The influence of electron-phonon coupling and spin fluctuations on the superconductivity of the Ti-V alloys

Strong electron–phonon coupling and multiband effects in the superconductingβ-phase Mo1−xRexalloys

“…These phonon spectra are also in line with the α F 2 (ω) of the − Mo x 1 Re x alloys obtained from tunnelling experiments [20]. The average phonon frequency ω ln can be estimated from F(ω) as [37,43,44] ∫ ∫ ω ω ω ω Figure 7 shows the average phonon frequency ω ln expressed in Kelvin as a function of Re composition estimated from the F(ω) obtained from the temperature dependence of normal state heat capacity. The value of ω ln is about 250 K for Mo and decreases linearly with composition x except for a lateral shift at about x C2 =0.11.…”

“…The values of λe γ p for all the alloys do not match with λ sc ep. In the case of Mo, the value of λ sc ep is smaller than e γ p. We had observed similar behaviour in the Ti-V binary alloys as well, and pointed out that the spin fluctuations were responsible for such effect [35,37]. It is to be noted here that any possible influence of spin-fluctuations was not taken into account while estimating λe γ p in the present Mo1− xRex alloys.…”

“…This observation is further substantiated by the results of temperature dependent resistivity (presented latter in this paper) showing a very small contribution from the T 2 term, which rule out a predominant role of spin-fluctuations in this composition range. Furthermore, the results of our preliminary investigation of normal state dc magnetization do not reveal the typical signature of spin fluctuations as was observed in Ti-V alloys [35,37]. Tulina and Zaitsev pointed out from the point contact spectroscopy studies that the λ ep estimated from the phonon spectral function α F 2 (ω) alone cannot explain completely the enhancement of T C in the − Mo x…”

“…For Mo and the − Mo x 1 Re x alloys with x up to 0.05, the estimated T C is much higher than the experimentally obtained one. We had observed such differences in Ti-V alloys as well and we have attributed this to the presence of spin fluctuations in those alloys [35,37]. In the composition range 0.075-0.25, the experimental T C is higher than the estimated T C (shaded region in figure8), and the λ ep estimated from γ is smaller than that estimated from ΔC/γT C and T C .…”

“…It is to be noted here that any possible influence of spinfluctuations was not taken into account while estimating λ γ ep in the present − Mo x 1 Re x alloys. In the presence of spin-fluctuations, λ γ ep is renormalized by a factor (1 + λ sf ) −1 , where λ sf is electron spin-fluctuations coupling constant [35,37]. On the other hand while estimating λ sc ep using Δ γ C T C , the effect of spin-fluctuations is already taken in to account in the experimentally determined value of T C .…”