Quasiparticle Approach Research Articles

Effect of anisotropy on the formation of heavy quarkonium bound states

We study the real part of the static potential of a heavy quark-antiquark system in an anisotropic plasma medium. We use a quasiparticle approach where the collective dynamics of the plasma constituents is described using hard-loop perturbation theory. The parton distribution function is characterized by a set of parameters that can accurately describe the anisotropy of the plasma produced in a heavy ion collision. We calculate the potential numerically in strongly anisotropic systems and study the angular dependence of the distortion of the potential relative to the isotropic one. We obtain an analytic expression for the real part of the heavy quark potential in the limit of weak anisotropy using a model that expresses the potential in terms of effective screening masses that depend on the anisotropy parameters and the orientation of the quark-antiquark pair. A one-dimensional potential is formulated in terms of angle averaged screening masses that incorporate the anisotropy of the medium into a radial coordinate. We solve the corresponding Schrödinger equation and show that the magnitude of the binding energy typically increases with anisotropy. Anisotropy can play an important role, especially in states with nonzero angular momentum. This means that the number of bound states that are formed could depend on specific characteristics of the anisotropy of the plasma. Our study suggests that plasma anisotropy plays an important role in the dynamics of heavy quarkonium and motivates further study. Published by the American Physical Society 2024

Excitonic properties and solar harvesting performance of Cs2ZnY2X2 as quasi-2D mixed-halide perovskites

Due to their low toxicity and high-temperature stability, lead-free quasi-2D metal halide perovskites (MHPs) are promising materials for optoelectronic applications. However, understanding their structural and optoelectronic properties, especially excitonic effects (electron-hole pair, e-h), is challenging due to their quantum well topology. We propose an efficient protocol for band gap correction of Cs2ZnX (X = Cl4, Br2Cl2, and I2Cl2) and Cs2PbI2Cl2 (used as a benchmark) quasi-2D MHPs. This protocol is based on a relativistic quasiparticle approach (DFT-1/2) using density functional theory (DFT). We first examined the hybrid contributions of the halide alloys, leading to excitonic characterization using the Bethe–Salpeter equation within the maximally localized Wannier functions tight-binding method. This method provides a cost-effective approach for describing e-h quasiparticle effects. Additionally, we analyzed the crystal structure, thermodynamic stability, and optoelectronic properties of the newly synthesized Zn-based systems, focusing on their structural stability mechanisms. We found a correlation between the allocation of Cs+ cations in the crystal structure and the formation of two distinct stabilization patterns, influenced by the radii of the metal (Zn or Pb) and halide components. The relativistic correction of the band gap energies yielded results within 10 % of the experimental values. Furthermore, incorporating e-h quasiparticle effects for Cs2PbI2Cl2 resulted in an exciton binding energy of 0.160 eV, in excellent agreement with experimental data. This work represents a significant advance in the optoelectronic characterization of Cs2ZnX systems, previously unexplored for their excitonic properties.

Bexcitonics: Quasiparticle approach to open quantum dynamics.

We develop a quasiparticle approach to capture the dynamics of open quantum systems coupled to bosonic thermal baths of arbitrary complexity based on the Hierarchical Equations of Motion (HEOM). This is done by generalizing the HEOM dynamics and mapping it into that of the system in interaction with a few bosonic fictitious quasiparticles that we call bexcitons. Bexcitons arise from a decomposition of the bath correlation function into discrete features. Specifically, bexciton creation and annihilation couple the auxiliary density matrices in the HEOM. The approach provides a systematic strategy to construct exact quantum master equations that include the system-bath coupling to all orders even for non-Markovian environments. Specifically, by introducing different metrics and representations for the bexcitons it is possible to straightforwardly generate different variants of the HEOM, demonstrating that all these variants share a common underlying quasiparticle picture. Bexcitonic properties, while unphysical, offer a coarse-grained view of the correlated system-bath dynamics and its numerical convergence. For instance, we use it to analyze the instability of the HEOM when the bath is composed of underdamped oscillators and show that it leads to the creation of highly excited bexcitons. The bexcitonic picture can also be used to develop more efficient approaches to propagate the HEOM. As an example, we use the particle-like nature of the bexcitons to introduce mode-combination of bexcitons in both number and coordinate representation that uses the multi-configuration time-dependent Hartree to efficiently propagate the HEOM dynamics.

Dissociation of J/ψ and Y Using Dissociation Energy Criteria in N-Dimensional Space

The analytical exact iteration method (AEIM) has been widely used to calculate N-dimensional radial Schrodinger equation with medium-modified form of Cornell potential and is generalized to the finite value of magnetic field (eB) with quasiparticle approach in hot quantum chromodynamics (QCD) medium. In N-dimensional space, the energy eigenvalues have been calculated for any states (n, l). These results have been used to study the properties of quarkonium states (i.e, the binding energy and mass spectra, dissociation temperature, and thermodynamical properties in the N-dimensional space). We have determined the binding energy of the ground states of quarkonium with magnetic field and dimensionality number. We have also determined the effects of magnetic field and dimensionality number on mass spectra for ground states of quarkonia. But the main result is quite noticeable for the values of dissociation temperature in terms of magnetic field and dimensionality number for ground states of quarkonia after using the criteria of dissociation energy. At last, we have also calculated the thermodynamical properties of QGP (i.e., pressure, energy density, and speed of sound) using the parameter eB with ideal equation of states (EoS). A preprint has previously been published (Solanki et al., 2023).

A unified quasiparticle approach to the theory of strongly correlated electron liquids

Landau’s quasiparticle formalism is generalized to describe a wide class of strongly correlated Fermi systems, in addition to conventional Fermi liquids. This class includes (i) so-called marginal exemplars and (ii) systems that harbor interaction-driven flat bands, in both of which manifestations of non-Fermi-liquid behavior are well documented. Specifically, the advent of such flat bands is attributed to a spontaneous topological rearrangement of the Landau state that supplements the conventional Landau quasiparticle picture with a different set of quasiparticles, the so-called fermion condensate, whose single-particle spectrum is dispersionless. The celebrated Landau–Luttinger theorem is extended to marginal Fermi liquids, in which the density of the augmented quasiparticle system is shown to coincide with the particle density. On the other hand, the total density of a system hosting an interaction-driven flat band turns out to be the sum of the densities of the two quasiparticle subsystems: the Landau-like component and the fermion condensate. We demonstrate that within the framework of the scenario proposed, a long-standing problem faced by theories of D-wave superconductivity in cuprates, namely a consistent explanation of the so-called Uemera plot, can be naturally resolved.

Quasiparticle approach to collective quantum dielectric response

In current research, we use a generalized quantum multistream model to develop an effective quasiparticle theory for quantum many-body effects. The N-electron Schrödinger–Poisson stream model is reduced to a system of coupled differential equations with new wavefunction representation for collective quantum excitations in the many electron system. The current theory is then applied to the collective quantum statistical behavior of homogenous electron gas. Moreover, the generalized energy dispersion relation, which incorporates the quasiparticle band structure, is used to calculate the linear dielectric response of collective quantum excitations in the electron gas with arbitrary degree of degeneracy beyond many-body theories, limiting assumptions such as the independent electron and the random phase approximations. Important parameters of electron gas such as the dynamic structure factor, the loss function, the static charge screening, optical reflectivity, and the electronic stopping power are investigated as applications of current theory. The quasiparticle theory incorporates effects both due to single-electron excitations as well as the electrostatic interaction among electrons in a single picture. Existence of Van-Hove-like singularity at the plasmon wavenumber leads to distinct features of quasiparticle response to electromagnetic perturbations in the electron gas. It is shown that collective quantum excitations in high density electron gas below a given critical electron temperature are blocked due to existence of a large quasiparticle energy bandgap above the Fermi level. A new equation of states is given for the quasiparticle excitation in the electron gas, based on the transition probability of electrons to the quasiparticle level. It is found that, the screening potential of a static charge in quasiparticle model has an oscillatory Lennard–Jones-type attractive form.

Quasiparticle approach to the transport in infinite-layer nickelates

The normal-state transport properties of superconducting infinite-layer nickelates are investigated within an interacting three-orbital model. It includes effective Ni-${d}_{{z}^{2}}$ and Ni-${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ bands as well as the self-doping band degree of freedom. The thermopower, Hall coefficient, and optical conductivity are modeled within a quasiparticle approximation to the electronic states. Qualitative agreement in comparison to experimentally available Hall data is achieved, with notably a temperature-dependent sign change of the Hall coefficient for larger hole doping $x$. The Seebeck coefficient changes from negative to positive in a nontrivial way with $x$, but generally shows only a modest temperature dependence. The optical conductivity shows a pronounced Drude response and a prominent peak structure at higher frequencies due to interband transitions. While the quasiparticle picture is surely approximative to low-valence nickelates, it provides enlightening insights into the multiorbital nature of these challenging systems.

Fate of the upper polariton: Breakdown of the quasiparticle picture in the continuum

Organic polaritons resulting from the strong hybridisation between photons and matter excitations have arisen as a suitable platform to device light-matter technological interfaces at room temperature. Despite their inherent complexity, organic polaritons are commonly regarded as coherent light-matter excitations that can be described in terms of Landau's quasiparticle approach. Here, we experimentally unveil the role of incoherent matter excitations on the polaritons by exploring the relevant energy-momentum parameter space. We demonstrate the emergence of a well-defined lower polariton branch and an intriguing fading of the upper polariton at its entrance to a continuum of matter excitations. This marks the breakdown of the simplistic quasiparticle picture for this branch and the formation of a more complex quantum state. Our experimental results are sustained by a general theoretical framework that allows understanding the light-matter hybridisation beyond the quasiparticle approach. Our work expands the understanding of organic polaritons in all their complexity and increases their technological significance.

Gross theory of β decay by considering the spin-orbit splitting from relativistic Hartree-Bogoliubov theory

Nuclear $\ensuremath{\beta}$-decay half-lives are predicted with the so-called gross theory, which is improved by including the spin-orbit splitting from relativistic Hartree-Bogoliubov theory. The calculated differences between the Gamow-Teller and Fermi transition energies are in excellent agreement with experimental data for Zr, Sn, and Pb isotopes. The influences of the $Q$ value and the integrated Fermi function on the calculations of $\ensuremath{\beta}$-decay half-lives are carefully studied. Based on the mass predictions of the latest Weizs\"acker-Skyrme model, the half-lives from Ca to Pb isotopes are systematically calculated. It is found that the Weizs\"acker-Skyrme model well reproduces the experimental data with accuracy better than that of quasiparticle random-phase approximation approaches. When extrapolated to the unknown region, our results are generally close to those from the Skyrme finite-amplitude method. This improved gross theory can be employed to calculate half-lives based on mass predictions of various models and hence can provide relatively consistent half-life inputs for the $r$-process studies.

Effects of triaxiality and residual np interaction in the proton emission from Ho140

We present a detailed theoretical investigation of proton emission from $^{140}\mathrm{Ho}$ within the nonadiabatic quasiparticle approach. The calculated proton emission half-life reproduces well the measured data. The importance of triaxiality and of the residual $np$ interaction are studied. The ground state spin and parity of $^{139}\mathrm{Dy}$ (daughter) and $^{140}\mathrm{Ho}$ (parent) are ascertained unambiguously as $7/{2}^{+}$ and ${3}^{\ensuremath{-}}$, respectively, by analyzing the rotational energies, half-lives, and branching ratios.

Topological and quantum stability of low-dimensional crystalline lattices with multiple nonequivalent sublattices* *Dedicated to the memory of our close friend, fellow colleague, former student (PA) and teacher (AK) Prof. A A Kuzubov (1974–2016).

The terms of topological and quantum stabilities of low-dimensional crystalline carbon lattices with multiple non-equivalent sublattices are coined using theoretical analysis, multilevel simulations, and available experimental structural data. It is demonstrated that complex low-dimensional lattices are prone to periodicity breakdown caused by structural deformations generated by linear periodic boundary conditions (PBC). To impose PBC mandatory limitations for complex low-dimensional lattices, the topology conservation theorem (TCT) is introduced, formulated and proved. It is shown that the lack of perfect filling of planar 2D crystalline space by structural units may cause the formation of (i) structure waves of either variable or constant wavelength; (ii) nanotubes or rolls; (iii) saddle structures; (iv) aperiodic ensembles of irregular asymmetric atomic clusters. In some cases the lattice can be stabilized by aromatic resonance, correlation effects, or van-der-Waals interactions. The effect of quantum instability and periodicity breakdown of infinite structural waves is studied using quasiparticle approach. It is found that both perfect finite-sized, or stabilized structural waves can exist and can be synthesized. It is shown that for low-dimensional lattices prone to breakdown of translation invariance (TI), complete active space of normal coordinates cannot be reduced to a subspace of TI normal coordinates. As a result, constrained TI subspace structural minimization may artificially return a regular point at the potential energy surface as either a global/local minimum/maximum. It is proved that for such lattices, phonon dispersion cannot be used as solid and final proof of either stability or metastability. It is shown that ab initio molecular dynamics (MD) PBC Nosé–Hoover thermostat algorithm constrains the linear dimensions of the periodic slabs in MD box preventing their thermostated equilibration. Based on rigorous TCT analysis, a flowchart algorithm for structural analysis of low-dimensional crystals is proposed and proved to be a powerful tool for theoretical design of advanced complex nanomaterials.

Event-shape engineering analysis of D meson in ultrarelativistic heavy-ion collisions

We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of an event-by-event transport approach. In our calculations the non-perturbative interaction between heavy quarks and light partons has been taken into account through a quasi-particle approach with thermal light quark masses tuned to reproduce lQCD thermodynamics. We found that the flow observables v_2 and v_3 of D mesons are comparable with the experimental measurements for Pb + Pb collisions at 5.02 TeV in different ranges of centrality selections. The results are analyzed with event-shape engineering technique. The comparison of the anisotropic flow coefficients v_n with experimental data show a quite good agreement with experimental data for different flow vector q_2 selections, which confirms the strong coupling between charm quarks and light quarks in the QCD matter. Furthermore, we present here a novel study of the event-by-event correlations between flow harmonics of D mesons and soft hadrons at LHC energy with the event-shape engineering technique that can put further constraints on heavy quark transport coefficients toward a solid comparison between the phenomenological determination and the lattice QCD calculations.

Quark gluon plasma in the early universe expansion with quasi-particle approach

To understand the behaviour of Quark Gluon Plasma (QGP) in the early stages of universe, a precise temporal evolution of different thermodynamic parameters is studied. Out of many indirect signatures used for the detection of QGP, we compute the Equation of State (EoS) by solving the Friedmann equations. A phenomenological model is used with the value of thermal dependent finite quark mass. The variation of temperature, as well as the energy density with respect to time, are provided which predicts a suitable transition temperature for the phase transition. These results can also be used to calculate other thermodynamic observables. The evolution of early universe and its related properties are thus important in the detection of QGP.

Anharmonic thermodynamic properties and phase boundary across the postperovskite transition in MgSiO3

To address the effects of lattice anharmonicity across the perovskite to post-perovskite transition in MgSiO$_3$, we conduct calculations using the phonon quasiparticle (PHQ) approach. The PHQ is based on \textit{ab initio} molecular dynamics and, in principle, captures full anharmonicity. Free energies in the thermodynamic limit ($N \rightarrow \infty$) are computed using temperature-dependent quasiparticle dispersions within the phonon gas model. Systematic results on anharmonic thermodynamic properties and phase boundary are reported. Both the local density approximation (LDA) and the generalized gradient approximation (GGA) calculations are performed to provide confident constraints on these properties. Anharmonic effects are demonstrated by comparing results with those obtained using the quasiharmonic approximation (QHA). The inadequacy of the QHA is indicated by its overestimation of thermal expansivity and thermodynamic Gr\"{u}neisen parameter and its converged isochoric heat capacity in the high-temperature limit. The PHQ phase boundary has a Clapeyron slope ($dP/dT$) that increases with temperature. This result contrasts with the nearly zero curvature of the QHA phase boundary. Anharmonicity bends the phase boundary to lower temperatures at high pressures. Implications for the double-crossing of the phase boundary by the mantle geotherm are discussed.

Melting of Quarkonia in strong magnetic field

In this paper, spectra of the quarkonium states has been studied using the conditions temperature, chemical potential and the magnetic field. Here our main focus is to study the effect of strong magnetic field on the quarkonium properties. The binding energies and the dissociation temperature for the ground and the first excited states of the charmonium and bottomonium in the presence of strong magnetic field at chemical potential μ = 500 MeV has been studied. Here we use quasiparticle(QP) Debye mass depending upon temperature, magnetic field and chemical potential obtained from the quasiparticle approach. The Debye mass strongly increases at different values of temperature and magnetic field. The binding energy decreases with increase in the temperature at different magnetic field eB=0.3, 0.5, and 0.7 GeV2 and also decreases with magnetic field at different at T=200,300 and 400 MeV for the J/ψ, Ψ’, ϒ, and ϒ’ states of the quarkonia. The dissociation temperature of the quarkonium states falls with the increasing values of the magnetic field at critical temperature Tc =197 MeV.

The Phonon Quasiparticle Approach for Anharmonic Properties of Solids

Knowledge of lattice anharmonicity is essential to elucidate distinctive thermal properties in crystalline solids. Yet, accurate ab initio investigations of lattice anharmonicity encounter difficulties owing to the cumbersome computations. Here we introduce the phonon quasiparticle approach and review its application to various materials. This method efficiently and reliably addresses lattice anharmonicity by combining ab initio molecular dynamics and lattice dynamics calculations. Thus, in principle, it accounts for full anharmonic effects and overcomes finite-size effects typical of ab initio molecular dynamics. The validity and effectiveness of the current approach are demonstrated in the computation of thermodynamic and heat transport properties of weakly and strongly anharmonic systems.

Thermoelectric transport coefficients of quark matter

A thermal gradient and/or a chemical potential gradient in a conducting medium can lead to an electric field, an effect known as thermoelectric effect or Seebeck effect. In the context of heavy-ion collisions, we estimate the thermoelectric transport coefficients for quark matter within the ambit of the Nambu–Jona Lasinio (NJL) model. We estimate the thermal conductivity, electrical conductivity, and the Seebeck coefficient of hot and dense quark matter. These coefficients are calculated using the relativistic Boltzmann transport equation within relaxation time approximation. The relaxation times for the quarks are estimated from the quark–quark and quark–antiquark scattering through meson exchange within the NJL model. As a comparison to the NJL model estimation of the Seebeck coefficient, we also estimate the Seebeck coefficient within a quasiparticle approach.

The Role of Strange Quasiquarks in Transport Properties of the QGP

We study the role of dynamical quarks in the transport properties of the deconfined hot medium utilizing the quasiparticle kinetic approach. The system is then composed of the quasiparticle excitations, whose interactions are encoded in their dynamical masses with temperature dependence specified by the effective coupling extracted from lattice QCD thermodynamics. Evaluating the temperature and flavor profiles of the shear and bulk viscosities, as well as the electrical conductivity we examine how different particle species, in particular strange quarks, modify the transport parameters of the deconfined matter.

Hadron production within a full transport approach with statistical hadronization mechanism at RHIC and LHC energies

We present for the first time results on final hadron production, with and without strangeness content, in Ultrarelativistic Heavy Ion Collisions at RHIC and LHC center of mass energies obtained combining a full 3+1D relativistic Boltzmann transport approach with a statistical hadronization mechanism. The non-perturbative interaction between quarks and gluons is described by means of a quasi-particle approach that permits to have an Equation of State close to lattice QCD. The resulting framework naturally includes both shear and bulk viscous effects. The 3+1D full transport evolution is converted to hadrons by mean of a realistic freeze-out hypersurface considering all known hadron resonances and by performing resonance decays. We present results on charged-hadron multiplicity, identified-particle spectra and identified-particle elliptic flow of π, K and p produced at RHIC and LHC energies for different centralities.

Extended quasiparticle approach to non-resonant and resonant X-ray emission spectroscopy.

The initial states of the secondary processes of X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) are highly excited eigenstates with a deep core hole after a X-ray photoelectron spectroscopy (XPS) process and a X-ray photoabsorption spectroscopy (XAS) process, respectively, so that the XES and RIXS calculation offers a good example of extended quasiparticle theory (EQPT) (K. Ohno, S. Ono and T. Isobe, J. Chem. Phys., 2017, 146, 084108) which is applicable to any initial exited eigenstate. We apply the standard one-shot GW + Bethe-Salpeter equation (BSE) approach in MBPT to this problem on the basis of EQPT and analyze XES and RIXS spectra for CH4, NH3, H2O, and CH3OH molecules. We also suggest a simpler approach only using the GW calculation without solving the BSE to compute the XES and RIXS energies, although it cannot give the spectral intensity. Moreover, according to extended Kohn-Sham theory (T. Nakashima, H. Raebiger and K. Ohno, Phys. Rev. B, 2021, 104, L201116), we give a justification and comment of applying the method relying on time-dependent density functional theory as well as the one-shot GW + BSE approach to this problem.