Holes in a quantum spin liquid

Magnetic neutron scattering provides evidence for nucleation of antiferroma gnetic droplets around impurities in a doped nickel oxide-based quantum mag net. The undoped parent compound contains a spin Liquid with a cooperative singlet ground state and a gap in the magnetic excitation spectrum. Calcium doping creates excitations below the gap with an incommensurate structure factor. We show that weakly interacting antiferromagnetic droplets with a c entral phase shift of pi and a size controlled by the correlation Length of the quantum Liquid can account for the data. The experiment provides a qua ntitative impression of the magnetic polarization cloud associated with hol es in a doped transition metal oxide.