The ground state in a proximity to a possible Kitaev spin liquid: An undistorted honeycomb iridate NaxIrO3 (0.60 < x < 0.80)

TL;DR

This study investigates a newly synthesized honeycomb iridate NaxIrO3, revealing an undistorted lattice and exotic ground state features suggestive of proximity to a Kitaev spin liquid, with unique magnetic and thermal properties.

Contribution

It provides the first detailed characterization of NaxIrO3's structure and magnetic behavior, highlighting its potential as a platform near a Kitaev spin liquid state.

Findings

Undistorted honeycomb lattice without stacking disorder.

Absence of long-range magnetic order above 1 K.

Anomalies in heat capacity and susceptibility indicating exotic ground state.

Abstract

We report results of our study of a newly synthesized honeycomb iridate NaxIrO3 (0.60 < x < 0.80). Single-crystal NaxIrO3 adopts a honeycomb lattice noticeably without distortions and stacking disorder inherently existent in its sister compound Na2IrO3. The oxidation state of the Ir ion is a mixed valence state resulting from a majority Ir5+(5d4) ion and a minority Ir6+(5d3) ion. NaxIrO3 is a Mott insulator likely with a predominant pseudospin = 1 state. It exhibits an effective moment of 1.1 Bohr Magneton/Ir and a Curie-Weiss temperature of -19 K but with no discernable long-range order above 1 K. The physical behavior below 1 K features two prominent anomalies at Th = 0.9 K and Tl = 0.12 K in both the heat capacity and AC magnetic susceptibility. Intermediate between Th and Tl lies a pronounced temperature linearity of the heat capacity with a large slope of 77 mJ/mole K2, a feature expected for highly correlated metals but not at all for insulators. These results along with comparison drawn with the honeycomb lattices Na2IrO3 and (Na0.2Li0.8)2IrO3 point to an exotic ground state in a proximity to a possible Kitaev spin liquid.