# Single-Electron Bond in Ir–Ir Dimer Stabilized under Pressure

## TL;DR

A new material with a single-electron bond between iridium atoms is discovered, showing unique magnetic properties under high pressure.

## Contribution

The discovery of a single-electron bond in an Ir–Ir dimer and its stabilization under pressure in a new iridate compound.

## Key findings

- The Ir–Ir dimer in Ba3NbIr2O9 contains an unpaired electron, leading to electronic instability.
- Magnetic susceptibility and specific heat measurements show no long-range magnetic order down to 1.8 K.
- Electronic structure calculations suggest a homogeneous Ir3.5+–Ir3.5+ configuration in the dimer.

## Abstract

Odd-electron bonds, often considered ephemerally stable
in chemical
systems, can give rise to exotic physical phenomena in quantum materials.
In this study, we present the design and discovery of a new iridate,
Ba3NbIr2O9, which hosts a single-electron
bond within an Ir–Ir dimer. Ba3NbIr2O9 was synthesized under high-pressure and high-temperature
conditions and crystallizes in a hexagonal structure (space group P63/mmc). The Ir–Ir (III,
IV) dimer contains an unpaired electron, leading to an electronically
unstable state with potentially frustrated magnetic interactions.
Magnetic susceptibility measurements reveal a paramagnetic ground
state with no long-range magnetic order down to 1.8 K, despite a Curie–Weiss
temperature of −26.9 K. A sign of short-range magnetic ordering
is observed below 5 K. The specific heat measurements down to 1.8
K confirm that no long-range ordering is observed in Ba3NbIr2O9. Electronic structure calculations
indicate that the Ir–Ir dimer adopts a homogeneous Ir3.5+–Ir3.5+. These results highlight a novel design
strategy for quantum spin liquid candidates based on targeted manipulation
of chemical bonding environments.