Magnetized Electron Gas Research Articles

Thermodynamic limit for the magnetic uniform electron gas and representability of density-current pairs

Although the concept of the uniform electron gas is essential to quantum physics, it has only been defined recently in a rigorous manner by Lewin, Lieb and Seiringer. We extend their approach to include the magnetic case, by which we mean that the vorticity of the gas is also held constant. Our definition involves the grand-canonical version of the universal functional introduced by Vignale and Rasolt in the context of current-density-functional theory. Besides establishing the existence of the thermodynamic limit, we derive an estimate on the kinetic energy functional that also gives a convenient answer to the (mixed) current-density representability problem.

High-Mobility Magnetic Two-Dimensional Electron Gas in Engineered Oxide Interfaces

The engineered interfaces of complex oxides have abundant physical properties and provide a powerful platform for the exploration of fundamental physics and emergent phenomena. In particular, research on the two-dimensional magnetic systems with high mobility remains a long-standing challenge for the discovery of quantum phase and spintronic applications. Here, we introduce a few atomic layers of the delta doping layer at LaAlO3/SrTiO3 interfaces through elaborately controllable epitaxial growth of SrRuO3. After inserting a SrRuO3 buffer layer, the interfaces exhibit a well-defined anomalous Hall effect up to 100 K and their mobility is enhanced by 3 orders of magnitude at low temperatures. More intriguingly, a large unsaturated positive magnetoresistance is created at interfaces. Combining with the density functional theory calculation, we attribute our findings to the electron transfer at interfaces and the magnetic moment of Ru4+ 4d bands. The results pave a way for further research of two-dimensional ferromagnetism and quantum transport in all-oxide systems.

Group velocity of bulk magnetoplasmons in electric-gyrotropic thin films: Faraday configuration

The behaviors of bulk magnetoplasmon waves in a magnetized electron gas thin film in the Faraday configuration, as an example of an electric-gyrotropic film, are investigated. General expression for dispersion relation of the waves is obtained by two different approaches. Also, energy distribution and power flow of bulk and surface magnetoplasmon waves are studied. Furthermore, the group velocity and associated group delay time of bulk magnetoplasmon modes are obtained exactly by several different theoretical methods, such as the well-known wave theory method, the zig-zag ray approach based on the stationary-phase method and also the zig-zag ray approach based on the energy concepts. It is shown that the results are in completely consistent with each other.

Strongly direction-dependent magnetoplasmons in mixed Faraday\u2013Voigt configurations

The electrostatic theory of surface magnetoplasmons on a semi-infinite magnetized electron gas is generalized to mixed Faraday–Voigt configurations. We analyze a mixed Faraday–Voigt type of electrostatic surface waves that is strongly direction-dependent, and may be realized on narrow-gap semiconductors in the THz regime. A general expression for the dispersion relation is presented, with its dependence on the magnitude and orientation of the applied magnetic field. Remarkably, the group velocity is always perpendicular to the phase velocity. Both velocity and energy relations of the found magnetoplasmons are discussed in detail. In the appropriate limits the known surface magnetoplasmons in the higher-symmetry Faraday and Voigt configurations are recovered.

Response tensor for a spin-dependent electron gas: Dependence on the choice of spin operator.

It is shown that the choice of spin operator affects the form of the response tensor describing a spin-dependent electron gas. The covariant, spin-dependent response tensor for a magnetic dipole moment-polarized electron gas (statistical distribution of electrons and positrons) is evaluated. A simultaneous eigenfunction of both the magnetic-moment spin operator and the Dirac Hamiltonian is constructed, from which explicit expressions for the magnetic-moment states and the corresponding vertex functions are derived. It is shown that a gas of electrons having a preferred magnetic-moment spin has a rotatory-type response that is gyrotropic. In contrast, when the helicity is chosen as the spin operator, the response of an electron gas with a preferred helicity spin has a rotatory response that is analogous to an optically active medium. The distinction between these spin operators does not appear in conventional treatments of spin dependence in quantum plasmas.

Dispersive electrostatic waves on a cold magnetized electron gas half-space

Dispersive electrostatic waves on the plane interface between a vacuum and a cold magnetized homogeneous electron gas are predicted for the case where an applied static magnetic field is parallel to the surface and the direction of propagation of the wave, known as Faraday configuration, and also static magnetic field is weakly non-uniform in a direction which is perpendicular to the surface. An expression for dispersion relation of these surface waves is presented based on the Wentzel–Kramers–Brillouin approximation. The dispersion relation shows the importance of the influence of the external static magnetic field gradient on the surface wave behavior.

Origin of the magnetic spin Hall effect: Spin current vorticity in the Fermi sea

The interplay of spin-orbit coupling (SOC) and magnetism gives rise to a plethora of charge-to-spin conversion phenomena that harbor great potential for spintronics applications. In addition to the spin Hall effect, magnets may exhibit a magnetic spin Hall effect (MSHE), as was recently discovered [Kimata \textit{et al.}, Nature \textbf{565}, 627-630 (2019)]. To date, the MSHE is still awaiting its intuitive explanation. Here we relate the MSHE to the vorticity of spin currents in the Fermi sea, which explains pictorially the origin of the MSHE. For all magnetic Laue groups that allow for nonzero spin current vorticities the related tensor elements of the MSH conductivity are given. Minimal requirements for the occurrence of a MSHE are compatibility with either a magnetization or a magnetic toroidal quadrupole. This finding implies in particular that the MSHE is expected in all ferromagnets with sufficiently large SOC. To substantiate our symmetry analysis, we present various models, in particular a two-dimensional magnetized Rashba electron gas, that corroborate an interpretation by means of spin current vortices. Considering thermally induced spin transport and the magnetic spin Nernst effect in magnetic insulators, which are brought about by magnons, our findings for electron transport can be carried over to the realm of spincaloritronics, heat-to-spin conversion, and energy harvesting.

Density functional theory of magnetic dipolar interactions

We propose a way to include magnetic dipole-dipole interactions in density functional theory calculations. To this end, we derive an approximation to the exchange-correlation energy functional associated with the spin-spin correction to the Coulomb force in the Breit-Pauli Hamiltonian. The local spin-density approximation is shown to be identically zero. First order nonlocal corrections are evaluated analytically within linear response to a noncollinear external magnetic field. The functional obtained is based on the exact-exchange energy of the magnetic electron gas with dipolar interactions and is estimated to be relevant at interatomic distances, or in the low electron density limit, where it amounts to one quarter of the magnetostatic energy. We expect our functional to improve over the current description of ground-state properties of inhomogeneous magnetic structures at the nanoscale and dipolar spin systems.

Magnetic two-dimensional field effect transistor

We study experimentally low-temperature current-voltage characteristics of n-type GaAs/GaAlAs modulation doped quantum wells under the influence of an external magnetic field. In particular, we use samples additionally doped in the well with Be acceptors. As showed previously, negatively charged acceptor ions can localize conduction electrons by a joint effect of a quantum well and an external magnetic field. It is found that, in the acceptor-doped samples, the Hall electric field resulting from the presence of magnetic field plays the role of the gate voltage. At sufficiently high magnetic fields, the drain current has a constant value independent of the drain voltage. It is argued that the above phenomenon is due to the electron localization with the resulting decrease of conducting electron density in the crossed-field configuration. We propose to exploit the observed unusual behaviour as a device called “magnetic two-dimensional electron gas field effect transistor” operating at low temperatures.

The Diamagnetic Phase Transition of Dense Electron Gas: Astrophysical Applications

Neutron stars are ideal astrophysical laboratories for testing theories of the de Haas–van Alphen effect and diamagnetic phase transition which is associated with magnetic domain formation. The “magnetic interaction” between delocalized magnetic moments of electrons (the Shoenberg effect), can result in an effect of the diamagnetic phase transition into domains of alternating magnetization (Condon's domains). Associated with the domain formation are prominent magnetic field oscillation and anisotropic magnetic stress which may be large enough to fracture the crust of magnetar with a super-strong field. Even if the fracture is impossible as in “low-field” magnetar, the depinning phase transition of domain wall (DW) motion driven by low field rate (mainly due to the Hall effect) in the randomly perturbed crust can result in a catastrophically variation of magnetic field. This intermittent motion, similar to the avalanche process, makes the Hall effect be dissipative. These qualitative consequences about magnetized electron gas are consistent with observations of magnetar emission, and especially the threshold critical dynamics of driven DW can partially overcome the difficulties of “low-field” magnetar bursts and the heating mechanism of transient, or “outbursting” magnetar.

The Physics of Magnetars II - The Electron Fermi Energy of and the Origin of High X-ray Luminosity of Magnetars

In this paper we discuss in detail the quantization of Landau energy levels of a strongly magnetized and completely degenerate relativistic electron gas in neutron stars. In particular, we focus on the Fermi energy dependence of the magnetic field for a relativistic electron gas in the superstrong magnetic field of magnetars. We would like to point out that some of the results concerning the microscopic number density of states of a strongly magnetized electron gas given by well known statistical physics text books are incorrect. The repeated use of these results in the last five decades probably seriously affects the physics of neutron stars and magnetars. The quantization of Landau energy levels is accurately delineated in terms of the Dirac -δ function. Relatively simple calculation shows that the Fermi energy of a relativistic electron gas in magnetars with superstrong magnetic fields (B>B cr , here B cr is the Landau critical magnetic field, B cr = 4.414 × 10 13 gauss ) increases with magnetic field strength as B 1/4 . On the basis of this simple but important new result we are leading naturally to propose a new mechanism for the production of high X-ray luminosity from magnetars.

Рух іона в замагніченому електронному газі як розсіяння в деформованому кулонівському потенціалі

Рух іона в замагніченому електронному газі як розсіяння в деформованому кулонівському потенціалі

Strongly self‐magnetized quantum relativistic electron gas expanding as a jet

AbstractWe discuss the behavior of a strongly magnetized electron gas whose dominant pressure is exerted along the applied field, and extends along it as a one dimensional system. We suggest a model for maintaining the magnetic field selfconsistently, and for it we conjecture a partial bosonization of the electron gas, described by a charged vector boson field which experiences condensation, leading to a ferromagnetic behavior. Our aim is to suggest a possible quantum relativistic self‐magnetized jet model. High frequency photons will be deviated also along paths parallel to the external field. Any addition of energy to the electron system, would contribute mainly to increase the kinetic energy along the magnetic field axis, an the jet may grow in this way for long times. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetoresistance quantum oscillations in a magnetic two-dimensional electron gas

Magneto-transport measurements of Shubnikov-de Haas (SdH) oscillations have been performed on two-dimensional electron gases (2DEGs) confined in CdTe and CdMnTe quantum wells. The quantum oscillations in CdMnTe, where the 2DEG interacts with magnetic Mn ions, can be described by incorporating the electron-Mn exchange interaction into the traditional Lifshitz-Kosevich formalism. The modified spin splitting leads to characteristic beating pattern in the SdH oscillations, the study of which indicates the formation of Mn clusters resulting in direct anti-ferromagnetic Mn-Mn interaction. The Landau level broadening in this system shows a peculiar decrease with increasing temperature, which could be related to statistical fluctuations of the Mn concentration.

Spin current swapping and Hanle spin Hall effect in a two-dimensional electron gas

We analyze the effect known as ``spin current swapping'' (SCS) due to electron-impurity scattering in a uniform spin-polarized two-dimensional electron gas. In this effect a primary spin current ${J}_{i}^{a}$ (lower index for spatial direction, upper index for spin direction) generates a secondary spin current ${J}_{a}^{i}$ if $i\ensuremath{\ne}a$, or ${J}_{j}^{j}$, with $j\ensuremath{\ne}i$, if $i=a$. Contrary to naive expectation, the homogeneous spin current associated with the uniform drift of the spin polarization in the electron gas does not generate a swapped spin current by the SCS mechanism. Nevertheless, a swapped spin current will be generated, if a magnetic field is present, by a completely different mechanism, namely, the precession of the spin Hall spin current in the magnetic field. We refer to this second mechanism as Hanle spin Hall effect, and we notice that it can be observed in an experiment in which a homogeneous drift current is passed through a uniformly magnetized electron gas. In contrast to this, we show that an unambiguous observation of SCS requires inhomogeneous spin currents, such as those that are associated with spin diffusion in a metal, and no magnetic field. An experimental setup for the observation of the SCS is therefore proposed.

Intraband and interband spin-orbit torques in noncentrosymmetric ferromagnets

Intraband and interband contributions to the current-driven spin-orbit torque in magnetic materials lacking inversion symmetry are theoretically studied using Kubo formula. In addition to the current-driven field-like torque ${\bf T}_{\rm FL}= \tau_{\rm FL}{\bf m}\times{\bf u}_{\rm so}$ (${\bf u}_{\rm so}$ being a unit vector determined by the symmetry of the spin-orbit coupling), we explore the intrinsic contribution arising from impurity-independent interband transitions and producing an anti-damping-like torque of the form ${\bf T}_{\rm DL}= \tau_{\rm DL}{\bf m}\times({\bf u}_{\rm so}\times{\bf m})$. Analytical expressions are obtained in the model case of a magnetic Rashba two-dimensional electron gas, while numerical calculations have been performed on a dilute magnetic semiconductor (Ga,Mn)As modeled by the Kohn-Luttinger Hamiltonian exchanged coupled to the Mn moments. Parametric dependences of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described.

Semiconductor nanotube plasma

The theory of dispersion of surface plasma waves in semiconductor nanotubes is presented. The effect of screening the Coulomb field of a static point charge by a magnetized electron gas of a nanotube is investigated. The main properties of the semiconductor nanotube plasma, 3D plasma, and planar 2D plasma are compared. The dependences of the critical temperature and thermodynamic properties of a superconducting quantum cylinder on the characteristics of the system are studied.

Decay of a massive neutrino in magnetized electron gas

This paper contains a summarized calculation of the probability of massive Dirac neutrino radiative decay in an intense magnetic external field where $H\ensuremath{\gtrsim}{H}_{0}={m}_{e}^{2}{c}^{3}/e\ensuremath{\hbar}=4.41\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }\mathrm{G}$ with a degenerated electron gas present. It is demonstrated that the presence of the said medium significantly increases the probability of neutrino decay in the magnetic field, both in cases of relativistic and nonrelativistic neutrinos. The latter conclusion is of interest in connection with the currently developed dark matter theories, according to which dark matter may consist of nonrelativistic neutrinos with mass equal to several keV.

The electromagnetic mechanism of plasmon decay to a neutrino pair in a strongly magnetized electron gas

An expression for the neutrino luminosity of a degenerate electron gas in a strong magnetic field via plasmon decay to a neutrino pair due to electromagnetic neutrino moments is derived. The neutrino luminosity of the medium in an electromagnetic reaction channel is shown to be comparable with the luminosity in a weak channel. The relative upper bounds for the effective magnetic neutrino moment are obtained.

Weak and electromagnetic mechanisms of neutrino-pair photoproduction in a strongly magnetized electron gas

Expressions for the power of neutrino radiation from a degenerate electron gas in a strong magnetic field are derived for the case of neutrino-pair photoproduction via the weak and electromagnetic interaction mechanisms (it is assumed that the neutrino possesses electromagnetic form factors). It is shown that the neutrino luminosity of a medium in the electromagnetic reaction channel may exceed substantially the luminosity in the weak channel. Relative upper bounds on the effective neutrino magnetic moment are obtained.