# Quantum magnetisms in uniform triangular lattices Li2AMo3O8 (A = In, Sc)

## TL;DR

This study investigates the magnetic ground states of two molecular triangular lattice compounds, revealing a conventional order in one and a quantum spin liquid-like state in the other, using muon spin rotation and neutron scattering techniques.

## Contribution

It provides the first detailed comparison of magnetic behaviors in Li$_2$InMo$_3$O$_8$ and Li$_2$ScMo$_3$O$_8$, highlighting how structural and interaction anisotropies influence their ground states.

## Key findings

- Li$_2$InMo$_3$O$_8$ shows 120° magnetic order with spin wave excitations.
- Li$_2$ScMo$_3$O$_8$ exhibits short-range order and quantum fluctuations.
- Different ground states are linked to structural and magnetic interaction anisotropies.

## Abstract

Molecular based spin-1/2 triangular lattice systems such as LiZn$_2$Mo$_3$O$_8$ have attracted research interest. Distortions, defects, and intersite disorder are suppressed in such molecular-based magnets, and intrinsic geometrical frustration gives rise to unconventional and unexpected ground states. Li$_2$$A$Mo$_3$O$_8$ ($A$ = In or Sc) is such a compound where spin-1/2 Mo$_3$O$_{13}$ clusters in place of Mo ions form the uniform triangular lattice. Their ground states are different according to the $A$ site. Li$_2$InMo$_3$O$_8$ undergoes conventional $120^\circ$ long-range magnetic order below $T_\text{N}=12$~K whereas isomorphic Li$_2$ScMo$_3$O$_8$ exhibits no long-range magnetic order down to 0.5~K. Here, we report exotic magnetisms in Li$_2$InMo$_3$O$_8$ and Li$_2$ScMo$_3$O$_8$ investigated by muon spin rotation ($\mu$SR) and inelastic neutron scattering (INS) spectroscopies using polycrystalline samples. Li$_2$InMo$_3$O$_8$ and Li$_2$ScMo$_3$O$_8$ show completely different behaviors observed in both $\mu$SR and INS measurements, representing their different ground states. Li$_2$InMo$_3$O$_8$ exhibits spin wave excitation which is quantitatively described by the nearest neighbor anisotropic Heisenberg model based on the $120^\circ$ spin structure. In contrast, Li$_2$ScMo$_3$O$_8$ undergoes short-range magnetic order below 4~K with quantum-spin-liquid-like magnetic fluctuations down to the base temperature. Origin of the different ground states is discussed in terms of anisotropies of crystal structures and magnetic interactions.