Electron Gas In Quantum Research Articles

Effect of plasmon excitations in relativistic quantum electron gas

In this research, we use the generalized quantum multistream model to describe collective qusiparticle excitations in electron gas with arbitrary degree of degeneracy and relativity. The effective Schrödinger–Poisson and square-root Klein–Gordon–Poisson models are applied to study the energy band structure and statistical parameters of finite temperature quantum and relativistic quantum electron gas in neutralizing background charge. Based on the plasmon energy bandgap appearing above the Fermi level, a new equation of state for quasiparticle (collective) excitations with new plasma parameter definition is suggested for dense plasmas applicable to a wide range of electron temperature and density. The new criterion for quasiparticle excitations reveals some interesting aspects of relativistic quantum matter at extreme condition, such as the plasmon blackout and collective quantum pressure collapse, which are studied in the frameworks of both non-relativistic and relativistic quantum phenomena. Current quasiparticle model predicts density-temperature regimes in warm-dense matter for which collective excitations become ineffective. On the other hand, the energy band structure model predicts the quasiparticle pressure collapse in temperature–density regime close to that of white dwarf stars. The energy band structure is a powerful concept in condensed matter physics and is shown to have applications for collective quantum excitations in electron gas. It can also have direct applications in quasiparticle dielectric response and thermodynamic properties of electron gas in inertial confinement fusion, stellar core, compact stars, and charged relativistic quantum environments. It is interesting that the basic thermodynamic behavior of non-relativistic and relativistic quantum electron gases closely match up to temperature and number density of typical white dwarfs where the gravitational collapse is prone to occur. This evidently confirms the relevance of non-relativistic quantum plasmon model to study the collective excitations in warm dense matter and white dwarfs.

On the potential variation of charged dust in Saturn's magnetosphere: The dust-plasma interaction

We presented a theory describing interaction between cold plasma and dust grain based on Cassini observations of Enceladus in Saturn's E ring. We assumed a finite-sized dust cloud with inside plasma to simulate the environment. The dust cloud that results from this scenario has a different potential than the surrounding plasma. Cassini's observations revealed the cold plasma characteristics of the Enceladus plume, which include a high plasma density for both electrons and ions at sufficient low temperature. Therefore, the electron fluid is incorporated in the cloud to form a quantum electron gas governed through Fermi-Dirac statistics. According to observations, more electrons bound to the dust grain results in a collective dust plasma interaction with surrounding cold plasma. Dust-plasma interaction predominantly occurred at negative sub-micrometer sized dust grain. • Using Cassini observations of Enceladus in Saturn's E ring as a groundwork, a theory is presented in this article. • The Enceladus plume has cold plasma characteristics. We considered ions as Boltzmannian distributed particles and Fermi-Dirac distribution is applicable for electrons. • We derived relations for the potential variation in the Enceladus plume region and the E-rings. We found that more electrons bound to the dust grain results in a collective dust plasma interaction. • Analytical analysis and the numerical results form the expressions for the given environment is presented.

Stopping Power Modulation by Pump Waves of Charged Particles Moving above Two-Dimensional Electron Gases

The perturbation electron density and stopping power caused by the movement of charged particles above two-dimensional quantum electron gases (2DQEG) have been studied in numerous works using the quantum hydrodynamic (QHD) theory. In this paper, the QHD is modified by introducing the two-dimensional electron exchange-correlation potential at high density Vxc2DH and the pump wave modulations. Based on the modified QHD, the perturbation electron density and stopping power are calculated for pump waves with various parameters. The results show that the stopping power values are more accurate after considering Vxc2DH. Under the modulation of pump waves with the wavelength from 0.1nm to 0.1cm, the perturbation electron density of 2DQEG and the stopping power of charged particles show periodic changes. Under the modulation of pump waves with λ = 1.76 × 10−4 cm and Φ0=2×1010e/λf, the average stopping power with respect to the time phase θ becomes negative, which means that the charged particles will gain energy and can be accelerated. This is a new phenomenon in the fields of 2DQEG and of great significance in surface physics and surface modification in nanoelectronic devices with beam matter interactions.

Quantum interference of three dimensional plasmon excitations

In this paper, the quantum interference of plasmon excitations in the presence of charges or multipolar sources/sinks is investigated. The effective Schrödinger-Poisson system for dynamical description of the arbitrary degenerate fermi gas is reduced to a set of coupled linear pseudoforce system, and it is shown that this system admits a general multipolar solution in the 3D Cartesian coordinate. The obtained solution is then used to study well-known problems such as the double and quadruple charge interference effects. The double source interference produces patterns quite reminiscent of that of the double slit interference with the corresponding matter-wavelength matching that of the de Broglie wavelength of the electrons. It is found that the collective electrostatic interactions of quantum electron gas leads to the electrostatic energy depletion around the pole which causes electrostatic polar binding in the electron fluid. The later effect which has also been previously reported in some research seems to be an appropriate description of attractive metallic bindings. The current model is then extended to electronic interference effects in a crystal lattice with the quasiperiodic electronic states. The periodic arrangement of ionic cores in a crystal is shown to produce different density and electrostatic potential patterns for given energy eigenvalues of the fermi gas. Moreover, a generalized expression is obtained for electron probability current in the Schrödinger-Poisson model. The current model may provide a better platform for studying the quantum interference phenomenon in complex environments such as nanocompounds and plasmonic crystals.

Quantized plasmon excitations of electron gas in potential well

Using the Schrödinger-Poisson system in this paper, the basic quantum features of plasmon excitations in a free noninteracting electron gas with arbitrary degeneracy are investigated. The standing wave solution of the free electron gas is derived from the corresponding linearized pseudo-force system with appropriate boundary conditions. It is shown that the plasmon excitation energies for electron gas confined in an infinite potential well are quantized eigenvalues of which are obtained. It is found that any arbitrary degenerate quantum electron gas possesses two different characteristic length scales, unlike the classical dilute electron gas, with the smaller length scale corresponding to the single particle oscillation and the larger one due to the collective Langmuir excitations. The probability density of the free electron gas in a box contains fine structures which are modulated over a larger pattern. The envelope probability density profile for the electron Fermi gas confined in an impenetrable well in different energy states is found to be quite similar to that of the free electron confined to an infinite potential well. However, the illustrative features of the plasmon theory presented in this research can be further elaborated in order to illuminate a wide range of interesting physical phenomena involving both the single particle and the collective features.

Finite-temperature correlations in a two-dimensional electron gas within a dynamical self-consistent mean-field approximation

We have studied the effect of temperature on density-density correlations in a two-dimensional quantum electron gas by using the dynamical Singwi-Tosi-Land-Sjölander (STLS) theory. Static correlation functions viz. structure factor S(q; T), pair-correlation function g(r; T), and static density susceptibility χ(q, 0; T) are calculated over a wide range of temperature and electron density. The inclusion of the dynamics of correlations is found to cause a strong peak in S(q; T) at q ∼ 2.5kF for low densities. Correspondingly, there develops a sharp peak in χ(q, 0; T) that diverges below a critical density. This divergence is interpreted as a precursor of transition to finite-temperature Wigner crystal state. Rise in temperature tends to oppose the crystallization, with critical transition density decreasing with temperature. It is rather found that the dynamical correction to the conventional (static) STLS theory becomes small at a sufficiently high temperature. We have also calculated the plasmon dispersion for the GaAs quantum well based electron system and found that, except at ultra-low densities, agreement with the experimental data of Hirjibehedin et al. is reasonably good. Our results show a red shift in plasmon frequency over the predictions of the STLS and dynamical Hubbard approaches.

Dynamical screening function and plasmons in the wide HgTe quantum wells at high temperatures

Dynamical screening function of the two-dimensional electron gas in wide HgTe quantum well (QW) has been numerically modelled in this work. Calculations were provided in the Random Phase Approximation (RPA) framework and were based on Lindhard equation. Our simulations directly incorporated non-parabolicity of bulk 2D carriers spectrum, which was obtained by full 8-band k.p method. In the literature exists data that transport properties of HgTe QWs are explained by graphene-like screening. We provide the comparison of the screening function for the Schrodinger fermions in the inverted bands HgTe QW with the appropriate screening function for graphene monolayer with the Dirac fermions. In addition, the dependencies of HgTe-specific screening function on temperature, scattering wave-vector and frequency are studied with the purpose to study the transport properties under high-frequency radiation the QWs structures to be used as THz detectors. Plasmon frequencies of 2DEG in HgTe quantum well under study were calculated in the long-wavelength limit for T=77K.

Vorticity-induced negative nonlocal resistance in a viscous two-dimensional electron system

We report non-local electrical measurements in a mesoscopic size two-dimensional (2D) electron gas in a GaAs quantum well in a hydrodynamic regime. Viscous electric flow is expected to be dominant when electron-electron collisions occur more often than the impurity or phonon scattering events. We observe a negative nonlocal resistance and attribute it to the formation of whirlpools in the electron flow. We use the different nonlocal transport geometries and compare the results with a theory demonstrating the significance of hydrodynamics in mesoscopic samples.

Viscous electron flow in mesoscopic two-dimensional electron gas

We report electrical and magneto transport measurements in mesoscopic size, two-dimensional (2D) electron gas in a GaAs quantum well. Remarkably, we find that the probe configuration and sample geometry strongly affects the temperature evolution of local resistance. We attribute all transport properties to the presence of hydrodynamic effects. Experimental results confirm the theoretically predicted significance of viscous flow in mesoscopic devices.

Optical conductivity of a quantum electron gas in a Sierpinski carpet

Recent advances in nanofabrication methods have made it possible to create complex two-dimensional artificial structures, such as fractals, where electrons can be confined. The optoelectronic and plasmonic properties of these exotic quantum electron systems are largely unexplored. In this article, we calculate the optical conductivity of a two-dimensional electron gas in a Sierpinski carpet (SC). The SC is a paradigmatic fractal that can be fabricated in a planar solid-state matrix by means of an iterative procedure. We show that the optical conductivity as a function of frequency (i.e. the optical spectrum) converges, at finite temperature, as a function of the fractal iteration. The calculated optical spectrum features sharp peaks at frequencies determined by the smallest geometric details at a given fractal iteration. Each peak is due to excitations within sets of electronic state-pairs, whose wave functions are characterized by quantum confinement in the SC at specific length scales, related to the frequency of the peak.

Optical characteristics of finite temperature quantum electron gas

In this paper we study the propagation of elliptically polarized transverse electromagnetic waves in a quasineutral plasma with arbitrary degenerate electron fluid ranging from classical dilute to fully degenerate density regimes by using the appropriate collisional magnetohydrodynamics model, which incorporates the adiabatic quantum equation of states for high-frequency electron fluid compression and the Bohm quantum potential responsible for the collective quantum diffraction effect. Three distinct propagation modes are categorized corresponding to electron density regimes of dilute, intermediate, and fully degenerate plasmas. One of these modes is found to be purely of quantum mechanical origin and disappears in the absence of the quantum diffraction effect. The present generalized magnetohydrodynamics theory qualitatively describes key features of optical parameters and experimental data of dilute classical, semiconducting, and in fully degenerate plasmas. Different optical parameters, such as the refractive and absorption index of the new mode are investigated. It is shown that the optical response of the magnetized plasma with arbitrary degeneracy is essentially governed by three characteristic frequencies, namely, collision, plasmon, and cyclotron frequencies. The profound experimental minimum in the refractive index of arbitrary degenerate quantum plasmas and its dependence on the characteristic frequencies is studied in detail. Current investigation is of fundamental importance in high energy density and fusion plasma diagnostics and may provide key knowledge on the characteristics of astrophysical dense matter.

Spin precession and spin waves in a chiral electron gas: Beyond Larmor's theorem

Larmor's theorem holds for magnetic systems that are invariant under spin rotation. In the presence of spin-orbit coupling this invariance is lost and Larmor's theorem is broken: for systems of interacting electrons, this gives rise to a subtle interplay between the spin-orbit coupling acting on individual single-particle states and Coulomb many-body effects. We consider a quasi-two-dimensional, partially spin-polarized electron gas in a semiconductor quantum well in the presence of Rashba and Dresselhaus spin-orbit coupling. Using a linear-response approach based on time-dependent density-functional theory, we calculate the dispersions of spin-flip waves. We obtain analytic results for small wave vectors and up to second order in the Rashba and Dresselhaus coupling strengths $\alpha$ and $\beta$. Comparison with experimental data from inelastic light scattering allows us to extract $\alpha$ and $\beta$ as well as the spin-wave stiffness very accurately. We find significant deviations from the local density approximation for spin-dependent electron systems.

Coupling between graphene and intersubband collective excitations in quantum wells

Recently, strong light-matter coupling between the electromagnetic modes in plasmonic metasurfaces with quantum-engineering electronic intersubband transitions in quantum wells has been demonstrated experimentally (Benz et al., [14], Lee et al., [15]). These novel materials combining different two-dimensional electronic systems offer new opportunities for tunable optical devices and fundamental studies of collective excitations driven by interlayer Coulomb interactions. In this work, our aim is to study the plasmon spectra of a hybrid structure consisting of conventional two-dimensional electron gas (2DEG) in a semiconductor quantum well and a graphene sheet with an interlayer separation of a. This electronic bilayer structure is immersed in a nonhomgeneous dielectric background of the system. We use a simple model in which the graphene surface plasmons and both; the intrasubband and intersubband collective electron excitations in the quantum well are coupled via screened Coulomb interaction. Here we calculate the dispersion of these relativistic/nonrelativistic new plasmon modes taking into account the thickness of the quantum well providing analytical expressions in the long-wavelength limit.

Spin dephasing of a two-dimensional electron gas in a GaAs quantum well near odd filling factors

The coherent spin dynamics of a two-dimensional electron gas in a GaAs/AlGaAs quantum well is experimentally studied near the filling factors ν = 3 and 1. The nonmonotonic character of the dependence of the spin dephasing time of a Goldstone spin exciton on the filling factor is found experimentally. The observed effect can be due to the formation of a new spin relaxation channel, when the main state of the two-dimensional electron system is a spin-textured liquid.

Linear Magnetoresistance in a Quasifree Two-Dimensional Electron Gas in an Ultrahigh Mobility GaAs Quantum Well.

We report a high-field magnetotransport study of an ultrahigh mobility (μ[over ¯]≈25×10^{6} cm^{2} V^{-1} s^{-1}) n-type GaAs quantum well. We observe a strikingly large linear magnetoresistance (LMR) up to 33T with a magnitude of order 10^{5}% onto which quantum oscillations become superimposed in the quantum Hall regime at low temperature. LMR is very often invoked as evidence for exotic quasiparticles in new materials such as the topological semimetals, though its origin remains controversial. The observation of such a LMR in the "simplest system"-with a free electronlike band structure and a nearly defect-free environment-excludes most of the possible exotic explanations for the appearance of a LMR and rather points to density fluctuations as the primary origin of the phenomenon. Both, the featureless LMR at high T and the quantum oscillations at low T follow the empirical resistance rule which states that the longitudinal conductance is directly related to the derivative of the transversal (Hall) conductance multiplied by the magnetic field and a constant factor α that remains unchanged over the entire temperature range. Only at low temperatures, small deviations from this resistance rule are observed beyond ν=1 that likely originate from a different transport mechanism for the composite fermions.

Study of spin-polarized plasma driven by spin force in a two-dimensional quantum electron gas

We examine the collective spin-polarized density motion in an unmagnetized plasma under a high frequency electromagnetic (EM) wave modulation. Spin effect in a quantum plasma is considered for the first time at a finite temperature near the Fermi temperature with considering collisional damping. A nonlinear two-fluid spin quantum magnetohydrodynamic model is used and solved self-consistently. The nonlinear effect and the reducing g-factor enhance the spin-polarization, while the collisional damping decreases the spin polarization. Strong spin-polarization is derived and the contribution of the spin-polarized current to the EM wave is much larger than that of the classical current.

High-harmonic generation in a quantum electron gas trapped in a nonparabolic and anisotropic well

An effective self-consistent model is derived and used to study the dynamics of an electron gas confined in a nonparabolic and anisotropic quantum well. This approach is based on the equations of quantum hydrodynamics, which incorporate quantum and nonlinear effects in an approximate fashion. The effective model consists of a set of six coupled differential equations (dynamical system) for the electric dipole and the size of the electron gas. Using this model we show that: (i) High harmonic generation is related to the appearance of chaos in the phase space, as attested by related Poincar\'e sections; (ii) Higher order harmonics can be excited efficiently and with relatively weak driving fields by making use of chirped electromagnetic waves.

The Instability of Terahertz Plasma Waves in Two Dimensional Gated and Ungated Quantum Electron Gas**supported by National Natural Science Foundation of China (No. 10975114)

The instability of terahertz (THz) plasma waves in two-dimensional (2D) quantum electron gas in a nanometer field effect transistor (FET) with asymmetrical boundary conditions has been investigated. We analyze THz plasma waves of two parts of the 2D quantum electron gas: gated and ungated regions. The results show that the radiation frequency and the increment (radiation power) in 2D ungated quantum electron gas are much higher than that in 2D gated quantum electron gas. The quantum effects always enhance the radiation power and enlarge the region of instability in both cases. This allows us to conclude that 2D quantum electron gas in the transistor channel is important for the emission and detection process and both gated and ungated parts take part in that process.

Negative differential conductivity in quantum well with complex potential profile for electron–phonon scattering

The effect of phonon scattering on electrical conductivity (EC) of 2D electron gas in quantum well (QW) systems with a complicated potential profile is described. Dependence of QW electrical conductivity on QW parameters (such as QW width, Fermi level positions etc.) when phonon scattering is employed has been calculated. NDC in EC when it varies with width of the QW has been found.

Terahertz Plasma Waves in Two Dimensional Quantum Electron Gas with Electron Scattering**supported by National Natural Science Foundation of China (No. 10975114)

We investigate the Terahertz (THz) plasma waves in a two-dimensional (2D) electron gas in a nanometer field effect transistor (FET) with quantum effects, the electron scattering, the thermal motion of electrons and electron exchange-correlation. We find that, while the electron scattering, the wave number along y direction and the electron exchange-correlation suppress the radiation power, but the thermal motion of electrons and the quantum effects can amplify the radiation power. The radiation frequency decreases with electron exchange-correlation contributions, but increases with quantum effects, the wave number along y direction and thermal motion of electrons. It is worth mentioning that the electron scattering has scarce influence on the radiation frequency. These properties could be of great help to the realization of practical THz plasma oscillations in nanometer FET.