# Persistent low-temperature spin dynamics in the mixed-valence iridate Ba$_{3}$InIr$_{2}$O$_{9}$

## TL;DR

This study provides evidence for a quantum spin-liquid state in Ba₃InIr₂O₉, characterized by persistent low-temperature spin dynamics, absence of magnetic order, and gapless excitations, driven by its unique mixed-valence and lattice geometry.

## Contribution

It reports the discovery of a putative quantum spin-liquid in a mixed-valence iridate with unique lattice geometry, combining multiple experimental techniques to characterize its dynamic, gapless ground state.

## Key findings

- No magnetic order or spin freezing down to 20 mK.
- Gapless ground state indicated by power-law behavior.
- Persistent spin dynamics over a wide temperature range.

## Abstract

Using thermodynamic measurements, neutron diffraction, nuclear magnetic resonance, and muon spin relaxation, we establish putative quantum spin-liquid behavior in Ba$_3$InIr$_2$O$_9$, where unpaired electrons are localized on mixed-valence Ir$_2$O$_9$ dimers with Ir$^{4.5+}$ ions. Despite the antiferromagnetic Curie-Weiss temperature on the order of 10 K, neither long-range magnetic order nor spin freezing are observed down to at least 20 mK, such that spins are short-range correlated and dynamic over nearly three decades in temperature. Quadratic power-law behavior of both the spin-lattice relaxation rate and specific heat indicates the gapless nature of the ground state. We envisage that this exotic behavior may be related to an unprecedented combination of the triangular and buckled honeycomb geometries of nearest-neighbor exchange couplings in the mixed-valence setting.