantum pathways. We can achieve these enhancements by shaping the spectral and temporal profiles of the pulses. Pulse polarization shaping may lead to unique probes of time-dependent chirality. In this Account, we compare two types of signals. The first, the photon echo, is generated in the direction -k(1) + k(2) + k(3), and the second, double quantum coherence, is detected at +k(1) + k(2) - k(3). Here k(1), k(2), and k(3) are the wave vectors of the three incoming pulses in chronological order. We illustrate the novel information extracted from these signals by simulations of three physical systems. In the first system, spectra of GaAs semiconductor quantum wells provide a direct look at many-body electron correlation effects. We directly observe specific projections of the many-electron wave function, which we can use to test the quality of various levels of computational techniques for electronic structure. Secondly, the spectra of photosynthetic aggregates reveal couplings between chromophores, quantum coherence signatures of chromophore entanglement, and energy-transfer pathways. Using some fundamental symmetries of pulse polarization configurations of nonlinear signals, we can construct superpositions of signals designed to better distinguish among various coherent and incoherent exciton transport pathways and amplify subtle variations among different species of the Fenna-Matthews-Olson (FMO) antenna complex. Both of the first two applications require femtosecond pulses of light in the visible range. The third application demonstrates how resonant core spectroscopy may be used to generate core excitations that are highly localized at selected atoms. Such signals can monitor the motions of valence electron wavepackets in real space with atomic spatial resolution. These future X-ray applications will require attosecond bright X-ray sources, which are currently being developed in several labs. Common principles underlie these techniques in coherent spectroscopy for spins, valence electrons, and core electronic excitations, spanning frequencies from radiowaves to hard X-rays.

Effect of many-body quantum fluctuations on matrix Berry phases of a two-dimensionaln-type semiconductor quantum dot

In the presence of spin–orbit coupling and inversion symmetry of the lateral confinementpotential a single electron does not exhibit matrix Berry phases in quasi-two-dimensionalsemiconductor quantum dots. In such a system we investigate whether many-bodycorrelation effects can lead to finite matrix Berry phases. We find that the transformationproperties of many-electron wavefunctions under two-dimensional inversion operation donot allow finite matrix Berry phases. This effect is exact and is independent of the form ofelectron–electron interactions. On the other hand, quasi-two-dimensional semiconductorquantum dots with lateral confinement potential without inversion symmetry can havefinite matrix Berry phases. We find that many-body quantum fluctuations can changematrix Berry phases significantly in such systems.

A statistical-mechanical theory of self-diffusion in colloidal suspensions — application to colloidal glass transitions

A statistical-mechanical theory of self-diffusion in colloidal suspensions is presented. A renormalized linear Langevin equation is derived from a nonlinear Langevin equation by employing the Tokuyama–Mori projection operator method. The friction constant is thus shown to be renormalized by the many-body correlation effects due to not only the direct interactions between particles, but also due to the hydrodynamic interactions between particles. The equations for the mean-square displacement and the non-Gaussian parameter are then derived. The present theory is applied to colloidal glass transitions to discuss the crossover phenomena in the dynamics of a single particle from a short-time self-diffusion process to a long-time self-diffusion process via a β (caging) stage. The effects of the renormalized friction coefficient on self-diffusion are thus explored with the aid of the analyses of the experimental data and the simulation results by the mean-field theory proposed by the present author. It is thus shown that the relaxation time of the renormalized memory function is given by the β -relaxation time. It is also shown that the non-Gaussian parameter is very small, even near the glass transition, because of the existence of the short-time self-diffusion coefficient caused by the hydrodynamic interactions.

Many-body interactions between ions in LiH crystal and its equation of state under high pressure

When the cohesive energy of LiH is calculated, the many-body correlation effect between ions and the contraction of ionic orbital are included, as two separate physical mechanisms in the total energy formula. The exchange-energy between electronic orbitals is directly computed without any adjustable parameters introduced. The results showed that many-body exchange-correlation effects markedly influence the properties at zero pressure and under high pressures. When the contributions of the nearest and next-nearest ions were taken into account, the results of the isothermal equation of state is in good agreement with experimental data in the pressure range of 0—90 GPa.

Exchange and correlation effect on spin Coulomb drag in a quasi-two-dimensional electron system

We investigate the effect of many-body electronic correlations on spin Coulomb drag (SCD) beyond the random phase approximation (RPA). We make use of the fully spin-resolved static and dynamical many-body local field factors of the two-dimensional electron gas (2DEG) to improve the calculations of the particle-hole and plasmon-mediated contributions to the SCD. Also, we incorporate in our calculations the transverse thickness of the quantum well in which the 2DEG resides. In contrast to the conventional charge Coulomb drag, in the SCD the effect of layer thickness is significant even at relatively high temperature and densities. The final outcome of our study is that the enhancement of the spin drag caused by many-body local field effects largely compensates the reduction of the effect coming from the finite well thickness, restoring good agreement with the experimental observations by C.P. Weber et al., Nature 437 (2005) 1330.