Spin fluctuations and weak pseudogap behaviors in Na_{0.35}CoO_2:renomarization of band structure

TL;DR

This study investigates the electronic states of Na_{0.35}CoO_2 using a multi-orbital Hubbard model and FLEX approximation, revealing how Fermi surface topology influences pseudogap behaviors and quasiparticle mass enhancement, aligning with experimental observations.

Contribution

It demonstrates the impact of Fermi surface topology changes on pseudogap phenomena and quasiparticle properties in Na_{0.35}CoO_2, providing theoretical support for recent experiments.

Findings

Weak pseudogap behaviors observed in density of states and spin susceptibility.

Mass enhancement factor estimated as 1.5 to 1.8, consistent with ARPES data.

Fermi surface topology change linked to small hole pockets and trigonal distortion.

Abstract

We analyze the normal electronic states of Na$_{0.35}$CoO$_2$ based on the multi-orbital Hubbard model using the FLEX approximation. The fundamental electronic property of this system is drastically changed by the presence or absence of the small hole pockets associated with the $e_g'$ orbital. This change of the Fermi surface topology may be caused by the crystalline electric splitting due to the trigonal distortion. When small hole pockets are absent, the weak pseudogap bahaviors appear in the density of states and the uniform spin susceptibility, which are observed by recent experiments. We estimate the mass enhancement factor of quasiparticle $m^*/m\simeq 1.5\sim 1.8$. This result suppports recent ARPES measurements.