Change of Fermi surface states related with two different $T_{\mathrm{c}}$-raising mechanisms in iron pnictide superconductor

Abstract

Evolution of Fermi surface (FS) states of NdFeAs${}_{1-x}$P${}_x$O${}_{0.9}$F${}_{0.1}$ single crystals with As/P substitution has been investigated. The critical temperature $T_{\mathrm{c}}$ and the power law exponent ($n$) of temperature-dependent resistivity ($\rho (T)={\rho }_0+A{T}^n$) show a clear correlation above $x=$0.2, suggesting that $T_{\mathrm{c}}$ is enhanced with increasing bosonic fluctuation in the same type of FS state. Around $x=$0.2, all the transport properties show anomalies, indicating that $x$$\sim$0.2 is the critical composition of drastic FS change. The angle resolved photoemission spectroscopy has more directly revealed the distinct change of FS around $x=$0.2, that one hole FS disappears at Brillouin zone center and the other FS with propeller like shape appears at zone corner with decreasing $x$. These results are indicative of the existence of two types of FS state with different nesting conditions that are related with two $T_{\mathrm{c}}$-rising mechanisms in this system.

12 pages, 4 figures