Solid State Phenomena Vol. 289

Abstract: Here we report on the results of our theoretical study of hydrogen localization and motion in disordered bcc Ti-V-Cr alloys. The calculations have been carried out within a DFT supercell approach for a certain composition, namely Ti_0.33V_0.27Cr_0.4 for H/M = 1/32. It was found that hydrogen is localized in highly distorted tetrahedral sites formed by different metal species. H atoms are displaced towards titanium. The estimation of the hydrogen diffusion parameters provides the activation energy value of 0.126 eV and the diffusion coefficient at 294 K equal to 1.9 10^-10 m/s² that is in good agreement with available experimental data.

Abstract: We consider the spin response within the five-orbital model for iron-based superconductors and study two cases: equal and unequal gaps in different bands. In the first case, the spin resonance peak in the superconducting state appears below the characteristic energy scale determined by the gap magnitude, 2Δ_L. In the second case, the energy scale corresponds to the sum of smaller and larger gap magnitudes, Δ_L+Δ_S. Increasing the values of the Hubbard interaction and the Hund's exchange, we observe a shift of the spin resonance energy to lower frequencies.