In-gap states and strain-tuned band convergence in layered structure trivalent iridate K0.75Na0.25IrO2

TL;DR

This study investigates the electronic structure of the less-explored trivalent iridate K0.75Na0.25IrO2, revealing in-gap states, strain-tunable band convergence, and potential for enhanced conductivity and thermoelectric applications.

Contribution

It provides a theoretical analysis of the electronic properties of K0.75Na0.25IrO2, highlighting the role of spin-orbit coupling and strain effects, which were previously underexplored in trivalent iridates.

Findings

In-gap states explain low activation energy.

Strain modulates band convergence and enhances conductivity.

SOC interactions lead to nonmagnetic Jeff=0 states.

Abstract

Iridium oxides (iridates) provide a good platform to study the delicate interplay between spin-orbit coupling (SOC) interactions, electron correlation effects, Hund's coupling and lattice degree of freedom. However, overwhelming investigations primarily focus on tetravalent (Ir4+, 5d5) and pentavalent (Ir5+, 5d4) iridates, far less attention has been paid to iridates with other valence states. Here, we pay our attention to a less-explored trivalent (Ir3+, 5d6) iridates, K0.75Na0.25IrO2, crystalizing in a triangular lattice with edge-sharing IrO6 octahedra and alkali metal ions intercalated [IrO2]- layers. We theoretically determine the preferred occupied positions of the alkali metal ions from energetic viewpoints and reproduce the experimentally observed semiconducting behavior and nonmagnetic (NM) properties. The SOC interactions play a critical role in the band dispersion, resulting in NM Jeff = 0 states. More intriguingly, our electronic structure not only uncovers the presence of in-gap states and explains the abnormal low activation energy in K0.75Na0.25IrO2, but also predicts the band edge can be effectively modulated by mechanical strain. Especially, the in-gap states feature with enhanced band-convergence characteristics by 6% compressive strain, which will greatly enhance the electrical conductivity of K0.75Na0.25IrO2. Present work sheds new lights on the unconventional electronic structures of the trivalent iridates, indicating its promising application as nanoelectronic and thermoelectric material.