Conduction Electron Wave Functions Research Articles

Electrophysical Properties of Onion-Like Carbon

The paper examines electrophysical properties of onion-like carbon (OLC) samples, where particles have the average size of 4–8 nm and are formed by 5–10 nested fullerene-like spheres connected by 1-3 common curved graphene shells into aggregates with a size of 50–300 nm. We measured the temperature dependence of electrical resistance from 4.2 to 300 K and dependence of magnetoresistance in magnetic fields up to 6 T at the temperature of 4.2 K. Temperature dependences of electrical resistance of samples can be described within the framework of the Mott law with variable hop length for the one-dimensional case or within the framework of the Efros–Shklovskii Coulomb gap. We observed the quadratically increasing positive magnetoresistance up to 6 T associated with compression of wave functions of conduction electrons. Negative magnetoresistance was observed in the range of magnetic fields up to 1–2 T in the case of some samples. This is due to the fact that magnetic field suppresses the contributions to magnetoresistance made by interference effects in the area of hopping conductivity. The measurements were used to estimate the localization radius that is comparable to the diameter of OLC particles (nano-onions).

Pseudorelativistic effects on solitons in quantum semiconductor plasma

A theory for nonlinear excitations in quantum plasmas is presented for narrow-gap semiconductors by considering the combined effects of quantum and pseudorelativity. The system is governed by a coupled Klein-Gordon equation for the collective wave functions of the conduction electrons and Poisson's equation for the electrostatic potential. This gives a closed system, including the effects of charge separation, quantum tunneling, and pseudorelativity. By choosing the typical parameters of semiconductor InSb, the quasistationary soliton solution, which is a multipeaked dark soliton, is obtained numerically and shows depleted electron densities correlated with a localized potential. The dynamical simulation result shows that the dark soliton is stable and has a multipeaked profile, which is consistent with the quasistationary solution. The present model and results may be useful in understanding the nonlinear properties of semiconductor plasma on an ultrafast time scale.

Persistent Current Generation by the Spin-Vortex Formation in the Cuprate with the Single-Valuedness Constraint on the Conduction Electron Wave Functions

The persistent current generation in the cuprate is theoretically investigated based on the spin-vortex superconductivity theory. We present a way to impose the single-valued condition on wave functions and clarify the appearance of a vector potential and the persistent current generation by it when the spin-vortices are created by the conduction electrons. We attribute the reason for the very high superconducting transition temperature in the cuprate to the enhanced stability of the spin-vortices by the strong hole–lattice interaction.

Interactions between conduction and magnetic electrons in europium chalcogenides

This paper is devoted to spin-orbit interactions between conduction and magnetic electrons. A model is proposed where the spin-orbit mechanism arises from intra-ionic spin-orbit coupling due to hybridization of conduction and magnetic electron wave functions. The physical consequences of spin-orbit interactions, e.g., the anomalous Hall effect, magnon amplification, and magnon drag, are discussed briefly.

B11NMR in the layered diboridesOsB2andRuB2

$^{11}\mathrm{B}$ nuclear magnetic resonance (NMR) measurements have been performed on $^{11}\mathrm{B}$ enriched $\mathrm{Os}{\mathrm{B}}_{2}$ and $\mathrm{Ru}{\mathrm{B}}_{2}$ polycrystalline powder samples in an external field of $4.7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ and in the temperature range, $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}lTl300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The spectra for both samples show similar quadrupole powder patterns that are typical for a nonaxial symmetry. The Knight shifts $K$ in both samples are very small and constant in temperature. The nuclear spin-lattice relaxation rate ${T}_{1}^{\ensuremath{-}1}$ follows a Korringa law in the whole temperature range investigated with ${T}_{1}T=600$ and $680\phantom{\rule{0.3em}{0ex}}\mathrm{sK}$ for $\mathrm{Os}{\mathrm{B}}_{2}$ and $\mathrm{Ru}{\mathrm{B}}_{2}$, respectively. The experimental results indicate that a $p$ character dominates the conduction electron wave function at the B site with a negligibly small $s$ character in both compounds.

Hot-phonon effect on power dissipation in a biasedAlxGa1−xN∕AlN∕GaNchannel

The Monte Carlo simulation of hot-electron energy dissipation is carried out for a biased $\mathrm{Al}\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ channel. The conduction band profile and electron wave functions are calculated through self-consistent solution of Poisson and Schr\"odinger equations. Nonelastic scattering of electrons on acoustic phonons and nonequilibrium longitudinal optical (LO) phonons is included. The nonequilibrium LO phonons are treated in terms of hot-phonon lifetime. The dependence of electron temperature and dissipated power on the applied electric field is obtained from the Monte Carlo simulation. The experimental results on noise temperature and current as functions of electric field strength applied along the channel are presented, and the dependence of the supplied electric power on the inverse electron temperature is evaluated. The best agreement between the Monte Carlo results and the experimental data is obtained for the hot-phonon lifetime ${\ensuremath{\tau}}_{\mathrm{ph}}=1\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$.

Low electron density of states at the boron site of TMB2 (TM = Ti, Zr, Hf, and Nb): a 11B NMR study

The local density of states at the boron site in TMB2 (TM=Ti, Zr, Hf, and Nb) has been examined using the solid-state 11B NMR technique. The magic angle spinning (MAS) NMR spectra at room temperature and the spin-lattice relaxation rates have been measured as functions of temperature (30–293K). The resonance line shifts are small and become more negative in the direction from 3d- to 5d-elements. The relaxation rates follow a linear law characteristic of hyperfine magnetic interaction with conduction electrons. With borides of IV group metals the data can be understood in terms of a very low s-electron density of states and absence of a p-character of the conduction electron wave function at the Fermi level while in the case of NbB2 a small partial p-electron density of states is assumed. Then, the results are in good agreement with the earlier theoretical prediction.

Room temperature Compton profiles of conduction electrons in α-Ga metal

Room temperature Compton profiles of momentum distribution of conduction electrons in α -Ga metal are calculated in band model. For this purpose, the conduction electron wave functions are determined in a temperature-dependent non-local model potential. The profiles calculated along the crystallographic directions, (100), (010), and (001) are found to be nearly isotropic. This conclusion is in reasonable agreement with experimental observations

Low temperature anomaly in mesoscopic kondo wires

We report the observation of an anomalous magnetoresistance in extremely dilute quasi-one-dimensional AuFe wires at low temperatures, along with a hysteretic background at low fields. The Kondo resistivity does not show the unitarity limit down to the lowest temperature, implying uncompensated spin states. We suggest that the anomalous magnetoresistance may be understood as the interference correction from the accumulation of geometric phase in the conduction electron wave function around the localized impurity spin.

Spatial and spectroscopic profiles of the Kondo resonance for magnetic atoms on metal surfaces

Manifestations of the Kondo effect on an atomic length scale on and around magnetic atoms adsorbed on a nonmagnetic metal surface differ depending on which spectroscopic mode the scanning tunneling microscope is operated. In a previous report [T. Kawasaka, H. Kasai, and A. Okiji, Phys. Lett. A 250, 403 (1998)], we suggested the possibility that the Kondo effect can be directly observed as protrusions (peaks) in the spatial distribution of the tunneling current. By comparing the spatial distributions of the conduction electron and localized electron wave function, we show that the protrusions (peaks) observed in the spatial distribution of the tunneling current correspond to the resonances observed in the differential conductance spectra. Furthermore, we investigate the temperature dependence of the spatial distribution of the tunneling current and of the differential conductance to study the electronic properties of various metal–adatom systems.

Solid-State NMR Structural Studies of the Ternary Molybdenum Cluster Chalcogenides CdxMo6Se8 (x = 1, 2)

The structures of the ternary Chevrel phases CdMo{sub 6}Se{sub 8} and Cd{sub 2}Mo{sub 6}Se{sub 8} have been studied by several complementary {sup 111}Cd NMR spectroscopic techniques. Specifically, cadmium mobility and bonding properties are probed by temperature and frequency dependent measurements of static line shapes, magic angle spinning (MAS) NMR spectra, and spin-lattice relaxation rates. Furthermore, models for the spatial cadmium distribution are tested on the basis of {sup 111}Cd-{sup 111}Cd dipole-dipole interactions, measured by spin-echo decay spectroscopy on isotopically labeled materials (97% {sup 111}Cd). CdMo{sub 6}Se{sub 8} undergoes a phase transition near 130 K; the cadmium ions are static on the NMR time scale over the whole temperature range in both phases. The spatial cation distribution is close to homogeneous, and it specifically excludes the presence of Cd-Cd dimers. For the high-temperature phase, the {sup 111}Cd spectra indicate a large degree of static disorder. In addition, the large {sup 111}Cd chemical shift temperature coefficient and fast spin-lattice relaxation reveal strong interactions between the intercalated cadmium atoms and the conduction band wave functions of the Mo{sub 6}Se{sub 8} matrix. This behavior is typical for charge-transfer intercalation compounds in which the conduction band is only partially filled. Cd{sub 2}Mo{sub 6}Se{sub 8}, whichmore » crystallizes in the rhombohedral R{bar 3} structure, shows the typical NMR signature of a rigid, semiconducting compound. The intercalated metal species show no apparent interaction with conduction electron wave functions. {sup 111}Cd MAS and spin-echo decay data suggest a disordered atomic distribution of Cd{sup 2+} ions with a minimum Cd-Cd internuclear distance of 258 pm.« less

Quantum size effect on optical second-harmonic generation in small metallic particles.

Second-order susceptibilities of small metallic particles are calculated by the quantum size effect, in which the wave functions of conduction electrons are constrained in a small sphere. The electric-quadrupole term, which plays an essential role in the second-harmonic generation in metals, varies inversely with different powers of the radius. The magnitude of the quadrupole susceptibility is enhanced by the quantum size effect as the particle size diminishes below 10 nm, and approaches the results evaluated from the free-electron-gas model as the particle radius goes to infinity. The enhancement of the second-harmonic reflectivity generated from small metallic particles, as calculated in this work, is in general agreement with experimental results.

Growth, Superconductivity and Anisotropy in the Electrical Resistivity of Pb2Sr2Ho0.5Ca0.5Cu3O8 Single Crystals: The Effect of Contamination from the Crucible on Tc

Single crystals of Pb2Sr2Ho0.5Ca0.5Cu3O8 have been grown in Pt, Al2O3 and Au crucibles by means of the flux method. The effect of contamination from the crucible on T c has been investigated by studing the effects of Cu-site substitution on T c and magnetic properties for sintered polycrystals of Pb2Sr2R0.5Ca0.5( Cu1-y My )3O8 with R= Ho or Y and M= Pt or Al. Consequently, it has been found that use of a Pt crucible leads to growth of single crystals of the best quality with high T c values and that Al2O3 and Au crucibles contaminate the single crystals to decrease T c. Anisotropy in the electrical resistivity of the single-crystal Pb2Sr2Ho0.5Ca0.5Cu3O8 has been found to be comparable to that of YBa2Cu3O7 in spite of its thick blocking layer, suggesting that the wave functions of conduction electrons moderately overlap along the c-axis in Pb2Sr2Ho0.5Ca0.5Cu3O8.

Electronic states in the presence of the inner-shell hole studied by the method of DV-Xα

The molecular orbital theory by the method of DV-Xα is applied to investigate electronic states of electrons in the presence of the inner-shell hole. The hole is assumed to be at the center of the cluster which is composed of nine ions in the bcc structure. Using the present model, the hole potential born by missing an outermost inner-shell hole is found not to be atomic but extended to the cluster size. The result is applied to investigate the anomalous edge of absorption spectra and the related problem of heavy alkali metals with the inner-shell hole in the final state. Phase shifts for l = 2 and l = 3 of wavefunctions of conduction electrons due to the presence of the inner-shell hole in the final state are found to be negative. For Cs, we could not obtain phase shifts that are consistent with both the results of experiments on X-ray absorption and XPS.

Electronic States and Superconductivity in Alkali-Intercalated Fullerides:13C-NMR Study in Na2RbC60, Na2CsC60, K3C60, K2RbC60, K2CsC60, KRbCsC60, Rb2CsC60and RbCs2C60

A systematic 13 C NMR experiment is reported in alkali-fullerides A 3 C 60 (where A 3 is alkali-metals) between superconducting transition temperature T c and ∼100 K. Careful 13 C NMR spin-lattice relaxation time study clarified the properties of the conduction electron wave functions at Fermi surface. An upper limit of Stoner exchange parameter was estimated to be ∼3 eV/(spin-carbon), which is far from spin-wave instability criterion. Based on these studies, a variation of the density of states at Fermi level, N ( E f ), with T c was deduced. The results were analyzed in terms of McMillan formula, leading to weak or medium electron-phonon coupling constants and relevant phonon energy larger than 600 K. It was strongly suggested that the A 3 C 60 superconductor is described within a framework of the conventional phonon-mediated BCS superconductivity.

Influence of the xenon induced work function change on the xenon binding energy in photoemission of adsorbed xenon

Photoemission of adsorbed xenon has been shown to probe the local atomic work function. The Xe binding energy has a constant value relative to the vacuum level causing the measured binding energy relative to the Fermi level to vary with the work function of the adsorption site. The alignment of the Xe core level to the vacuum level should result in peak shifts with the work function change caused by the adsorbed Xe since the substrate vacuum level shifts with this work function change. However, the Xe peak positions are invariant to the work function changes and remain aligned to the work function of the clean substrate. It is shown in this article how this invariance creates a paradox for the model of the Xe core levels aligned to the vacuum level. The paradox arises from the simultaneous invariance of the Xe and the substrate core level binding energies to the work function change along with the modified threshold for secondary electron emission. The work function change is typically described by a dipole field created by the adsorbed atom. However, this dipole field would alter the kinetic energy of the substrate photoelectrons as well as the secondary electron threshold. A compensating change in the contact potential difference could make the measured substrate levels constant but this would require the Xe level to shift which they do not. This is the basis of the paradox which cannot be resolved by ascribing the work function change to an electrostatic field such as an adsorbed dipole or screening of the image charge. It is proposed that the work function change originates from the perturbation of the conduction electron wave function by the Xe adatom as described for the effect of Xe in scanning tunneling microscopy.

Electronic structure and the martensitic transformation in beta -phase Ni-Al alloys: 27Al NMR and specific-heat measurements.

$^{27}\mathrm{Al}$ NMR line shape, Knight shift, relaxation rates together with low-temperature specific heat and magnetic susceptibiltiy were measured as a function of temperature and external magnetic-field in two Ni-rich \ensuremath{\beta}-phase Ni-Al alloys (62% Ni and 63% Ni) undergoing a martensitic phase transformation (MPT) below room temperature. For the purpose of comparison, two further alloys not undergoing the MPT were investigated (50% Ni and 55% Ni). Regarding the electronic properties of the alloys, we find an increase in the density of states at the Fermi level and a decrease of s-character of the conduction electron wave function as a function of the increase of Ni content from the 1:1 Ni-Al alloy. Furthermore, the inhomogeneous broadening of the $^{27}\mathrm{Al}$ linewidth indicates that the additional Ni replacing Al at the ``wrong'' site introduces quasilocalized magnetic states. Regarding the MPT we find a slight decrease of the Knight shift and of the Korringa product (${\mathit{T}}_{1}$T${)}^{\mathrm{\ensuremath{-}}1}$ going from the austenite to the martensite. In the transformation-temperature region, the $^{27}\mathrm{Al}$ NMR line is broadened by the effect of superposition of two signals arising from the austenite and the transforming phase. The deconvolution of the spectrum gives information about the nucleation and growth of the martensite, which appears to be continuous and involving a succession of intermediate states, in contrast with the abrupt nucleation of fully transformed martensite observed in Cu-Zn-Al. No anomalous enhancement of the relaxation rate is observed above ${\mathit{M}}_{\mathit{s}}$ or during the MPT. Although the NMR cannot rule out the presence of static precursor effects a few degrees above the transformation temperature ${\mathit{M}}_{\mathit{s}}$, no evidence was found for the formation of martensitic regions well above ${\mathit{M}}_{\mathit{s}}$ where tweed patterns are observed by electron microscopy.

Screening of the effect of delocalization on disordered transition metals by including the d states in the conduction band hybridization

The critical resistivity required for the temperature coefficient of electrical resistivity to change sign, for weakly disordered transition metals, may be larger than the Mooij universal boundary. A theoretical modification of the conduction electron wavefunction that involves including the d-state hybridization for the transition metals has a screening effect on the electron-phonon interaction and enhances the effect of localization on the inelastic scattering,.

The Knight shift and diffusion in solid lithium and sodium at pressures up to 8 GPa studied by NMR

The authors have measured the pressure dependence of the Knight shift and the linewidth of the nuclear magnetic resonance (NMR) signals of 7Li (up to 8 GPa) and 23Na (up to 6 GPa) in metallic lithium and sodium, respectively, at room temperature using a diamond anvil cell (DAC). It is concluded that diffusion is hindered by pressure; the diffusion coefficients and the activation volumes are estimated. In Li, diffusion increases at the BCC-FCC phase transition. The Li Knight shift increases with rising pressure up to the phase transition, where a marked reduction is observed which might be due to a drastic decrease of the s character of the conduction electron wave function. The Na shift decreases up to about 1.7 GPa and then increases. The Knight shift data are compared with theories that exist for pressures up to 1 GPa. By extrapolating existing values for the Pauli susceptibility, the pressure dependence of the spin density at the nuclear site is estimated.

Optically detected conduction electron spin resonance, overhauser shift and nuclear magnetic resonance in p-GaAlAs/GaAs heterostructures

The spin resonance of the conduction electrons in a single GaAlAs/GaAs heterostructure has been detected by measuring the degree of circular polarization of the luminescence in a microwave magnetic resonance field at 8.4 GHz. The effective g-factor is g ∗ = −0.47 ± 0.01, slightly different from the bulk value ≈ − 0.44. Additionally, the shift of the conduction electron spin resonance frequency due to the polarization of nuclei ( Overhauser shift ) has been observed for the first time in a single heterostructure. Additionally, the nuclear magnetic resonance can be observed directly by this very sensitive optical method because of the coupling of the nuclear spins to those of the conduction electrons. Lineshapes and intensities of the NMR signals depend on pumping light intensity and polarization. The measured relaxation rates of the different nuclei were found to be consistent with the results from the Overhauser shift. For the optical detection of both Overhauser shift and NMR, only nuclei which overlap with the wave function of conduction electrons near the GaAl-As/GaAs interface contribute to the measured signal.