Abstract
In Dirac semimetals, inter-band mixing has been known theoretically to give rise to a giant orbital diamagnetism when the Fermi level is close to the Dirac point. In Bi$ _{1-x}$Sb$ _x$ and other Dirac semimetals, an enhanced diamagnetism in the magnetic susceptibility $\chi$ has been observed and interpreted as a manifestation of such giant orbital diamagnetism. Experimentally proving their orbital origin, however, has remained challenging. Cubic antiperovskite Sr$ _3$PbO is a three-dimensional Dirac electron system and shows the giant diamagnetism in $\chi$ as in the other Dirac semimetals. $ ^{207}$Pb 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 $\chi$ and the relaxation rate $T_1^{-1}$ 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 Sr$ _3$PbO originates from the orbital contribution of Dirac electrons, which is fully consistent with the theory of giant orbital diamagnetism.
Highlights
Dirac semimetals [1,2], whose band crossing is protected by the crystalline symmetry, have attracted considerable interest, largely because of the expected topological properties
The cubic antiperovskite Sr3PbO is a three-dimensional Dirac electron system and shows the giant diamagnetism in χ as in the other Dirac semimetals. 207Pb nuclear magnetic resonance (NMR) measurements are conducted in this study to explore the microscopic origin of diamagnetism
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
Summary
Dirac semimetals [1,2], whose band crossing is protected by the crystalline symmetry, have attracted considerable interest, largely because of the expected topological properties. The Berry curvature around the Dirac node gives rise to unconventional responses to magnetic fields such as a nontrivial phase shift in quantum oscillations [4,5] and a chiral anomaly [6,7]. The giant orbital diamagnetism of Dirac electrons [9,10] may be viewed as such an interband topological effect. This mechanism is distinct from the other kinds of magnetisms originating from itinerant electrons, Pauli paramagnetism and Landau diamagnetism, which are scaled by the density of states of itinerant electrons at the Fermi level
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