Jahn-Teller driven quadrupolar ordering and spin-orbital dimer formation in GaNb$_{4}$Se$_{8}$

Tsung-Han Yang; Tieyan Chang; Yu-Sheng Chen; K. W. Plumb

doi:10.1103/PhysRevB.109.144101

paper

Jahn-Teller driven quadrupolar ordering and spin-orbital dimer formation in GaNb $_{4}$ Se $_{8}$

arXiv:2401.04671 · doi:10.1103/PhysRevB.109.144101

Abstract

The lacunar spinel GaNb $_{4}$ Se $_{8}$ is a tetrahedral cluster Mott insulator where spin-orbit coupling on molecular orbitals and Jahn-Teller energy scales are competitive. GaNb $_{4}$ Se $_{8}$ undergoes a structural and anti-polar ordering transition at T $_{Q}$ = 50 K that corresponds to a quadrupolar ordering of molecular orbitals on Nb $_{4}$ clusters. A second transition occurs at T $_{M}$ = 29 K, where local distortions on the Nb $_{4}$ clusters rearrange. We present a single crystal x-ray diffraction investigation these phase transitions and solve the crystal structure in the intermediate T $_{M}$ < T < T $_{Q}$ and low T < T $_{M}$ temperature phases. The intermediate phase is a primitive cubic P2 $_{1}$ 3 structure with a staggered arrangement of Nb4 cluster distortions. A symmetry mode analysis reveals that the transition at TQ is continuous and described by a single Jahn-Teller active amplitude mode. In the low temperature phase, the symmetry of Nb $_{4}$ clusters is further reduced and the unit cell doubles into an orthorhombic P2 $_{1}$ 2 $_{1}$ 2 $_{1}$ space group. Nb $_{4}$ clusters rearrange through this transition to form a staggered arrangement of intercluster dimers, suggesting a valence bond solid magnetic state.

Jahn-Teller driven quadrupolar ordering and spin-orbital dimer formation in GaNb4​Se8​

Abstract

References in corpus (6)

Jahn-Teller driven quadrupolar ordering and spin-orbital dimer formation in GaNb $_{4}$ Se $_{8}$