Physical realization of a quantum spin liquid based on a novel frustration mechanism

TL;DR

This paper reports the experimental realization of a quantum spin liquid in Ca$_{10}$Cr$_7$O$_{28}$, a novel magnetic system with a unique frustration mechanism, showing coherent spin dynamics and no static magnetism.

Contribution

It introduces a new magnetic compound exhibiting quantum spin liquid behavior due to a previously unexplored frustration mechanism.

Findings

Displays features of a quantum spin liquid including coherent spin dynamics

Shows absence of static magnetism in the ground state

Demonstrates a novel frustration mechanism in a magnetic system

Abstract

Unlike conventional magnets where the magnetic moments are partially or completely static in the ground state, in a quantum spin liquid they remain in collective motion down to the lowest temperatures. The importance of this state is that it is coherent and highly entangled without breaking local symmetries. Such phenomena is usually sought in simple lattices where antiferromagnetic interactions and/or anisotropies that favor specific alignments of the magnetic moments are "frustrated" by lattice geometries incompatible with such order e.g. triangular structures. Despite an extensive search among such compounds, experimental realizations remain very few. Here we describe the investigation of a novel, unexplored magnetic system consisting of strong ferromagnetic and weaker antiferromagnetic isotropic interactions as realized by the compound Ca$_{10}$Cr$_7$O$_{28}$. Despite its exotic structure we show both experimentally and theoretically that it displays all the features expected of a quantum spin liquid including coherent spin dynamics in the ground state and the complete absence of static magnetism.