Change of Fermi surface states related with two different Tc -raising mechanisms in iron pnictide superconductors

Abstract

Evolution of Fermi surface (FS) states of NdFeAs1−xPxO0.9F0.1 single crystals with As/P substitution has been investigated. The critical temperature Tc and the power law exponent (n) of temperature-dependent resistivity (ρ(T ) = ρ0 + AT n ) show a clear correlation above x =0.2, suggesting that Tc 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∼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 Tc-rising mechanisms in this system.

Importance of $${{d}}_{{{xy}}}$$ orbital and electron correlation in iron-based superconductors revealed by phase diagram for 1111-system

“…There is another theoretical model for iron-based superconductors, shape resonance model 19 – 23 , where shows a clear enhancement around Lifshitz transition. In NdFeAs P (O,F), we observed the change of FS topology at Brillouin zone corner around –0.2, and that at zone center around –0.4 by angle-resolved photoemission spectroscopy measurement 13 , which may correspond to Lifshitz transition. However, the value changes gradually with x but does not show any abrupt change at a particular composition.…”

“…Our previous studies demonstrated that there is a critical change in the electronic state at around . This was evidenced not only by transport properties such as resistivity and Hall coefficient, but also by direct observation of the band structural change through the angle-resolved photoemission experiment 13 . We distinguish these two superconducting regions, naming the As-rich region “SC1” and the P-rich region “SC2”.…”