Dense Fermi Research Articles

Specific Heat of Electron Plasma Waves.

Collective modes in a plasma, like phonons in a solid, contribute to a material's equation of state and transport properties, but the long wavelengths of these modes are difficult to simulate with today's finite-size quantum simulation techniques. A simple Debye-type calculation of the specific heat of electron plasma waves is presented, yielding up to 0.05k/e^{-} for warm dense matter (WDM), where thermal and Fermi energies are near 1 Ry=13.6 eV. This overlooked energy reservoir is sufficient to explain reported compression differences between theoretical hydrogen models and shock experiments. Such an additional specific heat contribution refines our understanding of systems passing through the WDM regime, such as the convective threshold in low-mass main-sequence stars, white dwarf envelopes, and substellar objects; WDM x-ray scattering experiments; and the compression of inertial confinement fusion fuels.

Static properties of a warm dense uniform electron gas

We show how the static dielectric function and other static characteristics of dense warm charged Fermi liquids can be obtained exclusively from the system static structure factor. The non-perturbative self-consistent method of moments is employed to extend onto quantum fluids, a similar reduction stemming from the fluctuation-dissipation theorem and other exact relations for classical one-component plasmas. The results are compared to and complement the numerical data obtained recently by the path-integral Monte Carlo method. Alternative theoretical approaches are discussed and employed as well.

KdV acoustic structure with exchange-correlation potential in plasmas

The effect of the exchange-correlation potential (ECP) on the profile of dust-acoustic solitary waves (DASWs) in dusty plasma containing degenerate electrons and ions was investigated. The present study focuses on the linear and nonlinear long-wavelength dust-acoustic waves in non-relativistic plasmas. The linear acoustic waves are analyzed using the multi-fluid model, whereas the reductive perturbation theory is applied to derive a modified Korteweg-de Vries (KdV) equation for small- but finite-amplitude waves. The effects of dust concentration and the exchange-correlation potential were investigated. These parameters remarkably change the amplitude and the width of the solitary waves. The findings from this investigation may lead to further understanding of the characteristics of nonlinear electrostatic waves exciting in the dense Fermi gas which is present in metallic nano structures or in near-supernovae environment in the presence of massive charge defects.

Convergence of the hole-line expansion with modern nucleon-nucleon potentials

The accurate computation of nuclear matter properties, such as its binding energy, is still a challenge to nuclear theory, largely because the quark substructure of nucleons creates a strong repulsion at short distances that renders a straightforward perturbative calculation impossible. In this work, the authors study the Brueckner-Bethe-Goldstone expansion of dense Fermi systems in terms of hole-line contributions, of the associated Goldstone diagrams, to the binding energy of nuclear matter. They use various modern nucleon-nucleon potentials of high precision. In all cases the three-hole-line contributions are sufficiently small suggesting that the expansion converges. Yet, the empirical saturation properties of nuclear matter are not reproduced for any potential. This means that very strong nuclear three-body forces are required in order to achieve satisfactory saturation properties of nuclear matter, and that such forces are essential for all considered potentials.

Free Time Evolution of a Tracer Particle Coupled to a Fermi Gas in the High-Density Limit

The dynamics of a particle coupled to a dense and homogeneous ideal Fermi gas in two spatial dimensions is studied. We analyze the model for coupling parameter g=1 (i.e., not in the weak coupling regime), and prove closeness of the time evolution to an effective dynamics for large densities of the gas and for long time scales of the order of some power of the density. The effective dynamics is generated by the free Hamiltonian with a large but constant energy shift which is given at leading order by the spatially homogeneous mean field potential of the gas particles. Here, the mean field approximation turns out to be accurate although the fluctuations of the potential around its mean value can be arbitrarily large. Our result is in contrast to a dense bosonic gas in which the free motion of a tracer particle would be disturbed already on a very short time scale. The proof is based on the use of strong phase cancellations in the deviations of the microscopic dynamics from the mean field time evolution.

Way to observe the implausible “trion-polariton”

Using the composite boson (coboson) many-body formalism, we determine under which conditions “trion-polariton” can exist. Dipolar attraction can bind an exciton and an electron into a trion having an energy well separated from the exciton energy. Yet, the existence of long-lived “trion-polariton” is a priori implausible not only because the photon-trion coupling, which scales as the inverse of the sample volume, is vanishingly small, but mostly because this coupling is intrinsically “weak”. Here, we show that a moderately dense Fermi sea renders its observation possible: on the pro side, the Fermi sea overcomes the weak coupling by pinning the photon to its momentum through Pauli blocking; it also overcomes the dramatically poor photon-trion coupling by providing a volume-linear trion subspace to which the photon is coherently coupled. On the con side, the Fermi sea broadens the photon-trion resonance due to the fermionic nature of trions and electrons; it also weakens the trion binding by blocking electronic states relevant for trion formation. As a result, the proper way to observe this novel polariton is to use a doped semiconductor having long-lived electronic states, a highly bound trion and a Fermi energy as large as a fraction of the trion binding energy.

Accretion-caused deceleration of a gravitationally powerful compact stellar object moving within a dense Fermi gas

We consider accretion-caused deceleration of a gravitationally-powerful compact stellar object traveling within a cold Fermi-gas medium. We provide analytical and numerical estimates of the effect manifestation.

Obliquely propagating solitary structures in a heavier ion Fermi plasma

By employing quantum hydrodynamic formulation, oblique propagation of electrostatic ion waves and nonlinear structures are investigated in a magnetized dense Fermi plasma. Constituents are quantum (degenerate) electrons and non-degenerate mobile ions in presence of stationary massive ions (either positive or negative) in background. To reveal features of low frequency ion waves, where effects of Fermi degeneracy and quantum diffraction are significant, linear dispersion equation is derived by Fourier analysis of model equations. Nonlinear solitary pulse solution in low-amplitude limit is obtained via Korteweg de Vries equation. It is shown that wave dispersion due to electron Fermi pressure is important at very short wavelength regime. Effects of concentration of heavy ions and angle of propagation on wave are also studied. Results are discussed numerically with relevance of superdense plasmas mainly found in astrophysical regimes.

Phase diagram of a gauge theory with fermionic baryons

The fermion-sign problem at finite density is a persisting challenge for Monte-Carlo simulations. Theories that do not have a sign problem can provide valuable guidance and insight for physically more relevant ones that do. Replacing the gauge group SU(3) of QCD by the exceptional group G2, for example, leads to such a theory. It has mesons as well as bosonic and fermionic baryons, and shares many features with QCD. This makes the G2 gauge theory ideally suited to study general properties of dense, strongly-interacting matter, including baryonic and nuclear Fermi pressure effects. Here we present the first-ever results from lattice simulations of G2 QCD with dynamical fermions, providing a first explorative look at the phase diagram of this QCD-like theory at finite temperature and baryon chemical potential.

Thermal Gravitational Waves from Primordial Black Holes

Thermal gravitational waves can be generated in various sources such as, in the cores of stars, white dwarfs and neutron stars due to the fermion collisions in the dense degenerate Fermi gas. Such high frequency thermal gravitational waves can also be produced during the collisions in a gamma ray burst or during the final stages of the evaporation of primordial black holes. Here we estimate the thermal gravitational waves from primordial black holes and estimate the integrated energy of the gravitational wave emission over the entire volume of the universe and over Hubble time. We also estimate the gravitational wave flux from gamma ray bursts and jets.

Nonlinear saturation of the Weibel instability in a dense Fermi plasma

AbstractWe present an investigation for the generation of intense magnetic fields in dense plasmas with an anisotropic electron Fermi–Dirac distribution. For this purpose, we use a new linear dispersion relation for transverse waves in the Wigner–Maxwell dense quantum plasma system. Numerical analysis of the dispersion relation reveals the scaling of the growth rate as a function of the Fermi energy and the temperature anisotropy. The nonlinear saturation level of the magnetic fields is found through fully kinetic simulations, which indicates that the final amplitudes of the magnetic fields are proportional to the linear growth rate of the instability. The present results are important for understanding the origin of intense magnetic fields in dense Fermionic plasmas, such as those in the next-generation intense laser–solid density plasma experiments.

Electron acoustic solitary waves in unmagnetized two electron population dense plasmas

The electron acoustic solitary waves are studied in unmagnetized two population electron quantum plasmas. The quantum hydrodynamic model is employed with the Sagdeev potential approach to describe the arbitrary amplitude electron acoustic waves in a two electron population dense Fermi plasma. It is found that hot electron density hump structures are formed in the subsonic region in such type of quantum plasmas. The wave amplitude as well as the width of the soliton are increased with the increase of percentage presence of cold (thinly populated) electrons in a multicomponent quantum plasma. It is found that an increase in quantum diffraction parameter broadens the nonlinear structure. Furthermore, the amplitude of the nonlinear electron acoustic wave is found to increase with the decrease in Mach number. The numerical results are also presented to understand the formation of solitons in two electron population Fermi plasmas.

Bound states and superconductivity in dense Fermi systems

A quantum field theoretical approach to the thermodynamics of dense Fermi systems is developed for the description of the formation and dissolution of quantum condensates and bound states in dependence of temperature and density. As a model system we study the chiral and superconducting phase transitions in two-flavor quark matter within the NJL model and their interrelation with the formation of quark-antiquark and diquark bound states. The phase diagram of quark matter is evaluated as a function of the diquark coupling strength and a coexistence region of chiral symmetry breaking and color superconductivity is obtained at very strong coupling. The crossover between Bose-Einstein condensation (BEC) of diquark bound states and condensation of diquark resonances (Cooper pairs) in the continuum (BCS) is discussed as a Mott effect. This effect consists in the transition of bound states into the continuum of scattering states under the influence of compression and heating. We explain the physics of the Mott transition with special emphasis on role of the Pauli principle for the case of the pion in quark matter.

Equivalent charge of photons in a very dense quantum plasma

AbstractThe equivalent charge of photons in dense unmagnetized and magnetized Fermi plasmas is determined through the plasma physics method. This charge is associated with the polarization of the medium caused by the ponderomotive force of the electromagnetic waves. Relations for the coupling between the electron plasma density perturbation and the radiation fields are derived for unmagnetized and magnetized plasmas, taking into account the quantum force associated with the quantum Bohm potential in dense Fermi plasmas. The effective photon charge is then determined. The effects of the ion motion are also included in the investigation.

Ion-temperature-gradient driven modes in very dense magnetoplasmas

By employing the quantum magnetohydrodynamic-Poisson model, a general dispersion relation for low-frequency electrostatic ion-temperature-gradient (ITG) modes in a very dense Fermi plasma is derived. The growth rate is found to be higher in the presence of ion-temperature gradients and electron corrections due to quantum fluctuations. Two new ITG driven modes in the Fermi plasma are found. These ITG modes are associated with an electron density response that differs from the Boltzmann law. It is expected that newly found ITG modes can play an important role in anomalous cross-field ion energy transport in the next-generation laser-solid density plasma experiments as well as in dense astrophysical bodies (e.g., neutron stars and the interior of white dwarfs).

Nonlinear Theory for a Quantum Diode in a Dense Fermi Magnetoplasma

We present a simple analytical nonlinear theory for quantum diodes in a dense Fermi magnetoplasma. By using the steady-state quantum hydrodynamical equations for a dense Fermi magnetoplasma, we derive coupled nonlinear Schrödinger and Poisson equations. The latter are numerically solved to show the effects of the quantum statistical pressure, the quantum tunneling (or the quantum diffraction), and the external magnetic field strength on the potential and electron density profiles in a quantum diode at nanometer scales. It is found that the quantum statistical pressure introduces a lower bound on the steady electron flow in the quantum diode, while the quantum diffraction effect allows the electron tunneling at low flow speeds. The magnetic field acts as a barrier, and larger potentials are needed to drive currents through the quantum diode.

Arbitrary amplitude dust ion acoustic solitary waves in dense Fermi plasmas

The arbitrary amplitude dust ion acoustic solitary waves are investigated in unmagnetized quantum plasmas. The quantum hydrodynamic model is employed with the Sagdeev potential approach to describe the nonlinear dust ion acoustic waves in dense Fermi plasmas. It is found that electron density dip structures are formed in the subsonic as well as in the supersonic regions in such dense dusty plasmas. The range of wave Mach number is increased with the increase in the static dust density in quantum plasmas. Both the wave amplitude and width of the nonlinear structure are affected by static dust density. The quantum parameter effects only the width of the nonlinear structure. The amplitude of dust ion acoustic solitary wave is reduced with the increase in the wave Mach number.

Free Fermion limit of the strong-coupling Kondo lattice model

The strong-coupling Kondo lattice model is an interacting dense Fermi system for which conventional Fermi gas analysis has thus far failed. We will see that there exists, in fact, an exact transformation that maps the singlet Mott insulator to a Fermi vacuum and simultaneously maps bare c-electron and f-electron operators to Fermion electron and hole quasiparticles. For strong coupling, the quasiparticle dynamics are very simple. The complexity of describing the dynamics of the conventional electron operators in the singlet Mott insulator can be reduced to a complicated but precise relation between quasiparticle and bare electrons operators which exactly obey the electron spectral weight sum rules.

Neutrino effective charge in a dense Fermi plasma

By using a plasma physics approach, the neutrino effective charge in a dense Fermi plasma is determined here. Its value is determined by the collective quantum plasma processes. It is found that the contribution of the ion motion can be important even in Fermi plasmas, despite the negligible weak interaction between neutrinos and ions. This results from the electron–ion couplings, which are dominant in the low-frequency limit of the equivalent charge spectrum.

Strong coupling Kondo lattice model as a Fermi gas

The strong coupling half-filled Kondo lattice model is an important example of a strongly interacting dense Fermi system for which conventional Fermi gas analysis has thus far failed. We remedy this by deriving an exact transformation that maps the model to a dilute gas of weakly interacting electron and hole quasiparticles that can then be analyzed by conventional dilute Fermi gas methods. The quasiparticle vacuum is a singlet Mott insulator for which the quasiparticle dynamics are simple. Since the transformation is exact, the electron spectral weight sum rules are obeyed exactly. Subtleties in understanding the behavior of electrons in the singlet Mott insulator can be reduced to a fairly complicated but precise relation between quasiparticles and bare electrons. The theory of free quasiparticles can be interpreted as an exactly solvable model for a singlet Mott insulator, providing an exact model in which to explore the strong coupling regime of a singlet Kondo insulator.