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Estimation the Density of Localized State Glassy Se100–xZnx Thin Films by Using Space Charge Limited Conduction Measurement  [PDF]
Mohd. Nasir, M. Zulfequar
New Journal of Glass and Ceramics (NJGC) , 2012, DOI: 10.4236/njgc.2012.22013
Abstract: The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased of Zn concentration in the glassy alloys. The activation energy (ΔE) decreases with increase of Zn content. The conduction is explained on the basis of localized state in the mobility gap. To study the effect of electric field, a Current-Voltage characteristic has been measured at various fixed temperatures. The Current-Voltage data are fitted into the theory of space charge limited conduction in case of uniform distribution of traps in mobility gap at high electric fields (E ~104 V/cm) of these materials. The density of localized state (g0) are estimated by fitting in theory of space charge limited conduction (SCLC) at the temperature range of (352 - 372 K) in the glassy Se100–xZnx. The density of localized state (0) near the Fermi level are increases with increase of Zn concentration in the (Se100–xZnx) thin films and explain on the basis of increase of the Zn-Se bond.
Thermal and Optical Study of Te15(Se100-xBix)85 (x = 0, 1, 3) Chalcogenide Glasses  [PDF]
Kameshwar Kumar,Pankaj Sharma,S.S. Bhatt,Nagesh Thakur
Journal of Nano- and Electronic Physics , 2011,
Abstract: The present paper reports the thermal and optical study of Te15(Se100–xBix)85 (x = 0, 1, 3 at. %) glassy alloys. The glass transition temperature (Tg), crystalli-zation temperature (Tc) and melting temperature (Tm) are found from the DTA plots taken at different heating rates of 10, 15, 20 and 25 K/min. The glass transition temperature and melting temperature have been found to increase and the crystallization temperature has been found to decrease with increase in Bi content (x). Refractive index and optical energy gap of the films have been calculated from the transmission spectra taken in the spectral range 400-2300 nm. The refractive index decreases with wavelength and the optical band gap decreases with increase in Bi conten.
Dynamics of localized spins coupled to the conduction electrons with charge/spin currents  [PDF]
Masaru Onoda,Naoto Nagaosa
Physics , 2005, DOI: 10.1103/PhysRevLett.96.066603
Abstract: The effects of the charge/spin currents of conduction electrons on the dynamics of the localized spins are studied in terms of the perturbation in the exchange coupling $J_{K}$ between them. The equations of motion for the localized spins are derived exactly up to $O(J_{K}^2)$, and the equations for the two-spin system is solved numerically. It is found that the dynamics depends sensitively upon the relative magnitude of the charge and spin currents, i.e., it shows steady state, periodic motion, and even chaotic behavior. Extension to the multi-spin system and its implications including possible ``spin current detector'' are also discussed.
Anisotropic exchange interaction of localized conduction-band electrons in semiconductor structures  [PDF]
K. V. Kavokin
Physics , 2000, DOI: 10.1103/PhysRevB.64.075305
Abstract: The spin-orbit interaction in semiconductors is shown to result in an anisotropic contribution into the exchange Hamiltonian of a pair of localized conduction-band electrons. The anisotropic exchange interaction exists in semiconductor structures which are not symmetric with respect to spatial inversion, for instance in bulk zinc-blend semiconductors. The interaction has both symmetric and antisymmetric parts with respect to permutation of spin components. The antisymmetric (Dzyaloshinskii-Moriya) interaction is the strongest one. It contributes significantly into spin relaxation of localized electrons; in particular, it governs low-temperature spin relaxation in n-GaAs with the donor concentration near 10^16cm-3. The interaction must be allowed for in designing spintronic devices, especially spin-based quantum computers, where it may be a major source of decoherence and errors.
Determination of localized conduction band-tail states distribution in single phase undoped microcrystalline silicon  [PDF]
Sanjay K. Ram,Satyendra Kumar,P. Roca i Cabarrocas
Physics , 2007,
Abstract: We report on the phototransport properties of microstructurally well characterized plasma deposited highly crystallized microcrystalline silicon films. The steady state photoconductivity was measured on a wide microstructural variety of single-phase undoped microcrystalline silicon films as a function of temperature and light intensity. The band-tail parameter (kTc) was calculated from the photoconductivity light intensity exponent values at different temperatures for a range of quasi-Fermi energies. The localized tail states distribution in the vicinity of conduction band edge of microcrystalline silicon was estimated using the values of kTc. Our study shows that microcrystalline silicon films possessing dissimilar microstructural attributes exhibit different phototransport behaviors, which are linked to different features of the density of states maps of the material.
Conduction electrons localized by charged magneto-acceptors A$^{2-}$ in GaAs/GaAlAs quantum wells  [PDF]
M. Kubisa,K. Ryczko,I. Bisotto,C. Chaubet,A. Raymond,W. Zawadzki
Physics , 2015,
Abstract: A variational theory is presented of A$^{1-}$ and A$^{2-}$ centers, i.e. of a negative acceptor ion localizing one and two conduction electrons, respectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic field parallel to the growth direction. A combined effect of the well and magnetic field confines conduction electrons to the proximity of the ion, resulting in discrete repulsive energies above the corresponding Landau levels. The theory is motivated by our experimental magneto-transport results which indicate that, in a heterostructure doped in the GaAs well with Be acceptors, one observes a boil-off effect in which the conduction electrons in the crossed-field configuration are pushed by the Hall electric field from the delocalized Landau states to the localized acceptor states and cease to conduct. A detailed analysis of the transport data shows that, at high magnetic fields, there are almost no conducting electrons left in the sample. It is concluded that one negative acceptor ion localizes up to four conduction electrons.
Impact of cation-based localized electronic states on the conduction and valence band structure of AlInN alloys  [PDF]
S. Schulz,M. A. Caro,E. P. O'Reilly
Physics , 2013, DOI: 10.1063/1.4872317
Abstract: We demonstrate that cation-related localized states strongly perturb the band structure of $\text{Al}_{1-x}\text{In}_x$N leading to a strong band gap bowing at low In content. Our first-principles calculations show that In-related localized states are formed both in the conduction and the valence band in $\text{Al}_{1-x}\text{In}_x$N for low In composition, $x$, and that these localized states dominate the evolution of the band structure with increasing $x$. Therefore, the commonly used assumption of a single composition-independent bowing parameter breaks down when describing the evolution both of the conduction and of the valence band edge in $\text{Al}_{1-x}\text{In}_x$N.
Formation of Cooper pairs between conduction and localized electrons in heavy-fermion superconductors  [PDF]
Keisuke Masuda,Daisuke Yamamoto
Physics , 2012, DOI: 10.1103/PhysRevB.87.014516
Abstract: Cooper pairing between a conduction electron ($c$ electron) and an $f$ electron, referred to as the "$c$-$f$ pairing," is examined to explain s-wave superconductivity in heavy-fermion systems. We first apply the Schrieffer-Wolff transformation to the periodic Anderson model assuming deep $f$ level and strong Coulomb repulsion. The resulting effective Hamiltonian contains direct and spin-exchange interactions between $c$ and $f$ electrons, which are responsible for the formation of the $c$-$f$ Cooper pairs. The mean-field analysis shows that the fully gapped $c$-$f$ pairing phase with anisotropic s-wave symmetry appears in a large region of the phase diagram. We also find two different types of exotic $c$-$f$ pairing phases, the Fulde-Ferrell and breached pairing phases. The formation of the $c$-$f$ Cooper pairs is attributed to the fact that the strong Coulomb repulsion makes a quasiparticle $f$ band near the center of the conduction band.
The Effect of Diameter and Thermal Treatment on Magnetic Properties of Co1-xZnx Alloy Nanowires
Najafi M.,Rastegar Barmachi N.,Soltanian S.,Alemipour Z.
Proceedings of the International Conference Nanomaterials : Applications and Properties , 2012,
Abstract: Nanowire arrays of the alloy, Co1 xZnx (0 ≤ x ≤ 0.2), with 20 and 35 nm diameters have been fabricated by the electrochemical deposition method into pores of anodized aluminum oxide (AAO) templates. Samples with different composition could be obtained by adjusting the concentration ratio of Co2+ and Zn2+ in the solution of the electrolyte. The structure and magnetic properties were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and alternating gradient force magnetometer (AGFM). It is found that the magnetic properties of the arrays are critically dependent on the compositions and diameter and thermal treatments. We found that the optimized composition for Co1 xZnx nanowire is around Co90Zn10 with20 nm diameter annealed at 575 °C in which the coercivity (Hc=2120 Oe) and squareness (Mr/Ms=0.98) have their maximum values consistently.
Specific Heat-Coefficient of YbAl3 Studied by Combined Nearly Free Electron Conduction Band Hybridized with Localized f Electrons with Correlation Effect  [PDF]
Yoshiki Imai,Tetsuro Saso
Physics , 2009, DOI: 10.1143/JPSJ.78.064707
Abstract: Based on the recently proposed band model, the electronic specific heat of moderately heavy electron compound YbAl$_3$ are investigated. The band term of the Hamiltonian consists of three parts; conduction electrons described by the nearly free electron method, localized 4f electrons of Yb ions and the hybridization term between these electrons. Extracting several bands near the Fermi level, we reconstruct the low-energy effective Hamiltonian in order to consider the correlation effect, which is studied by using the self-consistent second order perturbation theory combined with local approximation. The temperature dependence of the specific heat $c_{\rm v}(T)$ is calculated as a function of temperature $T$ from the numerical derivative of the internal energy. Sommerfeld coefficient $\gamma$ is also calculated from the direct formula. The overall structure of $c_{\rm v}(T)/T$ is in quantitative agreement with the experimental results, which have the characteristic two-peak structures. They originate from the correlation effect and the structure of the non-interacting density of states, respectively. We show that our effective Hamiltonian yielding the realistic band structure may describe quantitatively heavy electron compounds with conduction bands composed of s- or p- electrons.
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