Interaction Of Conduction Electrons Research Articles

Nature of electrically detected magnetic resonance in highly nitrogen-doped 6H -SiC single crystals

This work focuses on unraveling electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) properties of n-type 6H silicon carbide (SiC) single crystals with high concentrations of uncompensated nitrogen (N) donors, which is essential for fundamental understanding of spin-related phenomena, developing spin-based devices, optimizing materials and devices, and advancing research in quantum information and spintronics. Utilizing low-temperature multifrequency EPR spectroscopy (9.4–395.12 GHz), we identified two intense signals labeled as S line and S1 line in the 6H-SiC crystals with ND–NA≈8×1018 and 4×1019cm−3. In addition, in 6H-SiC crystals with ND–NA≈8×1018cm−3, a low-intensity triplet from N donors substituting the quasicubic “k2” nonequivalent position (Nk2) was observed. The S line [g⊥=2.0029(2),g∥=2.0038(2)] was assigned to the exchange interaction of conduction electrons and Nk2, while the S1 line [g⊥=2.0030(2),g∥=2.0040(2)] is caused by the exchange spin coupling of localized N donors at the “k1” and “k2” positions. The S1 line was observed in high-frequency EDMR spectra of 6H-SiC with ND–NA≈8×1018cm−3, and its emergence was explained by an enhancement of the hopping conductivity due to the EPR-induced temperature increase mechanism. No EDMR spectra were found to occur in the 6H-SiC crystals with ND–NA≈4×1019cm−3, which is close to the critical donor concentration value for a semiconductor-metal transition. Thus it can be concluded that this N donor concentration is too high for the appearance of spin-dependent scattering and too low for the emergence of EPR-induced hopping mechanisms in 6H-SiC. Published by the American Physical Society 2024

Disorder induced cluster spin glass like state in MnFeSb

Hexagonal MnSb is a ferromagnet with Curie temperature and saturation magnetization values of 587 K and 110 emu/g, respectively. In this paper, the origin of the complex magnetic behavior of a single phase MnFe0.20Sb prepared using solid-state reaction method is examined. A thorough investigation of temperature dependent magnetization and magnetic relaxation measurements reveals the presence of a glassy like phase below 15 K. AC susceptibility measurements revealed the existence of a cluster glass-like state with a freezing temperature of 18 K. The presence of competing magnetic interactions and random occupation of Fe atoms at 2d site leads the system to exhibit a cluster glass state. Furthermore, resistivity measurements indicate that the material exhibits a Kondo-like behavior below 30 K and can be attributed to the interaction of conduction electrons with localized Mn moments.

The features of the magnetoresistance of carbon nanotubes modified with Fe

Two specimens of modified multi-wall carbon nanotubes (MWCNT) with a mass fraction of iron of 0.20 and 0.29 have been obtained by the method of metal reduction from aqueous salt solution. According to structural and phase investigations, modified MWCNT contain Fe3C, α-Fe (ferromagnetic phase), and iron oxides FeO and Fe2O3 (antiferromagnetic phases with a Néel temperature of 188 K and 260 K, respectively) particles up to 8 nm in size. It is experimentally found that for MWCNT modified simultaneously by several ferromagnetic phases with different coercive forces, a giant magnetoresistive effect is observed at room temperature. For MWCNT modified with only one ferromagnetic phase, the giant magnetoresistance has not been experimentally detected. With temperature decrease, the magnetoresistance dependence on magnetic field for such modified nanotubes acquires a specific butterfly-like form, which is characteristic of the magnetic ordering of ferromagnetic and antiferromagnetic phases due to exchange anisotropy. For MWCNT modified with only one ferromagnetic phase there has been an effect of asymmetric magnetoresistance, which is related to the presence in the specimen of inhomogeneous transverse Hall voltages due to the pronounced spin-orbit interaction of conduction electrons and magnetic moments of the magnetic phase, and an anisotropic magnetoresistive effect.

Effect of high‐density current electropulsing on corrosion cracking of titanium aluminide intermetallic

AbstractThe effect of electropulsing on the corrosion cracking of titanium aluminide produced by self‐propagating high‐temperature synthesis has been investigated. The electropulsing treatment led to improved corrosion resistance in sodium fluoride solution and also eliminated corrosion cracking at the α2/γ interface during corrosion in a solution of nitric and hydrofluoric acids. This behavior was attributed to thermal and athermal effects resulting from electropulsing and leading to the interaction of conduction electrons with the defect structure. The effect of magnetic field accompanying electropusling on depinning of dislocations also has been discussed. Support for this is provided on the basis of X‐ray diffraction analysis and microhardness testing.

Plasmon enhanced second harmonic generation by periodic arrays of triangular nanoholes coupled to quantum emitters

Optical properties of periodic arrays of nanoholes of a triangular shape with experimentally realizable parameters are examined in both linear and nonlinear regimes. By utilizing a fully vectorial three-dimensional approach based on the nonlinear hydrodynamic Drude model describing metal coupled to Maxwell's equations and Bloch equations for molecular emitters, we analyze linear transmission, reflection, and nonlinear power spectra. Rigorous numerical calculations demonstrating second and third harmonic generation by the triangular hole arrays are performed. It is shown that both the Coulomb interaction of conduction electrons and the convective term contribute on equal footing to the nonlinear response of metal. It is demonstrated that the energy conversion efficiency in the second harmonic process is the highest when the system is pumped at the localized surface plasmon resonance. When molecular emitters are placed on a surface of the hole array line shapes, the second harmonic signal exhibits three peaks corresponding to second harmonics of the localized surface plasmon mode and upper and lower polaritonic states.

Electron Spin Current and Spin-Dependent Galvanomagnetic Phenomena in Metals

A system of coupled kinetic equations for the electron density and spin density distribution functions has been obtained based on the quantum kinetic equation. The collision integrals in the kinetic equations are written for an arbitrary scattering potential, taking into account the spin-orbit interaction of conduction electrons with scattering defects. As applied to the spin system of conduction electrons, the idea of a “reduced” description of transport phenomena is developed. The description of the system in terms of distribution functions depending on the quasi-momentum of electrons reduces to a description in terms of macroscopic mean quantities: electron density, spin density, electron flux, and spin current.

Anomalous Hall effect driven by dipolar spin waves in uniform ferromagnets

A new type of anomalous Hall effect is shown to arise from the interaction of conduction electrons with dipolar spin waves in ferromagnets. This effect exists even in homogeneous ferromagnets without relativistic spin-orbit coupling. The leading contribution to the Hall conductivity is proportional to the chiral spin correlation of dynamical spin textures and is physically understood in terms of the skew scattering by dipolar magnons.

Nanostructured TTT(TCNQ)2 Organic Crystals as Promising Thermoelectric n-Type Materials: 3D Modeling

Thermoelectric properties of quasi-one-dimensional TTT(TCNQ)2 organic crystals are investigated in order to appreciate the prospect of using this compound as n–type thermoelectric material. A more complete three-dimensional (3D) physical model is elaborated. It takes into account two the most important interactions of conduction electrons with longitudinal acoustic phonons, the electrons’ scattering on neighbor molecular chains, as well as the scattering by impurities and defects. The electrical conductivity, thermopower, the power factor, electronic thermal conductivity and the thermoelectric figure of merit in the direction along conductive molecular chains are calculated numerically for different degrees of crystal purity. It is shown that in stoichiometric compounds the thermoelectric figure of merit ZT remains small even after the increase of crystal perfection degree. The thermoelectric properties may be significantly enhanced by simultaneous increase of crystal perfection and of electron concentration. The latter can be achieved by additional doping with donors. For less pure crystals, the interaction with impurities predominates over the weak interchain interaction and the simpler one-dimensional (1D) physical model is applicable. When the impurity scattering is reduced, the interchain interaction begins to limit the carrier mobility and the application of the 3D physical model is required. The optimal parameters permitting to predict ZT~ 1 are determined.

Inhomogeneous Charge Distribution in Semiconductor Nanoparticles

The inhomogeneous spatial distribution of charge carriers within semiconductor oxide nanoparticles is investigated by taking into account processes involving the interaction of conduction electrons with oxygen donor vacancies in the bulk and with oxygen adsorbates at the surface. The main characteristics of the semiconductor nanoparticles, such as the surface charge, the distributions of positive and negative charges in the bulk, and the temperature dependence of the concentration of conduction electrons, are determined self-consistently by taking into account the interaction of all charges in the system under conditions of complete thermodynamic equilibrium. The developed statistical mechanics model allows us to determine the net surface negative charge on oxygen atoms, the spatial distributions of the conduction electrons, the positively charged ionized donors, and the electrical potential inside the nanoparticle as a function of nanoparticle radius and temperature.

Variation in electromagnetic radiation during plastic deformation under tension and compression of metals

This paper presents some significant variations in the intermittent electromagnetic radiation (EMR) during plastic deformation under tension and compression of some metals with selected crystal structure, viz. zinc, hexagonal closed packed (hcp), copper, face-centred cubic (fcc: stacking fault energy 0.08 J/m2), aluminium (fcc: stacking fault energy 0.2 J/m2) and 0.18 % carbon steel, body-centred cubic (bcc). The intermittent EMR signals starting near yielding are either oscillatory or exponential under both modes of deformation except a very few intermediate signals, random in nature, in zinc under compression. The number and amplitude of EMR signals exhibit marked variations under tension and compression. The smooth correlation between elastic strain energy release rate and average EMR energy release rate suggests a novel technique to determine the fracture toughness of metals. The first EMR emission amplitude and EMR energy release rate occurring near the yield increase, but maximum EMR energy burst frequency decreases almost linearly with increase in Debye temperature of the metals under tension while all EMR parameters decrease nonlinearly under compression. These results can be developed into a new technique to evaluate dislocation velocity. The EMR amplitude and energy release rate of the first EMR emission vary parabolically showing a maxima with increase in electronic heat constant of the metals under tension while they first sharply decrease and then become asymptotic during compression. However, the variation in EMR maximum energy burst frequency is apparently similar under both modes of deformation. These results strongly suggest that the mechanism of EMR emission during plastic deformation of metals involves not only the interaction of conduction electrons with the lattice periodic potential as presented in the previous theoretical models but also the interaction of conduction electrons with phonons. However, during crack propagation and fracture, charge oscillations at fractured surfaces due to breaking of atomic bonds constitute an additional factor.

Focusing of electrons by a transverse magnetic field

The foundations of the focusing of electrons by a transverse magnetic field proposed by V.S. Tsoi in 1974 have been reviewed. The kinetics of electrons in condensed media and interactions of conduction electrons with interfaces has been studied by means of the focusing of electrons. Various applications of the focusing of charge carriers in low-dimensional, including two-dimensional, electron systems have been demonstrated.

Operando Spectromicroscopy Observation of Many-Body Effects in Graphene Device

Linear band dispersion causes peculiar behaviour of device interfaces in graphene transistors. The vanishment of density of states (DOS) near the Dirac point due to the linear band dispresion renormalizes quasiparticles behaviours of electrons, i.e. many-body effects, such as excitonic effects and the Anderson orthogonality catastrophe (AOC) which occur through the interactions of conduction electrons with holes. For this reason, we have studied the impact of the excitonic effects and the AOC on graphene device performance by using x-ray absorption spectromicroscopy on an actual graphene transistor in operation. Our work shows that the excitonic effect and the AOC are tunable by gate bias or metal contacts, both of which alter the Fermi energy. In addition, it is found that these many-body effects are orbital-specifi c, appreciable many-body effects on π * orbital, while negligible on σ * orbital.

Cubic Topological Kondo Insulators

Current theories of Kondo insulators employ the interaction of conduction electrons with localized Kramers doublets originating from a tetragonal crystalline environment, yet all Kondo insulators are cubic. Here we develop a theory of cubic topological Kondo insulators involving the interaction of Γ(8) spin quartets with a conduction sea. The spin quartets greatly increase the potential for strong topological insulators, entirely eliminating the weak topological phases from the diagram. We show that the relevant topological behavior in cubic Kondo insulators can only reside at the lower symmetry X or M points in the Brillouin zone, leading to three Dirac cones with heavy quasiparticles.

Majorana-Klein Hybridization in Topological Superconductor Junctions

We present a powerful and general approach to describe the coupling of Majorana fermions to external leads, of interacting or noninteracting electrons. Our picture has the Klein factors of bosonization appearing as extra Majorana fermions hybridizing with the physical ones. We demonstrate the power of this approach, analyzing a highly nontrivial SO(M) Kondo problem arising in topological superconductors with M Majorana-lead couplings, allowing for arbitrary M and for conduction electron interactions. Mapping the problem on a quantum Brownian motion model we find robust non-Fermi liquid behavior, even for Fermi liquid leads, and a quantum phase transition between insulating and Kondo regimes when the leads form Luttinger liquids. In particular, for M=4 we find a stable realization of the two-channel Kondo fixed point. Obtaining the linear conductance at low temperatures, we predict transport signatures of this Majorana-Kondo-Luttinger physics.

Spin current-induced by a sound wave

The interaction of conduction electrons with a longitudinal sound wave propagating in a crystal in a constant magnetic field is investigated. It is shown that the transverse spin current arises when the longitudinal sound wave propagation through the system. The average power absorbed by the spin subsystem of the conduction electrons and the spin-Hall conductivity have a resonant character.

Microwave-induced spin-flip scattering of electrons in point contacts

We investigate resonant interaction of conduction electrons with an electromagnetic field that irradiates a point contact between a ferromagnetic and a normal metal in the presence of a strong magnetic field of order 1 T. We show that electron spin-flips caused by resonant absorption and stimulated emission of photons result in a sharp peak in the magnetic-field dependence of the point-contact resistance. The height of the peak is shown to be directly proportional to the net rate of energy transfer to the electromagnetic field in the point contact due to absorption and stimulated emission of photons. Estimations indicate that our theory can serve as a basis for the explanation of recent experiments [A.M. Kadigrobov et al., New J. Phys. 13, 023007 (2011)].

Oscillations of kinks on dislocation lines in crystals and low-temperature transport anomalies as a “passport” of newly-induced defects

The possible interpretation of experimental data on low-temperature anomalies in weakly deformed metallic crystals prepared form ultra-pure lead, copper, and silver, as well as in crystals of 4He is discussed within the previously proposed theoretical picture of dislocations with dynamical kinks. In the case of pure metals the theoretical predictions give a general picture of interaction of conduction electrons in a sample with newly-introduced dislocations, containing dynamic kinks in the Peierls potential relief. In the field of random stresses appearing due to plastic deformation of a sample, kinks on the dislocation line form a set of one-dimensional oscillators in potential wells of different shapes. In the low temperature region at low enough density of defects pinning kinks the inelastic scattering of electrons on kinks should lead to deviations from the Wiedemann-Franz law. In particular, the inelastic scattering on kinks should result in a quadratic temperature dependence of the thermal conductivity in a metallic sample along preferential directions of dislocation axes. In the plane normal to the dislocation axis the elastic large-angle scattering of electrons is prevalent. The kink pinning by a point defect or by additional dislocations as well as the sample annealing leading to the disappearance of kinks should induce suppression of transport anomalies. Thus, the energy interval for the spectrum of kink oscillations restricted by characteristic amplitude of the Peierls relief is a “passport of deformation history” for each specific sample. For instance, in copper the temperature/energy region of the order of 1 K corresponds to it. It is also planned to discuss in the other publication applicability of mechanism of phonon scattering on mobile dislocation kinks and pinning of kinks by impurities in order to explain anomalies of phonon thermal conductivity of 4He crystals and deformed crystals of pure lead in a superconducting state.

EPR study of conduction electrons in heavily doped n-type 4H SiC

The magnetic properties of conduction electrons (CE) in heavily doped n-type 4H SiC have been studied with electron paramagnetic resonance (EPR) in the temperature interval from 7 to 140 K. An EPR line with “Dyson lineshape” was observed in 4H SiC wafers with (ND–NA) ≈ 1019 cm−3. The EPR line is composed of two overlapping lines with Lorentzian and Dysonian lineshape, which are responsible for the localized and delocalized spin systems attributed to electrons localized on the nitrogen donors (LE) and CE, respectively. The Dysonian line is characterized by an asymmetry parameter R. The coupling between the two spin systems, which are characterized by S = 1/2 is realized via an exchange interaction of CE with the LE. As a result the g-factor of the Dysonian spectral line is governed by an exchange interaction between LE and CE and was evaluated as g|| = 2.0045, g⟂ = 2.0003. The temperature dependence of the integral intensity of the CE EPR signal is described by the sum of Curie–Weiss and Pauli paramagnetism. The Curie-like contribution arises from unpaired spins in the impurity band of heavily doped 4H SiC, while a Pauli-like contribution that becomes noticeable at T > 80 K indicates the presence of the CE in the conduction band. From the analysis of the temperature dependence of R(T) and the linewidth ΔH(T) of the CE EPR signal the activation energy of the CE into the conduction band was estimated to be 39.4 meV. The obtained value of the activation energy coincides with that for nitrogen donors forming an impurity band in heavily doped n-type 4H SiC. Thus, the temperature behavior of the CE spin system in highly doped 4H SiC can be interpreted in terms of electrons that are freely moving over the impurity and conduction band. The CE present in the impurity band are strongly coupled with LE by cross-relaxation processes.

Superconductivity in the Kondo lattice model

We study the Kondo lattice model with additional attractive interaction between the conduction electrons within the dynamical mean-field theory using the numerical renormalization group to solve the effective quantum impurity problem. In addition to normal-state and magnetic phases we also allow for the occurrence of a superconducting phase. In the normal phase we observe a very sensitive dependence of the low-energy scale on the conduction-electron interaction. We discuss the dependence of the superconducting transition on the interplay between attractive interaction and Kondo exchange.

Mechanisms of electron scattering in (3HgSe)1–x (Al2Se3) x crystals doped with manganese

Investigation of electron scattering in (3HgSe)1–x(Al2Se3)x: crystals (NMn ~ 10 cm) at the temperatures Т = 77–300 K, i.e., in a temperature range where the effect of the exchange interaction of conduction electrons with d-electrons of Mn on the kinetic phenomena is weak [1, 2], could be performed using the relations obtained for undoped semiconductors. In the relations reported in [3] for the main kinetic coefficients of a degenerate semiconductor in any magnetic field it is assumed that electron energy E depends on the value of wave vector k only, which covers all the cases of the spherically-symmetric nonparabolic bands. The calculations in [3] are performed within an approximation of relaxation timeτ. The specific dependence of τ on energy Е was not however included into consideration (it is assumed that τ is an arbitrary function of E), so the formulas obtained in [3] are also valid for the case of a mixed scattering mechanism.