Frustration-induced valence bond crystal and its melting in Mo3Sb7

TL;DR

This study uncovers a frustration-induced valence bond crystal in Mo3Sb7, where a transition to a nonmagnetic state involves lattice distortion and dynamic spin-singlet dimers, revealing complex magnetic and structural interplay.

Contribution

It demonstrates the existence of a frustration-induced valence bond crystal in Mo3Sb7 and elucidates its melting process involving lattice distortion and dynamic spin states.

Findings

Symmetry breaks to a nonmagnetic state below 50 K.

Lattice dynamics suggest a tetragonal distortion.

Valence bond crystal stabilized by frustration melts into a dynamic state.

Abstract

121/123Sb nuclear quadrupole resonance and muon spin relaxation experiments of Mo3Sb7 revealed symmetry breakdown to a nonmagnetic state below the transition recently found at TS=50 K. The transition is characterized by a distinct lattice dynamics suggested from narrowing of nuclear fields. We point out that the Mo sublatice is a unique three-dimensional frustrated lattice where nearest-neighbor and next-nearest-neighbor antiferromagnetic interactions compete, and propose that tetragonal distortion to release the frustration stabilizes long-range order of spin-singlet dimers, i.e., valence bond crystal, which is thermally excited to the dynamic state with cubic symmetry.