Doping-Driven Collapse of the SDW Correlation Gap in SmFeAsO$_{1-x}$F$_{x}$

TL;DR

This study investigates how doping affects the electronic properties and phase transitions in SmFeAsO$_{1-x}$F$_{x}$, revealing a collapse of the SDW gap and changes in carrier dynamics across different doping levels.

Contribution

It provides detailed measurements of Hall resistivity across doping levels, showing the doping-driven collapse of the SDW gap and the transition to Fermi-liquid behavior.

Findings

Highly doped samples show linear Hall resistivity with weak temperature dependence.

Lightly doped samples exhibit non-linear, temperature-dependent Hall resistivity near phase transitions.

The energy gap associated with the SDW phase decreases with increased doping.

Abstract

We report the Hall resistivity, $\rho_{xy}$ of polycrystalline SmFeAsO$_{1-x}$F$_{x}$ for four different fluorine concentrations from the onset of superconductivity through the collapse of the structural phase transition. For the two more highly-doped samples, $\rho_{xy}$ is linear in magnetic field up to 50 T with only weak temperature dependence, reminiscent of a simple Fermi liquid. For the lightly-doped samples with $x<0.15$, we find a low temperature regime characterized $\rho_{xy}(H)$ being both non-linear in magnetic field and strongly temperature dependent even though the Hall angle is small. The onset temperature for this non-linear regime is in the vicinity of the structural phase (SPT)/spin density wave (SDW) transitions. The temperature dependence of the Hall resistivity is consistent with a thermal activation of carriers across an energy gap. The evolution of the energy gap with doping is reported.