Continuous spin excitations in the three-dimensional frustrated magnet K2Ni2(SO4)3

TL;DR

This study reports the observation of continuous spin excitations in the 3D frustrated magnet K2Ni2(SO4)3, indicating quantum spin liquid features and introducing the 'hyper-trillium' lattice as a new frustrated quantum magnet platform.

Contribution

First experimental evidence of quantum spin liquid-like excitations in a 3D hyper-trillium lattice structure of K2Ni2(SO4)3.

Findings

Observation of a dominant excitation continuum in neutron scattering data.

Identification of key exchange interactions forming the hyper-trillium lattice.

Evidence of strong quantum spin fluctuations in the material.

Abstract

Continuous spin excitations are widely recognized as one of the hallmarks of novel spin states in quantum magnets, such as quantum spin liquids (QSLs). Here, we report the observation of such kind of excitations in K2Ni2(SO4)3, which consists of two sets of intersected spin-1 Ni2+ trillium lattices. Our inelastic neutron scattering measurement on single crystals clearly shows a dominant excitation continuum, which exhibits a distinct temperature-dependent behavior from that of spin waves, and is rooted in strong quantum spin fluctuations. Further using the self-consistent-gaussian-approximation method, we determined the fourth- and fifth-nearest neighbor exchange interactions are dominant. These two bonds together form a unique three-dimensional network of corner-sharing tetrahedra, which we name as ''hyper-trillium'' lattice. Our results provide direct evidence for the existence of QSL features in K2Ni2(SO4)3 and highlight the potential for the hyper-trillium lattice to host frustrated quantum magnetism.