⁸Li NMR studies of Epitaxial Thin Films of the 3D topological Dirac semimetal Sr3SnO

The inverse perovskite Sr3SnO is a 3D cubic Dirac semimetal with a very small energy gap[1]. Its unusual electronic structure confers a variety of novel properties, such as chiral topological surface states, and very strong itinerant electron orbital magnetism. Remarkably, when doped it also becomes superconducting[2]. In the lowest carrier density samples, the Fermi level lies close to the Dirac points, and orbital magnetism is maximal. Here we report the results of ion-implanted Li-8(+) beta NMR in Au-capped epitaxial thin films of Sr3SnO as a function of carrier content. In addition, we stop the Li-8 in the Au overlayer to seek proximal evidence of the chiral surface state. In high magnetic field (6.55 T), we find remarkably little contrast in spin-lattice relaxation (SLR) between low carrier density Sr3SnO and the Au overlayer. In the inverse perovskite layer, 1/T-1 similar to 0:14 s(-1), slightly faster than Au at 300 K, while in the overlayer, there is a small but systematic enhancement in 1/T-1 compared to a control film of Au. The resonance in the Sr3SnO layer is broad with a long tail towards negative shift without resolved quadrupolar splitting.