Origin of charge density wave formation in insulators from a high resolution photoemission study of BaIrO3

We investigate the origin of charge density wave (CDW) formation in insulators by studying BaIrO3 using high-resolution (1.4 meV) photoemission spectroscopy. The spectra reveal the existence of localized density of states at the Fermi level, E(F), in the vicinity of room temperature. These localized states are found to vanish as the temperature is lowered, thereby, opening a soft gap at E(F), as a consequence of CDW transition. In addition, the energy dependence of the spectral density of states reveals the importance of magnetic interactions, rather than well-known Coulomb repulsion effect, in determining the electronic structure thereby implying a close relationship between ferromagnetism and CDW observed in this compound. Also, Ba core level spectra surprisingly exhibit an unusual behavior prior to CDW transition.     

Polarization of conduction electrons and hyperfine field on impurities in ferromagnetic metals

The temperature dependence of the polarization of conduction electrons and that of the magnetization are shown not to coincide in the presence of a sharp structure in the density of states in ferromagnetic metals. This effect can explain the experimentally observed temperature anomalies of the hyperfine field on impurities in ferromagnetic matrices.     

Areal density and spatial resolution of high energy electron radiography

Ultrafast imaging tools are of great importance for determining the dynamic density distribution in high energy density(HED) matter. In this work, we designed a high energy electron radiography(HEER) system based on a linear electron accelerator to evaluate its capability for imaging HED matter. 40 MeV electron beams were used to image an aluminum target to study the density resolution and spatial resolution of HEER. The results demonstrate a spatial resolution of tens of micrometers. The interaction of the beams with the target and the beam transport of the transmitted electrons are further simulated with EGS5 and PARMELA codes, with the results showing good agreement with the experimental resolution.Furthermore, the experiment can be improved by adding an aperture at the Fourier plane.     

Impurity band conduction in a high temperature ferromagnetic semiconductor

The band structure of a prototypical dilute magnetic semiconductor (DMS), Ga1-xMnxAs, is studied across the phase diagram via infrared and optical spectroscopy. We prove that the Fermi energy (EF) resides in a Mn-induced impurity band (IB). Specifically the changes in the frequency dependent optical conductivity [sigma1(omega)] with carrier density are only consistent with EF lying in an IB. Furthermore, the large effective mass (m*) of the carriers inferred from our analysis of sigma1(omega) supports this conclusion. Our findings demonstrate that the metal to insulator transition in this DMS is qualitatively different from other III-V semiconductors doped with nonmagnetic impurities. We also provide insights into the anomalous transport properties of Ga1-xMnxAs.     

NMR-analysis of the conduction electron polarization at the gadolinium site in ferromagnetic intermetallic compounds

We have studied the zero field spin echo NMR of ¹⁵⁵Gd, ¹⁵⁷Gd, ¹³⁹La, ¹⁹¹Ir and ¹⁹³Ir in the compounds Gd_xLa_1-x Ir₂ and Gd_xY_1-xIr₂. The ¹³⁹La resonance in particular proved useful as probe for the contribution (H_N) of the hyperfine field at the Gd site in GdIr₂ which is due to the polarizing influence of all the other Gd moments in the lattice. In GdIr₂ the contribution H_N was found to be positive; it is due for about 56% to the four nearest neighbour atoms. The part of H_N coming from the second and third nearest neighbour atoms has the same sign (positive) as that of the nearest neighbours. We show how the varying magnitude and sign of H_N in intermetallic compounds of Gd can be used to estimate the relative importance of 5d electrons in the indirect coupling of the localized rare-earth moments.     

Application of the Lucy-Richardson deconvolution procedure to high resolution photoemission spectra

Angle-resolved photoemission has developed into one of the leading probes of the electronic structure and associated dynamics of condensed matter systems. As with any experimental technique the ability to resolve features in the spectra is ultimately limited by the resolution of the instrumentation used in the measurement. Previously developed for sharpening astronomical images, the Lucy-Richardson deconvolution technique proves to be a useful tool for improving the photoemission spectra obtained in modern hemispherical electron spectrometers where the photoelectron spectrum is displayed as a 2D image in energy and momentum space.     

Interaction of spin waves with the conduction electron current and the ferromagnetic resonance linewidth in metals

It is shown that the interaction of spin waves with the conduction electron current does not lead to any new mechanism of linewidth broadening different from the well-known exchange-conductivitymechanism.     

Temperature-dependence of the angle-resolved photoemission in ferromagnetic transition metals

Temperature-dependence of the angle-resolved photoemission spectra in ferromagnetic metals is discussed in the light of a general picture of spin fluctuations. Calculations are made for Fe and Ni by using a local approach to the spin fluctuations and the results are compared with the recent calculation based on a long wave approximation.     

Evidence of electron fractionalization from photoemission spectra in the high temperature superconductors

In the normal state of the high temperature superconductors Bi(2)Sr(2)CaCu(2)O(8+delta) and La2(-x)Sr(x)CuO4, and in the related "stripe ordered" material, La(1.25)Nd(0.6)Sr(0.15)CuO4, there is sharp structure in the measured single hole spectral function, A<(k-->,omega), considered as a function of k--> at fixed small binding energy omega. At the same time, as a function of omega at fixed k--> on much of the putative Fermi surface, any structure in A<(k-->,omega), other than the Fermi cutoff, is very broad. This is characteristic of the situation in which there are no stable excitations with the quantum numbers of the electron, as is the case in the one-dimensional electron gas.     

High resolution study of the group V impurities absorption in silicon

High resolution spectra of P-, As- and Sb-doped Si have allowed the determination of the “natural” width of the impurity lines for concentration in the range of 10¹⁴ at cm^?3 and below. The width of the P-lines makes possible the observation of the 5p₀ line, very close to the 4p_± line. In the Sb- and As-doped samples, an effect similar to concentration broadening is observed. Results on P- and Bi-doped samples at lower resolution give evidence of the observation of the 3d₀(P) line and of internal Stark effect in the Bi-doped sample.     

Solubility and distribution of substitutional impurities in ferromagnetic alloys

We investigate the solubility of a magnetic substitutional impurity and its distribution over the sites of a face centered crystallographic lattice of an ordered A-B alloy of arbitrary composition, in which ferromagnetism can occur.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 66–72, June, 1986.     

Effects of temperature and impurities on electron radiation damage in the high voltage microscope

This paper describes the results of irradiation of specimens of copper and copper containing up to 2 at % beryllium in the high-voltage electron microscope. The results of irradiation at temperatures ranging from 20–500 K are described and discussed in the light of recently proposed theories of defect nucleation. Although the results are difficult to interpret because of the many diverse factors which influence the nucleation and growth of the damage it was found that the values for the volume density of defects were in general agreement with the predictions, if the effects of the foil surfaces were taken into account.

The corrected densities were used to derive values for the activation energy for motion of an interstitial in copper, E_m , and the binding energy between an interstitial and a beryllium atom, E_b . The results obtained were 0.12±0.03 eV for E_m and 0.29±0.07 eV for E_b .     

Fe impurities weaken the ferromagnetic behavior in Au nanoparticles

In this Letter, we report on a crucial experiment showing that magnetic impurities reduce the ferromagnetic order temperature in thiol-capped Au glyconanoparticles (GNPs). The spontaneous magnetization of AuFe GNPs exhibits a fast decrease with temperature that contrasts with the almost constant value of the magnetization observed in Au NPs. Moreover, hysteresis disappears below 300 K. Both features indicate that Fe impurities reduce the high local anisotropy field responsible for the ferromagnetic behavior in Au GNPs. As a consequence, the amazing ferromagnetism in Au NPs should not be associated with the presence of magnetic impurities.     

Nuclear spin-lattice relaxation of impurities in ferromagnetic iron

Due to the development of Green's function method the calculation of the nuclear spin-lattice relaxation time of impurities in ferromagnets has become feasible in the last years. We present the result of calculations for allsp andd impurities in ferromagnetic iron. The calculations are based on the density functional formalism. They well, reproduce the experimental trend of the relaxation timeT ₁ for bothsp andd impurities. By decomposing the relaxation rate into various contributions, we explain the observed systematic behavior ofT ₁ T in terms of the local electronic structure.     

Band effects on conduction electron density of states for the anderson model

Summary The effects of the shape of free conduction density of states on the physical quantities for the periodic Anderson model have been investigated.     

Localization of conduction electrons in the ferromagnetic clusters AuFe

The optical-conductivity spectra of concentrated solutions Au_{1 ? x} Fe _x with x = 17 and 22 at % have been measured in a frequency range of (10–33) × 10³ cm^?1 at room temperature. The results are analyzed together with previous optical data obtained for compounds with x = 4–12 at %. It is found that the magnetic contributions σ_magn = σ_AuFe ? σ_Au to dc and low-frequency(10 cm^?1) conductivities for an Fe concentration below 4 at % are almost equal, while the low-frequency magnetic contribution for larger concentrations is significantly larger than the dc one. An absorption band at frequencies of 1000–3000 cm^?1 has been found for samples with concentrations x = 6–22 at %. The observed phenomena are attributed to the localization of electrons inside clusters containing ferromagnetically ordered iron ions.     

Investigation of magnetic coupling at the interface of a ferromagnetic and paramagnetic metal by conduction electron spin resonance

Transmission conduction electron spin resonance through a sandwich of copper and permalloy layers show a spectrum indicative of a coupling between the magnetizations of the ferromagnetic and paramagnetic layers at the interface.     

Singular effects of impurities near the ferromagnetic quantum-critical point

Systematic theoretical results for the effects of a dilute concentration of magnetic impurities on the thermodynamic and transport properties in the region around the quantum critical point of a ferromagnetic transition are obtained. In the quasiclassical regime, the dynamical spin fluctuations enhance the Kondo temperature. This energy scale decreases rapidly in the quantum fluctuation regime, where the properties are those of a line of critical points of the multichannel Kondo problem with the number of channels increasing as the critical point is approached, except at unattainably low temperatures where a single channel wins out.