In-plane anisotropy of transport coefficients in the electronic nematic states: Universal origin of the nematicity in Fe-based superconductors

TL;DR

This paper investigates the in-plane anisotropy of transport coefficients in Fe-based superconductors, revealing a universal origin of nematicity linked to orbital-dependent scattering and Fermi surface differences.

Contribution

It introduces a unified explanation for the material-dependent anisotropy in resistivity and thermoelectric power in nematic states of Fe-based superconductors.

Findings

Resistivity anisotropy varies with material, with FeSe showing $ ho_x> ho_y$ and others showing $ ho_x< ho_y$.

Differences in hole-pocket numbers explain the anisotropy reversal.

Orbital-dependent scattering underpins the universal origin of nematicity.

Abstract

The origin of the electronic nematicity and its remarkable material-dependence are famous longstanding unsolved issues in Fe-based superconductors. To attack these issues, we focus on the in-plane anisotropy of the resistivity: In the nematic state in FeSe, the relation $\rho_x>\rho_y$ holds, where $\rho_{x(y)}$ is the resistivity along the longer (shorter) Fe-Fe axis. In contrast, the opposite anisotropy $\rho_x<\rho_y$ is realized in other undoped Fe-based superconductors. Such nontrivial material dependence is naturally explained in terms of the strongly orbital-dependent inelastic quasiparticle scattering realized in the orbital-ordered state. The opposite anisotropy between FeSe ($\rho_x>\rho_y$) and other undoped compounds ($\rho_x<\rho_y$) reflects the difference in the number of hole-pockets. We also explain the large in-plane anisotropy of the thermoelectric power in the nematic state.