Effect of intraband Coulomb repulsion on the excitonic spin-density wave

TL;DR

This study investigates how intraband Coulomb interactions influence the excitonic spin-density wave in a two-band model with nested Fermi surfaces, revealing robustness of the ESDW and significant effects on spin dynamics.

Contribution

It demonstrates the robustness of the excitonic spin-density wave against intraband interactions and analyzes their impact on spin susceptibility and spin-wave velocity.

Findings

ESDW state remains stable despite intraband Coulomb interactions

Intraband interactions significantly alter the paramagnon line shape

Spin-wave velocity is suppressed by intraband Coulomb repulsion

Abstract

We present a study of the magnetic ground state of a two-band model with nested electron and hole Fermi surfaces and both interband and intraband Coulomb interactions. Our aim is to understand how the excitonic spin-density-wave (ESDW) state induced by the interband Coulomb repulsion is affected by the intraband interactions. We first determine the magnetic instabilities of our model in an unbiased way by employing the random-phase approximation (RPA) to calculate the static spin susceptibility in the paramagnetic state. From this, we construct the mean-field phase diagram, demonstrating the robustness of the ESDW against the intraband interaction. We then calculate the RPA transverse spin susceptibility in the ESDW state and show that the intraband Coulomb repulsion significantly renormalizes the paramagnon line shape and suppresses the spin-wave velocity. We conclude with a discussion of the relevance of this suppression for the commensurate ESDW state of Mn-doped Cr alloys.