Comparative study on the thermoelectric effect of parent oxypnictides La$T$AsO ($T$ = Fe, Ni)

TL;DR

This study compares the thermoelectric effects in LaFeAsO and LaNiAsO, revealing significant differences linked to magnetic order and structural transitions, which may shed light on high-temperature superconductivity mechanisms.

Contribution

It provides a comparative analysis of thermopower and Nernst effects in parent oxypnictides, highlighting the role of spin-density wave order in LaFeAsO's anomalous behavior.

Findings

LaFeAsO exhibits larger thermopower and Nernst signals than LaNiAsO.

Abrupt changes in thermoelectric effects occur at structural and magnetic transition temperatures in LaFeAsO.

Nernst effect remains small and weakly temperature-dependent in LaNiAsO, similar to normal metals.

Abstract

The thermopower and Nernst effect were investigated for undoped parent compounds LaFeAsO and LaNiAsO. Both thermopower and Nernst signal in iron-based LaFeAsO are significantly larger than those in nickel-based LaNiAsO. Furthermore, abrupt changes in both thermopower and Nernst effect are observed below the structural phase transition temperature and spin-density wave (SDW) type antiferromagnetic (AFM) order temperature in Fe-based LaFeAsO. On the other hand, Nernst effect is very small in the Ni-based LaNiAsO and it is weakly temperature-dependent, reminiscent of the case in normal metals. We suggest that the effect of SDW order on the spin scattering rate should play an important role in the anomalous temperature dependence of Hall effect and Nernst effect in LaFeAsO. The contrast behavior between the LaFeAsO and LaNiAsO systems implies that the LaFeAsO system is fundamentally different from the LaNiAsO system and this may provide clues to the mechanism of high $T_c$ superconductivity in the Fe-based systems.