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

TL;DR

This study investigates how Fermi surface states evolve in NdFeAs$_{1-x}$P$_x$O$_{0.9}$F$_{0.1}$ superconductors, revealing two distinct FS configurations linked to different mechanisms that enhance the critical temperature.

Contribution

It uncovers two different Fermi surface states associated with separate $T_c$-raising mechanisms in iron pnictide superconductors through combined transport and ARPES measurements.

Findings

Critical composition at $x\sim$0.2 marks a drastic FS change.

Two types of FS states with different nesting conditions identified.

$T_c$ correlates with bosonic fluctuations within the same FS state.

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 $T_{\rm c}$ and the power law exponent ($n$) of temperature-dependent resistivity ($\rho(T) = \rho_0 + AT^n$) show a clear correlation above $x=$0.2, suggesting that $T_{\rm c}$ 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 $T_{\rm c}$-rising mechanisms in this system.