Density of states in the impurity d band and inelastic electron scattering by a system of mixed-valence iron ions in HgSe: Fe crystals

The resistivity and the Hall coefficient of HgSe: Fe crystals with various iron content are experimentally studied in the temperature range 1.3≤T≤300 K and in magnetic fields up to 60 kOe. The temperature dependences of the density and mobility of conduction electrons in these crystals are determined. The influence of spatial charge ordering in the system of mixed-valence iron ions on impurity states in HgSe: Fe crystals is considered. The density of states in the impurity d band is theoretically analyzed, and inelastic electron scattering in which bi-and trivalent iron ions are recharged is discussed. It is shown that the experimentally detected features in the dependence of the density and mobility of electrons on temperature and iron impurity content can be explained by the influence of Coulomb correlations in the mixed-valence iron ion system on the structure of the impurity d band.

     

Temperature effect on spatial correlations of impurity ions in HgSe: Fe crystals

The spatial correlations in the arrangement of iron ions in HgSe: Fe compounds are described by the pair correlation function calculated within the hard sphere model. The temperature effect is taken into account by substituting the thermodynamic mean for the correlation sphere radius. The thermodynamic averaging is performed using the Einstein approach. The temperature dependences of the mobility of electrons scattered by a spatially correlated distribution of iron ions are calculated, and the results of these calculations are compared with the experimental data.     

Pair effects in the impurity band density of states

Results of a simple two center approximation for impurity bands are presented. For low concentrations the density of states deviates strongly from the single site CPA and agrees well with numerical “exact” results.     

Surface states in the conduction band region of Si

The energy distribution of surface states within the conduction band has been determined analizing the mobility ratio μ_H/μ_eff. A shallow trap model was used to describe the surface states.     

Bound states of an electron in an impurity potential on the surface of liquid helium

The energies and widths of the levels of an electron on impurity centers on the surface of liquid helium are calculated with allowance for the deformation of the surface. The level shift associated with the deformation effects is small and decreases very slowly with increasing level number. However, even a small shift of the energy levels relative to one another affects ripplon scattering, which makes the main contribution to the level width at low temperatures. It is predicted theoretically that this width depends very strongly on the external parameters and on the level number and that a maximum obtains at a clamping field E _⊥=51500 V/cm. The width of the levels of an electron in a bound state is found to be less than for free electrons. This makes it possible to perform a beautiful spectroscopic experiment. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 9, 599–604 (10 November 1997)     

HgSe:Fe—a mixed-valency system and the problem of the ground state

The dependence of the electron mobility on the iron impurity content N _Fe and temperature is studied for three variants of the ordering of Fe³⁺ ions in crystalline HgSe:Fe, a weakly correlated gas, states with near ordering like that in a strongly correlated Coulomb liquid, and long-range ordering. The electron mobilities owing to scattering on the correlated system of Fe³⁺ ions are determined. The temperature dependence of the mobility is analyzed for electron scattering on fluctuations in the charge density in a system of Fe²⁺-Fe³⁺ iron ions with mixed valency, and the correlation length is determined. It is shown that the ordering region for the Fe³⁺ ions encompasses only the first coordination sphere, i.e., near ordering in the position of the Fe³⁺ ions is established, as in a liquid. The coupling between the ordering of the Fe³⁺ ions and the formation of a correlation gap in the density of impurity d-states and its effect on the low-temperature behavior of the electron mobility in HgSe:Fe crystals are examined. Fiz. Tverd. Tela (St. Petersburg) 40, 425–432 (March 1998)     

Interaction of localized electronic states with the conduction band: band anticrossing in II-VI semiconductor ternaries

We report a strongly nonlinear pressure dependence of the band gaps and large downward shifts of the conduction band edges as functions of composition in ZnS xTe (1-x) and ZnSe (y)Te (1-y) alloys. The dependencies are explained by an interaction between localized A1 symmetry states of S or Se atoms and the extended states of the ZnTe matrix. These results, combined with previous studies of III-N-V materials define a new, broad class of semiconductor alloys in which the introduction of highly electronegative atoms leads to dramatic modifications of the conduction band structure. The modifications are well described by the recently introduced band anticrossing model.     

Theory of hopping conduction in two-dimensional impurity band under strong magnetic field

It is shown that the low-temperature conductivity in two-dimensional impurity band of n-type inversion layer under strong magnetic field is $\text{σ}{}_{\mathrm{xx}}\text{(}\text{min}\text{)=σ}{}_0\text{exp}\text{[?(}\text{T}{}_0\text{T}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{]}$. Therefore the effective conductivity of inversion layer $\text{σ}{}_{\mathrm{<mtext>eff</mtext>}}\text{=}\text{σ}{}^2{}_{\mathrm{xy}}\text{σ}{}_{\mathrm{xx}}\text{(}\text{min}\text{)}$ at Shubnikov-de Haas conductivity minima may be very high at low temperature.     

Concentration anomalies of the magnetization of HgSe:Fe crystals

The field and temperature dependences of the magnetization of the semimagnetic semiconductor HgSe:Fe have been studied experimentally. The spin splitting of the Landau levels in the de Haas-van Alphen quantum oscillations has been recorded in the iron impurity concentration interval of 7 × 10¹⁸ cm^?3 < N _Fe < 2 × 10¹⁹ cm^?3. The effective area of the extreme cross section of the Fermi surface has been determined from the obtained dependences of the oscillation period on the iron concentration, and the concentration of the collectivized electrons under conditions of the stabilization of the Fermi level on the iron donor level has been estimated. The critical impurity concentration at which the sharp increase in the Curie-Weiss temperature occurs owing to the spontaneous spin polarization of the system of hybridized electron states in iron-doped mercury selenide has been determined.     

Density of states in the conduction band of some rare earth oxides

The results of a systematic investigation of the intensity distribution near the short wavelength limit of the continuous X-ray spectrum for the most common rare earth oxides are reported. Anomalies in the band structure of some oxides have been observed and are discussed in terms of localized energy levels in the forbidden band due to the existence of colour centres. This implies that the physical properties of pure compounds strongly depend on the precise experimental conditions of preparation.     

On the cyclotron resonance width of an electron impurity system in two dimensions

Using the proper connected diagram expansion which incorporates the quasi-particle effect naturally we calculated the cyclotron resonance width γ in the extreme quantum limit.(a) γ ∝n

$\text{1}\text{2}$

_s B

$\text{1}\text{2}$

for a short range interaction, and (b) γ = π

$\text{1}\text{2}$

ze² κ^-1 <?crossed h.c.h;^-1 n

$\text{1}\text{2}$

_s for Coulomb interaction, are obtained. The field (B) and concentration (n_s)-dependence is in satisfactory agreement with experimental data. The variation γ = (γ²₁ + γ²₂ + …)

$\text{1}\text{2}$

of Matthiessen's rule γ = γ₁ + γ₂ + …, holds when there exist scattering centers of different kinds in the system.     

Pressure studies of charged donor superlattice in HgSe:Fe

Abstract

New mechanism of reduction of the scattering rate by charged impurities is investigated under hydrostatic pressure by means of classical and quantum transport. Also the critical pressures for the stuctural phase transitions in HgFeSe are determined.     

Binding energy between the magnetic impurity electron and the conduction electrons in the Anderson-Holstein model

A single-level Anderson-Holstein model is investigated using the Lang-Firsovtransformation followed by a zero-phonon averaging and the Kikuchi-Morita Clustervariation method as adopted by Bose and Tanaka in the case of Anderson model. The groundstate energy of the system at zero temperature and the binding energy between the magneticimpurity and the conduction electrons are calculated for the symmetric case ε _d = ?(U/2). Subsequently, the effect of the electron-phononinteraction on the ground state energy and the binding energy is investigated.     

Determination of observable conduction band symmetry in angle-resolved electron spectroscopies: Non-symmorphic space groups

In angle-resolved photoemission, selection rules restrict the observavle final state symmetry. The rules for the initial state in inverse photoemission are the same. For cubic groups they are known (Hermanson [1]). In non-symmorphic space groups new rules apply. Here we show how to determine the observable final states for this class of space groups and work out explicitly the example of the graphite structure. The mathematical concepts are supported by direct experimental evidence obtained in normal photoemission from graphite.     

Experimental evidence for electron channeling in Fe /Aau (100) superlattices.

We present transport and structural data from epitaxial (100) and (111) Au/Fe superlattices grown by molecular beam epitaxy. From their analysis, we conclude that an electron channeling mechanism, due to strong specular reflection of the minority spin carrier at the Au/Fe interfaces, is responsible for the high conductivity in the (100) superlattices.     

Attosecond electron delocalization in the conduction band through the phosphate backbone of genomic DNA

Partial density of states in the empty conduction band of the phosphate backbone sites in DNA was probed using energy-dependent resonant Auger spectroscopy. Results show that genomic DNA with periodic backbones exhibits an extended state despite separation of each phosphate group by an insulating sugar group. In antisense DNA with an aperiodic backbone, the equivalent state is localized. Remarkably rapid electron delocalization occurs at ca. 740 attoseconds for wet DNA, as estimated using the core-hole clock method. Such delocalization is comparable to the Fermi velocity of carbon nanotubes.