  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.

Strongly Correlated Electrons