Chirality Dependence of the KK-Momentum Dark Excitons in Carbon Nanotubes

Using a collection of twelve semiconducting carbon nanotube samples, each highly enriched in a single chirality, we study the chirality dependence of the $K$-momentum dark singlet exciton using phonon sideband optical spectroscopy. Measurements of bright absorptive and emissive sidebands of this finite momentum exciton identify its energy as 20 - 38 meV above the bright singlet exciton, a separation that exhibits systematic dependencies on tube diameter, $2n+m$ family, and semiconducting type. We present calculations that explain how chiral angle dependence in this energy separation relates to the Coulomb exchange interaction, and elaborate the dominance of the $K_{A_1'}$ phonon sidebands over the zone-center phonon sidebands over a wide range of chiralities. The Kataura plot arising from these data is qualitatively well described by theory, but the energy separation between the sidebands shows a larger chiral dependence than predicted. This latter observation may indicate a larger dispersion for the associated phonon near the $K$ point than expected from finite distance force modeling.Comment: 24 pages, 12 figures, 1 table; slight title change, Figures 1 and 11 added, reference added, presentation improved throughout documen

Static and Vibrational Properties of Equiatomic Cesium-Alkali Binary Alloys

The computations of the static and vibrational properties of four equiatomic Cs-based binary alloys viz. Cs0.5Li0.5, Cs0.5Na0.5, Cs0.5K0.5 and Cs0.5Rb0.5 to second order in local model potential is discussed in terms of real-space sum of Born von Karman central force constants. The local field correlation functions due to Hartree (H), Ichimaru-Utsumi (IU) and Sarkar et al. (S) are used to investigate influence of the screening effects on the aforesaid properties. Results for the lattice constants, i.e. С11, С12, С44, С12 – С44, С12 / С44, and bulk modulus B obtained using the H-local field correction function, have higher values in comparison with the results obtained for the same properties using IU and S local field correction functions. The results for the Shear modulus (C), deviation from Cauchy’s relation, Poisson’s ratio , Young modulus Y, propagation velocity of elastic waves, phonon dispersion curves and degree of anisotropy A are highly appreciable for the four equiatomic Cs-based binary alloys. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2779

Superconducting State Parameters of Binary Superconductors

A well known pseudopotential is used to investigate the superconducting state parameters viz. electron-phonon coupling strength , Coulomb pseudopotential *, transition temperature ТС, isotope effect exponent and effective interaction strength N0V for the AgxZn1 – x and AgxAl1 – x binary superconductors theoretically for the first time. We have incorporated here five different types of the local field correction functions to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange and correlation functions is concluded from the present study. The comparison with other such experimental values is encouraging, which confirms the applicability of the model potential in explaining the superconducting state parameters of binary mixture. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2777

Superconducting State Parameters of Bulk Amorphous Alloys

Well recognized empty core (EMC) pseudopotential of Ashcroft is used to investigate the superconducting state parameters viz; electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature TC, isotope effect exponent α and effective interaction strength NOV of some (Ni33Zr67)1 – xVx (x = 0, 0.05, 0.1, 0.15) bulk amorphous alloys. We have incorporated five different types of local field correction functions, proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange and correlation functions is concluded from the present study. The TC obtained from Sarkar et al. (S) local field correction function are found an excellent agreement with available theoretical data. Quadratic TC equation has been proposed, which provide successfully the TC values of bulk amorphous alloys under consideration. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the s bulk amorphous alloys. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3026

Računanje fononske disperzije u nekristalnim magnezijevim legurama

The computation of the phonon dispersion curves (PDC) and the related properties of three Mg-based metallic glasses, viz. Mg70Zn30, Mg84Ni16 and Mg85.5Cu14.5, are made using the well recognized model potential of Gajjar et al. The pseudo-alloy atom model is applied for the first time instead of the Vegard\u27s law. The three theoretical approaches given by Hubbard-Beeby, Takeno-Goda and Bhatia-Singh are used in the present study to compute the PDC of the systems. Five local-field correction functions proposed by Hartree, Taylor, Ichimaru-Utsumi, Farid et al. and Sarkar et al. are employed for the first time to see the effects of exchange and correlation. The thermodynamic and elastic properties are computed from the elastic limits of the PDC and found to be in qualitative agreement with the available theoretical or experimental data. The present findings for the PDC of Mg70Zn30 alloy are found in fair agreement with available theoretical and experimental data.Primjenom poznatog potencijala Gajjar-a i sur., izračunali smo fononske disperzijske funkcije (FDF) i fizička svojstva triju metalnih stakala na bazi magnezija, Mg70Zn30, Mg84Ni16 i Mg85.5Cu14.5. Prvi puta primjenjuje se model pseudo-leguraatom umjesto Vegardovog modela. Primijenili smo tri teorijska pristupa, HubbardBeeby-ev, Takeno-Goda-ov i Bhatia-Singh-ov za izračunavanje FDF. Radi nalaženja učinaka izmjene i korelacija, prvi smo uveli pet funkcija za popravke lokalnog polja, prema autorima Hartree-u, Taylor-u, Ichimaru-Utsumi-u, Farid-a i sur. te Sarkar-a i sur. radi nalaženja učinaka izmjene i korelacija. Izračunali smo termodinamička i elastična svojstva na osnovi elastične granice FDF i nalazimo dobar sklad s objavljenim teorijskim i eksperimentalnim podacima. Ishodi za FDF legure Mg70Zn30 su u razumnom skladu s teorijskim i eksperimentalnim podacima