Spin resonance transport properties of a single Au atom in S–Au–S junction and Au–Au–Au junction

The spin transport properties of S–Au–S junction and Au–Au–Au junction between Au nanowires are investigated with density functional theory and the non-equilibrium Green's function. We mainly focus on the spin resonance transport properties of the center Au atom. The breaking of chemical bonds between anchor atoms and center Au atom significantly influences their spin transmission characteristics. We find the 0.8 eV orbital energy shift between anchor S atoms and the center Au atom can well protect the spin state stored in the S–Au–S junction and efficiently extract its spin state to the current by spin resonance mechanism, while the spin interaction of itinerant electrons and the valence electron of the center Au atom in the Au–Au–Au junction can extract the current spin information into the center Au atom. Fermi energy drift and bias-dependent spin filtering properties of the Au–Au–Au junction may transform information between distance, bias,and electron spin. Those unique properties make them potential candidates for a logical nanocircuit.     

Effect of Quantum Jumpers on the Critical Supercurrent in Dirty S–I–S Junctions

It has been shown that the presence of narrowband quantum jumpers in “dirty” (low concentrations of identical nonmagnetic impurities in the insulator (I) layer) S–I–S (S is a superconductor) junctions at the temperature T = 0 significantly reduces the critical supercurrent (Josephson current) as compared to the value given by the known the Ambegaokar–Baratoff relation. The performed estimates have shown the possibility of the experimental manifestation of this effect.     

Effect of replacement of Se by S on structural and physical properties of Ge–Sb–As–Se–S chalcogenide glasses

In the present study, the structural and opto-mechanical properties of Ge–Sb–As–Se–S chalcogenide glasses have been investigated. For this purpose, different bulk glasses of Ge₂₀Sb₅As₁₅Se_60?xS_x (0 ≤ x≤50) were prepared by conventional melt quenching technique in quartz ampoule and different characteristics of prepared glasses such as glass transition temperature, density, hardness, transmittance, optical band gap energy and refractive index were determined. The value of hardness and glass transition temperature of prepared glasses were found to increase with increasing the sulfur content as a result of formation of GeS₄ tetrahedral units and increasing the network connectivity and average bonding energy. The optical energy gap (according to Tauc’s relation), transmittance and refractive index of prepared glasses are in direct relation with sulfur content. In this study, the highest value of transmittance (about 70%) and lowest value of refractive index (2–2.3) was achieved in Ge₂₀Sb₅As₁₅Se₄₀S₂₀ and Ge₂₀Sb₅As₁₅Se₁₀S₅₀ glasses, respectively.     

Stability of Thin-Film Cu–As2S3 and Ag–As2S3 Structures

Technical Physics - Thin-film Cu–As2S3 and Ag–As2S3 structures obtained by successively evaporating Cu(Ag) and As2S3 in vacuum on glass substrates have been studied. Samples of these...     

Magnetic resonance in a gallium-doped Cu–Cr–S structure

A layered Cu–Cr–S structure doped with Ga ions and consisting of single-crystal CuCrS₂ layers, embedded with thin plates of spinel phases CuCr₂S₄ and CuGa_xCr_2–xS₄, has been studied using the magnetic resonance and magnetic susceptibility methods. The Curie temperature and the saturation magnetization of the spinel phases of the samples have been determined. The spinel phase layer thickness has been estimated.     

Positron trapping defects in free-volume investigation of Ge–Ga–S–CsCl glasses

Evolution of free-volume positron trapping defects caused by crystallization process in (80GeS₂–20Ga₂S₃)_100−х(СsCl)_x, 0 ≤ x ≤ 15 chalcogenide-chalcohalide glasses was studied by positron annihilation lifetime technique. It is established that CsCl additives in Ge–Ga–S glassy matrix transform defect-related component spectra, indicating that the agglomeration of free-volume voids occurs in initial and crystallized (80GeS₂–20Ga₂S₃)_100−х(СsCl)_x, 0 ≤ x ≤ 10 glasses. Void fragmentation in (80GeS₂–20Ga₂S₃)₈₅(СsCl)₁₅ glass can be associated with loosing of their inner structure. Full crystallization in each of these glasses corresponds to the formation of defect-related voids. These trends are confirmed by positron-positronium decomposition algorithm. It is shown, that CsCl additives result in white shift in the visible regions in transmission spectra. The γ-irradiation of 80GeS₂–20Ga₂S₃ base glass leads to slight long-wavelength shift of the fundamental optical absorption edge and decreasing of transmission speaks in favor of possible formation of additional defects in glasses and their darkening.     

Fabrication and temperature-dependent photoluminescence spectra of Zn–Cu–In–S quaternary nanocrystals

A series of Zn-Cu-In-S nanocrystals （ZCIS NCs） are prepared and the optical properties of the ZCIS NCs are tuned by adjusting the reaction time. It is interesting to observe that the temperature-dependent photoluminescence （PL） spectra of the ZCIS NCs show a redshift with decreasing intensity at low temperature （50-280 K） and a blueshift at high temperature （318--403 K）. The blueshift can be explained by the thermally active phonon-assisted tunneling from the excited states of the low-energy emission band to the excited states of the high-energy emission band.     

Energy Interval 1S–2S in Muonic Hydrogen and Helium

Journal of Experimental and Theoretical Physics - The interval of a large structure of energy spectrum (1S–2S) in muonic helium and hydrogen is calculated using a quasi-potential method in...     

Molecular dynamics simulation of sulphur nucleation in S–H2S system

The mechanism of sulphur nucleation in S–H₂S system is investigated by molecular dynamics simulation with the ReaxFF reactive force field. The results indicate that the nucleation of sulphur requires certain conditions. The nucleus of sulphur will form once the allotropes of sulphur dissolve from polysulphanes. Separate sulphur atoms aggregate into the cluster in the initial stage of nucleation according to the snowball effect. The cluster of nucleation is judged by the average distance of the neighbour sulphur atoms, which is identified as 2.8 Å through a parametric study. The sustainable process of nucleation depends on whether the cluster can overcome its critical state. The formation of the cluster may accelerate its own nucleation/coalescence and H₂S decomposition.     

Magnetic Parameters of Hg1–x Mn x Se1–y S y and Hg1–x Mn x Te1–y S y Crystals

The magnetic susceptibility of Hg_1–x Mn _x Se_1–y S _y and Hg_1–x Mn _x Te_1–y S _y crystals is investigated by the Faraday method at H = 3 kOe in the temperature interval T = 77–300 K. It is established that the specific features of are due to Mn–S–Mn–S, Mn–Se–Mn–Se, and Mn–Te–Mn–Te clusters and mixed Mn–Se–Mn–S and Mn–Te–Mn–S clusters of different sizes in which the indirect exchange antiferromagnetic interaction between Mn atoms is realized through chalcogen atoms. Based on the dependences 1/_Mn = f(T), the magnetic parameters are determined and their dependences on the crystal composition (x and y) are established.     

Optical frequency measurement of the 1S–3S two-photon transition in hydrogen

This article reports the first optical frequency measurement of the 1S–3S transition in hydrogen. The excitation of this transition occurs at a wavelength of 205 nm which is obtained with two frequency doubling stages of a titanium sapphire laser at 820 nm. Its frequency is measured with an optical frequency comb. The second-order Doppler effect is evaluated from the observation of the motional Stark effect due to a transverse magnetic field perpendicular to the atomic beam. The measured value of the 1S_1/21\mathrm{S}_{1/2}(F = 1)-3S_1/2(F = 1) frequency splitting is 2 922 742 936.729(13) MHz with a relative uncertainty of 4.5 × 10^-12. After the measurement of the 1S–2S frequency, this result is the most precise of the optical frequencies in hydrogen.     

A Dirac–Dunkl Equation on S2 and the Bannai–Ito Algebra

The Dirac–Dunkl operator on the two-sphere associated to the \({{\mathbb{Z}_{2}^{3}}}\) reflection group is considered. Its symmetries are found and are shown to generate the Bannai–Ito algebra. Representations of the Bannai–Ito algebra are constructed using ladder operators. Eigenfunctions of the spherical Dirac–Dunkl operator are obtained using a Cauchy–Kovalevskaia extension theorem. These eigenfunctions, which correspond to Dunkl monogenics, are seen to support finite-dimensional irreducible representations of the Bannai–Ito algebra.     

Pressure-Induced Metallization Accompanied by Elongated S–S Dimer in Charge Transfer Insulator NiS_2

The insulator-metal transition triggered by pressure in charge transfer insulator NiS2 is investigated by combining high-pressure electrical transport,synchrotron x-ray diffraction and Raman spectroscopy measurements up to40-50 GPa.Upon compression,we show that the metallization firstly appears in the low temperature region at～3.2 GPa and then extends to room temperature at～8.0 GPa.During the insulator-metal transition,the bond length of S-S dimer extracted from the synchrotron x-ray diffraction increases with pressure,which is supported by the observation of abnormal red-shift of the Raman modes between 3.2 and 7.1 GPa.Considering the decreasing bonding-antibonding splitting due to the expansion of S-S dimer,the charge gap between the S-ppπ* band and the upper Hubbard band of Ni-3 d eg state is remarkabl.y decreased.These results consistently indicate that the elongated S-S dimer plays a predominant role in the insulator-metal transition under high pressure,even though the p-d hybridization is enhanced simultaneously,in accordance with a scenario of charge-gap-controlled type.     

Some optical properties of Ge–S amorphous thin films

Amorphous Ge_xS_1−x films (x=0.27, 0.32, 0.36 and 0.4) were prepared by thermal evaporation. The values of the refractive index, the optical gap and the parameters of the Wemple–DiDomenico single oscillator model were determined. Using Miller's generalized rule the values of the third-order non-linear susceptibility were also estimated. Thermally induced bleaching was observed for films studied. Photobleaching was observed for sulfur rich and nearly stoichiometric films (x=0.27, 0.32) while for a germanium rich film (x=0.4) no response to the illumination was observed. The differences in photobleaching are attributed to the role of p-lone pair states and to an overall network rigidity of the films.     

The legacy of S Chandrasekhar (1910–1995)

Subrahmanyan Chandrasekhar, known simply as Chandra in the scientific world, is one of the foremost scientists of the 20th century. In celebrating his birth centenary, I present a biographical portrait of an extraordinary, but a highly private individual unknown to the world at large. Drawing upon his own “A Scientific Autobiography,” I reflect upon his legacy as a scientist and a great human being.     

Phase transitions in CuS–Ag2S nanoparticle system

(Ag₂)_xCu_1?xS, x = .2, .4, .6 and .8 nanoparticles were synthesized by the solvothermal method. The as-synthesized nanoparticles were characterized by X-ray diffraction to study the crystal structure and size. The surface morphologies of the above samples were studied using scanning electron microscope. As there is continuous shift in the lower wavelength absorption edge of the UV–VIS spectrum of these samples with concentration, (Ag₂)_xCu_1?xS nanoparticles can be tuned to different band gap energies by varying the composition. The D.C. electrical resistance was measured in the temperature range 310–485 K. As Ag₂S transforms from monoclinic to bcc at around 450 K, copper sulfide nanoparticles also shows a phase transition at around 470 K, the effects of these two transitions are seen in the resistance measurements and in the UV–VIS spectra of the entire system. The electrical resistance of (Ag₂)_xCu_1?xS nanoparticles rapidly reduces as more and more copper sulfide is added.     

Influence of the selenium content on thermo-mechanical and optical properties of Ge–Ga–Sb–S chalcogenide glasses

A number of Ge₁₇Ga₄Sb₁₀S_69−xSe_x (x = 0, 15, 30, 45, 60, and 69) chalcogenide glasses have been synthesized by a melt-quenching method to investigate the effect of the Se content on thermo-mechanical and optical properties of these glasses. While it was found that the glass transition temperature (T_g) decreases from 261 to 174 °C with increasing Se contents, crystallization temperature (T_c) peak only be observed in glasses with Se content of x = 45. It was evident from the measurements of structural and physical properties that changes of the glass network bring an apparent impact on the glass properties. Also, the substitution of Se for S in Ge–Ga–Sb glasses can significantly improve the thermal stability against crystallization and broaden the infrared transmission region.     

A Generic C1 Expanding Map¶has a Singular S–R–B Measure

We show that for a generic C¹ expanding map T of the unit circle, there is a unique equilibrium state for − log T′ that is an S–R–B measure for T, and whose statistical basin of attraction has Lebesgue measure 1. We also present some results related to the question of whether a generic C¹ expanding map preserves a σ-finite measure, absolutely continuous with respect to Lebesgue measure. Received: 8 December 2000 / Accepted: 27 March 2001