Quasimolecular $J_{\rm tet}$=3/2 moments in the cluster Mott insulator GaTa$_4$Se$_8$

TL;DR

This study uses resonant inelastic x-ray scattering to demonstrate that electrons in GaTa$_4$Se$_8$ form quasimolecular $J_{tet}=3/2$ moments, revealing how intracluster hopping influences the wavefunction and magnetic interactions in cluster Mott insulators.

Contribution

It provides direct experimental evidence of quasimolecular $J_{tet}=3/2$ moments in GaTa$_4$Se$_8$ and elucidates how intracluster hopping modulates the wavefunction and magnetic properties.

Findings

Electrons are delocalized over Ta$_4$ tetrahedra forming $J_{tet}=3/2$ moments.

The cluster wavefunction depends on competing intracluster hopping terms.

The wavefunction influences intercluster interactions and effective spin-orbit coupling.

Abstract

Quasimolecular orbitals in cluster Mott insulators provide a route to tailor exchange interactions, which may yield novel quantum phases of matter. We demonstrate the cluster Mott character of the lacunar spinel GaTa$_4$Se$_8$ using resonant inelastic x-ray scattering (RIXS) at the Ta $L_3$ edge. Electrons are fully delocalized over Ta$_4$ tetrahedra, forming quasimolecular $J_{\rm tet}$=3/2 moments. The modulation of the RIXS intensity as function of the transferred momentum q allows us to determine the cluster wavefunction, which depends on competing intracluster hopping terms that mix states with different character. This mixed wavefunction is decisive for the macroscopic properties since it affects intercluster hopping and exchange interactions and furthermore renormalizes the effective spin-orbit coupling constant. The versatile wavefunction, tunable via intracluster hopping, opens a new perspective on the large family of lacunar spinels and cluster Mott insulators in general.