Two Fermi Surface States and Two T_c-Rising Mechanisms Revealed by Transport Properties in RFeP_1-xAs_xO_0.9F_0.1 (R = La, Pr, and Nd)

Abstract

We demonstrate the relation between critical temperature T c and transport properties in RFeP 1Àx As x O 0:9 F 0:1 (R ¼ La, Pr, and Nd). T c and resistivity power-law exponent n form a universal line on the T c vs n plane for all the R-systems with x < 0:6{0:8, indicating that T c increases with bosonic fluctuation. Transport properties show anomalies suggesting a change of Fermi surfaces around x ¼ 0:6{0:8. Above x ¼ 0:6{0:8, T c and n approach the second T c -n line for the higher T c systems. A further increase of T c above x ¼ 0:6{0:8 indicates the presence of an additional T c -rising mechanism in this system.

The 3-Dimensional Fermi Liquid Description for the Iron-Based Superconductors

“…As described in the preceding paper [4], we have found that, for Ba(Fe 1−x Co x ) 2 As 2 , the ρ 1 /ρ 0 values have a close correlation with the superconducting transition temperature T C as a function of the doping content x. In the original BCS theory, the Cooper pair is formed between two quasiparticles whose momenta differ by 2 p 0 , while the logarithmic quasiparticle energy, 3 ln , arises mainly from the interactions of two quasiparticles whose momenta are almost equal or differ nearly by 2 p 0 ; thus, the strength and the nature of this interaction is closely connected with T Cvalues. It is frequently stated in the literature that the spin density fluctuations produce s +− -wave superconductivity [35,36], while the charge density (or orbital) fluctuations produce s ++ -wave superconductivity [37,38].…”

“…As shown in the figure, the data for the temperature range above the crystalline structural transition temperature, 75 K T 250 K, can be precisely fitted by Eq. (7.5) with q 1 = 1.28, 1.03 and 0.631 μV/K 2 , T 1 = 223, 233 and 263 K and T * Q = 479, 491 and 504 K; these q 1 values (the absolute value) are from 4 to 9 times larger than that of Pt, but about 1/30 of that of CeAl 3 .…”

“…Since χ(0), and hence K spin (0), is proportional to n 1/3 , on the crude assumption that (m * /m)/(1 + F a 0 ) is near to 1, from Eqs. (6.10), (6.11) and (6.12), we obtain n * /n = (0.0086/0.128) 3 [17], and solid lines are the theoretical fit to the data from Eq. (7.5) in the text.…”

“…Since the single particle excitations are not observed in the specific heat experiment, the superconductivity seems to be nodeless s +− -wave state. As has been discussed in 5., however, because this system is nearly ferromagnetic, we should carefully examine the possibility of the p-wave superconductivity similar to liquid He 3 and UPt 3 .…”

“…Concerning the nature of the normal state, however, the conclusions have not yet been settled. Many authors [1][2][3] in this field describe the system of quasiparticles as a non-Fermi liquid. The present author [4], however, states that the normal state of the substances can be described as a truly normal 3-dimensional (3D) Fermi liquid.…”