Molecular and Materials Science

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning: Mott insulators are materials that should conduct electricity under conventional band theories but are actually insulators due to electron–electron interactions. They have applications in thin-film magnetic heterostructures and high-temperature superconductivity. Published in Nature Communications (2016), the work presents µSR results from the CMMS combined with X-ray, neutron and µSR data from other laboratories in a study of metal-insulator transitions of prototypical Mott insulators. The composition of RENiO3 with various fractions of rare earths RE=La, Pr, Ni and Sm, provides a tuning parameter in the temperature-composition phase diagram, controlling a phase transition between an antiferromagnetic Mott insulating state and a paramagnetic metallic state, terminating in a quantum critical point at T=0. Being a sensitive probe of magnetism, µSR is the ideal tool to measure the magnetic field distribution, the magnetic volume fraction and excitations from the ordered magnetic ground state. This experiment produced evidence that the quantum phase transition (QPT) in RENiO3 is first order: the magnetically ordered volume fraction decreases continuously to zero at the QPT, while the ordered magnetic moment retains essentially its full value until it abruptly vanishes at the QPT. These results unambiguously demonstrate that the QPT in these materials proceeds in a distinctly first-order fashion. Studies of antiferromagnetic Mott insulators, as well as emergent quantum phenomena in other kinds of materials, are useful to elucidate both the system-specific and more universal roles of first-order behaviour in quantum phase evolution.