Magnetically ordered and kagome quantum spin liquid states in the Zn-doped claringbullite series

Neutron scattering measurements have been performed on deuterated powder samples of claringbullite and Zn-doped claringbullite (Zn${}_x$Cu${}_{4-x}$(OD)${}_6$FCl). At low temperatures, claringbullite Cu${}_4$(OD)${}_6$FCl forms a distorted pyrochlore lattice with long-range magnetic order and spin-wave-like magnetic excitations. Partial Zn doping leads to the nominal ZnCu${}_3$(OD)${}_6$FCl compound, a geometrically frustrated spin-1/2 kagome antiferromagnet that shows no transition to magnetic order down to 1.5 K. The magnetic excitations form a gapless continuum, a signature of fractional excitations in a quantum spin liquid.