Collective Plasma Modes Research Articles

Collective modes of plasma formed by multiphoton ionization of rarefied gas

High-frequency collective modes in plasma with strongly anisotropic velocity distribution of photoelectrons formed by multiphoton or above-threshold ionization of gas atoms are studied. In the case of multiphoton ionization, along with the usual electromagnetic wave, there are two additional modes. In the region of large wavelengths, the higher-frequency mode is similar to the electron Langmuir wave. Its group velocity is mainly determined by the average photoelectron velocity, and Cherenkov damping is due to small velocity dispersion of photoelectron distribution. In the region of short waves, but with a small Cherenkov damping, the group and phase velocities of this wave are close to the average electron velocity. The second mode, which has lower frequency, in the region of wavelengths smaller than the ratio of average electron velocity to the plasma frequency, corresponds to quasi-potential wave. Its dispersion law is close to the linear one. In contrast, in the region of large wavelengths, this mode corresponds to aperiodic instability, the maximum growth rate of which is comparable to the plasma frequency. The distribution of photoelectrons formed during above-threshold ionization is characterized by the large number of energy peaks, which is accompanied by increasing in the number of collective modes. In particular, in plasma with photoelectron distribution which has two energy peaks, in addition to the electromagnetic mode four extra modes are possible. In the shortwave region, all four modes correspond to the waves that are damped due to Cherenkov interaction with photoelectrons. Two of these modes in the region of relatively long wavelengths are unstable. One of these unstable modes corresponds to quasi-potential wave whose amplitude aperiodically increases with time. The reason for the instabilities is the presence of counter streams of photoelectrons.

Pairing from dynamically screened Coulomb repulsion in bismuth

Recently, Prakash et. al. have discovered bulk superconductivity in single crystals of bismuth, which is a semi metal with extremely low carrier density. At such low density, we argue that conventional electron-phonon coupling is too weak to be responsible for the binding of electrons into Cooper pairs. We study a dynamically screened Coulomb interaction with effective attraction generated on the scale of the collective plasma modes. We model the electronic states in bismuth to include three Dirac pockets with high velocity and one hole pocket with a significantly smaller velocity. We find a weak coupling instability, which is greatly enhanced by the presence of the hole pocket. Therefore, we argue that bismuth is the first material to exhibit superconductivity driven by retardation effects of Coulomb repulsion alone. By using realistic parameters for bismuth we find that the acoustic plasma mode does not play the central role in pairing. We also discuss a matrix element effect, resulting from the Dirac nature of the conduction band, which may affect $T_c$ in the $s$-wave channel without breaking time-reversal symmetry.

Quantum well electron scattering rates through longitudinal optic-phonon dynamical screened interaction: An analytic approach

A quantum model is developed to obtain electron capture and hot electron intraband relaxation times in a quantum well, for electron-longitudinal optic (LO) phonon scattering. In particular, we have investigated the effect of carrier density and electron energy, obtaining semi-analytic expressions as function of carrier density, a topic often neglected in literature, despite its fundamental interest in semiconductor physics. We demonstrated that the usual approximation of constant scattering time in modeling applications is often not adequate, because these parameters vary considerably with the injected or photogenerated carrier density. Furthermore we show that the scattering through the emission of pure LO-phonons is not a good approximation when the population increases, whereas the interplay between LO-phonon and collective plasma modes must be considered. We obtained novel semi-analytic expressions in the single plasmon pole dynamical form of the random phase approximation, without making use of the more usual static limit of it.

Aspects of the theory of graphene

Following a brief review of the device-friendly features of graphene, recent work on its Green's functions with and without a normal magnetic field are discussed, for an infinite graphene sheet and also for a quantum dot, with analyses of the Landau-quantized energy spectra of the sheet and dot. The random phase approximation dielectric response of graphene is reviewed and discussed in connection with the van der Waals interactions of a graphene sheet with atoms/molecules and with a second graphene sheet in a double layer. Energy-loss spectroscopy for a graphene sheet subject to both parallel and perpendicular particle probes of its dynamic, non-local response properties are also treated. Furthermore, we discuss recent work on the coupling of a graphene plasmon and a surface plasmon, yielding a collective plasma mode that is linear in wavenumber. Finally, we discuss the unusual aspects of graphene conduction and recent work on diffusive charge transport in graphene, in both the DC and AC regimes.

Electronic, optical and thermal excitation of plasma waves in HEMTs: A theoretical study

We investigate the influence of collective plasma modes in a field-effect transistor channel under different excitations and biasing conditions. First, we study the case of a device externally-excited by a harmonic optical beating or an electronic excitation and current-driven at the drain. The harmonic and continuous responses of the transistor are calculated using a pseudo-two-dimensional hydrodynamic approach. They show sharp resonances related to the first odd plasma modes, whose frequencies and amplitudes can be modified by playing on the drain bias. Then, through the generalized impedance-field method we calculate also the spectral density of drain voltage fluctuations in the absence of external excitations. Also these noise spectra exhibit peaks corresponding to the odd plasma modes.

Plasmon excitations in homogeneous neutron-star matter

We study the possible collective plasma modes which can affect neutron-star thermodynamics and different elementary processes in the baryonic density range between nuclear saturation ρ 0 and 3ρ 0. In this region, the expected constituents of neutron-star matter are mainly neutrons, protons, electrons, and muons (npeµ matter), under the constraint of beta equilibrium. The elementary plasma excitations of the peµ three-fluid medium are studied in the RPA framework. We emphasize the relevance of the Coulomb interaction among the three species, in particular, the interplay of the electron and muon screening in suppressing the possible proton plasma mode, which is converted into a sound-like mode. The Coulomb interaction alone is able to produce a variety of excitation branches and the full spectral function shows a rich structure at different energy. The genuine plasmon mode is pushed at high energy and it contains mainly an electron component with a substantial muon component, which increases with density. The plasmon is undamped for not too large momentum and is expected to be hardly affected by the nuclear interaction. All the other branches, which fall below the plasmon, are damped or over-damped.

Colloquium: Field theoretic description of ultrarelativistic electron-positron plasmas

Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.

Ultrarelativistic electron-positron plasma

Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.

Single-particle spectral function for the classical one-component plasma

The spectral function for an electron one-component plasma is calculated self-consistently using the GW;{(0)} approximation for the single-particle self-energy. In this way, correlation effects that go beyond the mean-field description of the plasma are contained, i.e., the collisional damping of single-particle states, the dynamical screening of the interaction, and the appearance of collective plasma modes. Second, a nonperturbative analytic solution for the on-shell GW;{(0)} self-energy as a function of momentum is presented. It reproduces the numerical data for the spectral function with a relative error of less than 10% in the regime where the Debye screening parameter is smaller than the inverse Bohr radius, kappa<1a_{B};{-1} . In the limit of low density, the nonperturbative self-energy behaves as n;{14} , whereas a perturbation expansion leads to the unphysical result of a density-independent self-energy [Fennel and Wilfer, Ann. Phys. (Leipzig) 32, 265 (1974)]. The derived expression will greatly facilitate the calculation of observables in correlated plasmas (transport properties, equation of state) that need the spectral function as an input quantity. This is demonstrated for the shift of the chemical potential, which is computed from the analytical formulas and compared to the GW;{(0)} result. At a plasma temperature of 100eV and densities below 10;{21}cm;{-3} , the two approaches deviate by less than 10% from each other.

Self-consistent spectral function for non-degenerate Coulomb systems and analytic scaling behaviour

Novel results for the self-consistent single-particle spectral function and self-energy are presented for non-degenerate one-component Coulomb systems at various densities and temperatures. The GW(0)-method for the dynamical self-energy is used to include many-particle correlations beyond the quasi-particle approximation. The self-energy is analysed over a broad range of densities and temperatures (n = 1017 cm−3–1027 cm−3, T = 102 eV/kB–104 eV/kB). The spectral function shows a systematic behaviour, which is determined by collective plasma modes at small wavenumbers and converges towards a quasi-particle resonance at higher wavenumbers. In the low density limit, the numerical results comply with an analytic scaling law that is presented for the first time. It predicts a power-law behaviour of the imaginary part of the self-energy, ImΣ ∝ −n1/4. This resolves a long time problem of the quasi-particle approximation which yields a finite self-energy at vanishing density.

Collective modes of ultra-relativistic magnetoactive electron plasma

Collective modes of ultra-relativistic electron plasma embedded in an ambient weak magnetic field are derived. Employing Maxwell equations in the four-dimensional Minkowski space and using the Vlasov model, polarization tensor is calculated and dispersion relations are obtained for both parallel and perpendicular propagations in the temporal axial gauge. Some interesting limiting cases are also discussed.

Collective Josephson vortex dynamics in a finite number of stacked intrinsic Josephson junctions

We report the experimental confirmation of the collective transverse plasma modes excited by the Josephson vortex lattice in stacks of intrinsic Josephson junctions in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ single crystals. The excitation was confirmed by analyzing the temperature ($T$) and magnetic field ($H$) dependencies of the multiple sub-branches in the Josephson-vortex-flow region of the current-voltage characteristics of the system. In the near-static Josephson vortex state for a low tunneling bias current, pronounced magnetoresistance oscillations were observed, which represented a triangular-lattice vortex configuration along the c axis. In the dynamic vortex state in a sufficiently high magnetic field and for a high bias current, splitting of a single Josephson vortex-flow branch into multiple sub-branches was observed. Detailed examination of the sub-branches for varying $H$ field reveals that sub-branches represent the different modes of the Josephson-vortex lattice along the c axis, with varied configuration from a triangular to a rectangular lattices. These multiple sub-branches merge to a single curve at a characteristic temperature, above which no dynamical structural transitions of the Josephson vortex lattice is expected.

Microwave generation by Josephson vortex motion in stacked high- Tc intrinsic junctions

We report the observation of the collective transverse plasma (CTP) modes induced by the Josephson vortex lattice motion and the excitation of corresponding electromagnetic waves in a stack of intrinsic Josephson junctions (IJJs) in Bi 2Sr 2CaCu 2O 8+ x . The existence of the CTP modes was confirmed by observing the sub-branches in the tunneling current–voltage curves of staked junctions in the Josephson vortex-flow region. For a proper bias in the sub-branches, the emission of the electromagnetic waves by the collective vortex resonance motion in a stack of IJJs (the oscillator stack) was examined using another on-chip stack of IJJs (the detector stack). The microwave emission from the oscillator stack and the resulting irradiation onto the detector stack was evidenced by the increase of Josephson vortex-flow voltages in the detector stack.

Thomson scattering from near-solid density plasmas using soft X-ray free electron lasers

We discuss a collective Thomson scattering experiment at the VUV free electron laser facility at DESY (FLASH) to diagnose warm dense matter at near-solid density. The plasma region of interest marks the transition from an ideal plasma to a correlated and degenerate many-particle system and is of current interest, e.g., in ICF experiments or laboratory astrophysics. Plasma diagnosis of such plasmas is a longstanding issue which is addressed here using a pump–probe scattering experiment to reveal the collective electron plasma mode (plasmon) using the high-brilliance radiation to probe the plasma. Distinctive scattering features allow one to infer basic plasma properties. For plasmas in thermal equilibrium the electron density and temperature are determined from scattering off the plasmon mode.

Vortex-flow electromagnetic emission in stacked intrinsic Josephson junctions

We confirmed the existence of the collective transverse plasma modes excited by the motion of the Josephson vortex lattice in stacked intrinsic Josephson junctions of Bi2Sr2CaCu2O8+x by observing the multiple subbranches in the Josephson-vortex-flow current-voltage characteristics. We also observed the symptom of the microwave emission from the resonance between the Josephson vortex lattice and the collective transverse plasma modes, which provides the possibility of developing Josephson-vortex-flow electromagnetic oscillators.

Progress in THz Generation Using Josephson Fluxon Dynamics in Intrinsic Junctions

Collective transverse plasma modes in Bi 2 Sr 2 CaCu 2 O 8+x intrinsic Josephson junctions (UJs) can be excited by the moving fluxon lattices. Progressive transformation of the standing-wave-like fluxon-lattice configuration from a triangular lattice to a rectangular lattice takes place as the dynamic fluxon-lattice modes are in resonance with the collective transverse plasma modes. In this paper, we review the progress in terahertz-frequency-range electromagnetic wave generation from the IJJs using the resonance between moving fluxon lattice and the collective transverse plasma modes.

Plasma modes in low-dimensional electron system over surface of liquid helium

The collective plasma modes in a quasi-two-dimensional (Q2D) electron system located over the free surface of liquid helium are studied theoretically within many-body dielectric formalism. The dispersion of modes is considered both over bulk liquid and over helium film where the essential modification of interelectron interaction occurs due to screening effects in the substrate with a large value of dielectric constant. It is shown that the plasma spectrum consists of longitudinal and transverse branches which dispersion laws depend on the values of the dielectric constant of helium and the film thickness. For the helium film covering metal, the longitudinal mode is acoustic differing of that for the surface electron (SE) system over bulk helium.

1D and 2D STLS dielectric functions for carriers in the lowest subband

AbstractWhen electrons or holes in 1D (quantum wires) and 2D (quantum layers) systems are confined in the lowest subband by transverse harmonic potentials, it is possible to find useful analytical expression for some important physical properties, such as the 1D and 2D effective interparticle Coulomb potentials, their Fourier transforms and their STLS dielectric functions with the corresponding collective plasma modes. Finite thickness effects of the confinement potentials can be easily identified and expanded in all formulae for carriers in the lowest subband. Finite thickness effects are much more pronounced in 1D than in 2D. We also calculate broadening effects with the Mermin correction of STLS. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Dielectric response function and stopping power of dense magnetized plasma

Using a kinetic-theoretic approach to Fokker–Planck equilibrium of thermonuclear α particles in dense and magnetized plasmas, the corresponding longitudinal dielectric function is investigated at length. It is used to evaluate the energy loss of the αs′ through the excitation of collective plasma modes. Specific attention was paid to the case of extreme magnetization, as well as to the parallel stopping of α particles in dense and hot plasmas of magnetized target fusion (MTF) interest. Maximum stopping is shown to be strongly dependent on magnetic field intensity.

Dynamical Breaking of Charge Neutrality in Intrinsic Josephson Junctions: Common Origin for Microwave Resonant Absorptions and Multiple-Branch Structures in theI−VCharacteristics

We demonstrate that both microwave resonant absorptions and multiple-branch structures in the $I\ensuremath{-}V$ characteristics observed in intrinsic Josephson junctions are caused by the dynamical breaking of the charge neutrality inside the atomic-scale superconducting layers. The Lagrangian for the time-dependent Lawrence-Doniach model incorporating the charge neutrality breaking effect is proposed. On the basis of the Lagrangian, the longitudinal collective Josephson plasma mode is proved to exist. The branching behaviors in the $I\ensuremath{-}V$ curves are almost completely reproduced by careful numerical simulations for the model equation derived from the Lagrangian.