Magnetic ground states and excitations in Zn-doped averieite -- a family of oxide-based $S=1/2$ kagome antiferromagnets

TL;DR

This study introduces a new oxide-based S=1/2 kagome antiferromagnet, Zn2-averievite, which exhibits a transition from magnetic order to a quantum spin liquid state with gapless excitations, providing a platform for exploring quantum criticality and doping in QSLs.

Contribution

First synthesis and characterization of Zn2-averievite, revealing a ground state evolution and a quantum spin liquid phase in a new oxide kagome antiferromagnet.

Findings

Zn2-averievite exhibits a quantum spin liquid state with gapless excitations.

Ground state transitions from magnetic order to spin-glass-like to QSL with increasing Zn content.

Dynamic susceptibility shows scaling behavior near a quantum critical point.

Abstract

Spin-1/2 kagome materials have recently attracted a resurgence of interest as they are considered an ideal host of the quantum spin liquid (QSL) state, which can underpin functionality such as superconductivity. Here we report the first synthesis and characterization of a new oxide-based distorted $S=1/2$ kagome antiferromagnet (KAFM) in the Zn$_x$Cu$_{5-x}$(VO$_4$)$_{2}$O$_2$CsCl (termed Zn$\mathbf {_x}$) series, namely Zn$_2$-averievite, Zn$\mathbf {_2}$ ($x=2$). Using magnetometry, synchrotron diffraction and neutron scattering we demonstrate an evolution of ground states with $x$ in Zn$\mathbf {_x}$; from long-range magnetic order in averievite ($x=0$), via a spin-glass-like ground state in Zn$\mathbf {_1}$, to a quantum spin liquid (QSL) in Zn$\mathbf {_2}$ for which inelastic neutron scattering reveals a gapless continuum of excitations. Similar to archetypal $S = 1/2$ KAFMs herbertsmithite and SrCr$_{8.19}$Ga$_{3.81}$O$_{19}$ (SCGO), the dynamic magnetic susceptibility of Zn$\mathbf {_2}$ shows scaling behavior consistent with proximity to a quantum critical point. The results demonstrate that the new Zn$\mathbf {_2}$ material is an excellent test bed for achieving the elusive goal of charge carrier doping in QSL states of $S = 1/2$ KAFMs, in-line with previous theoretical studies.