Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy

TL;DR

This study uses angle-resolved photoemission spectroscopy to explore the electronic structure and quasiparticle behavior of Na0.7CoO2, revealing a small Fermi surface, narrow quasiparticle bands, and energy scales comparable to exchange interactions, which may influence its unusual properties.

Contribution

First detailed ARPES analysis of Na0.7CoO2 revealing key electronic features and energy scales relevant to its unconventional behavior.

Findings

Large hexagonal Fermi surface observed

Narrow, strongly renormalized quasiparticle bands

Estimated hopping parameter t ~ 8 meV, comparable to exchange coupling J

Abstract

We present an angle-resolved photoemission study of Na0.7CoO2, the host cobaltate of the NaxCoO2.yH2O series. Our results show a large hexagonal-like hole-type Fermi surface, an extremely narrow strongly renormalized quasiparticle band and a small Fermi velocity. Along the Gamma to M high symmetry line, the quasiparticle band crosses the Fermi level from M toward Gamma consistent with a negative sign of effective single-particle hopping (t ): t is estimated to be about 8 meV which is on the order of exchange coupling J in this system. This suggests that t ~ J ~ 10 meV is an important energy scale in the system. Quasiparticles are well defined only in the T-linear resistivity regime. Small single particle hopping and unconventional quasiparticle dynamics may have implications for understanding the unusual behavior of this new class of compounds.