Condensation of holes into antiferromagnetic droplets in the organic semiconductor (DOEO)$_4$[HgBr$_4$]TCE

TL;DR

This study investigates the electronic and magnetic transformations in the organic semiconductor (DOEO)$_4$[HgBr$_4$]TCE, revealing charge localization, antiferromagnetic droplet formation, and surface electronic structure changes across temperature variations.

Contribution

It provides new insights into the formation of antiferromagnetic droplets and localized holes, combining microscopy, ESR, and photoelectron spectroscopy to analyze their properties.

Findings

Charge localization begins around 150 K.

Antiferromagnetic state appears below 60 K.

Detection of magnetic droplets and localized holes.

Abstract

Changes of the electronic structure accompanied by charge localization and a transition to an antiferromagnetic ground state were observed in the (DOEO)$_4$[HgBr$_4$]TCE organic semiconductor. Localization starts in the region of about 150 K and the antiferromagnetic state occurs below 60 K. The magnetic moment of the crystal contains contributions of antiferromagnetic inclusions (droplets), individual paramagnetic centers formed by localized holes and free charge carriers at 2 K. Two types of inclusions of 100-400 nm and 2-5 nm sizes were revealed by transmission electron microscopy. Studying the symmetry of the antiferromagnetic droplets (100-400 nm inclusions) and individual localized holes by electron spin resonance (ESR) revealed fingerprints of the antiferromagnetic resonance spectra of the spin correlated droplets as well as paramagnetic resonance spectra of the individual localized charge carriers. Photoelectron spectroscopy in the VUV, soft and hard X-ray range shows temperature-dependent effects upon crossing the critical temperature. The substantially different probing depths of soft and hard X-ray photoelectron spectroscopy yield information on the surface termination. The combined investigation using soft and hard X-ray photons to study the same sample results in details of electronic structure including structural aspects at the surface.