Systematic Study on Fluorine-doping Dependence of Superconducting and Normal State Properties in LaFePO1-xFx

TL;DR

This study systematically examines how fluorine doping affects the structural, electronic, and superconducting properties of LaFePO, revealing weak doping dependence and suggesting electron doping has limited impact in this compound.

Contribution

It provides a detailed comparison of fluorine doping effects in LaFePO versus LaFeAsO, highlighting the weak influence of doping on LaFePO's properties.

Findings

F doping slightly decreases lattice parameter

Normal state resistivity shows T^2 dependence

System exhibits two-gap superconductivity

Abstract

We have investigated the fluorine-doping dependence of lattice constants, transports and specific heat for polycrystalline LaFePO1-xFx. F doping slightly and monotonically decreases the in-plane lattice parameter. In the normal state, electrical resistivity at low temperature is proportional to the square of temperature and the electronic specific heat coefficient has large value, indicating the existence of moderate electron-electron correlation in this system. Hall coefficient has large magnitude, and shows large temperature dependence, indicating the low carrier density and multiple carriers in this system. Temperature dependence of the upper critical field suggests that the system is a two gap superconductor. The F-doping dependence of these properties in this system are very weak, while in the FeAs system (LaFeAsO), the F doping induces the large changes in electronic properties. This difference is probably due to the different F-doping dependence of the lattice in these two systems. It has been revealed that a pure effect of electron doping on electronic properties is very weak in this Fe pnictide compound.