Giant orbital diamagnetism of three-dimensional Dirac electrons in Sr₃PbO antiperovskite

Abstract

In Dirac semimetals, interband mixing has been known theoretically to give rise to a giant orbital diamagnetism when the Fermi level is close to the Dirac point. In Bi1-xSbx and other Dirac semimetals, an enhanced diamagnetism in the magnetic susceptibility χ has been observed and interpreted as a manifestation of such giant orbital diamagnetism. Experimentally proving their orbital origin, however, has remained challenging. The cubic antiperovskite Sr3PbO is a three-dimensional Dirac electron system and shows the giant diamagnetism in χ as in the other Dirac semimetals. Pb207 NMR measurements are conducted in this study to explore the microscopic origin of diamagnetism. From the analysis of the Knight shift K as a function of χ and the relaxation rate T1-1 for samples with different hole densities, the spin and the orbital components in K are successfully separated. The results establish that the enhanced diamagnetism in Sr3PbO originates from the orbital contribution of Dirac electrons, which is fully consistent with the theory of giant orbital diamagnetism.