Angle-resolved photoemission spectroscopy of the Hund’s metal Sr₂MoO₄

The unconventional superconductor Sr₂RuO₄ has been investigated for decades, but questions about the nature of correlations in this material remain unanswered. In Sr₂RuO₄, four electrons are evenly distributed across the three t_2g orbitals, and it is believed that the strong correlations in Sr₂RuO₄ could be derived from interorbital Hund's interactions. However, the presence of a van Hove singularity near the chemical potential is a complicating factor. In Sr₂MoO₄ (4d²), the particle-hole analogue of Sr₂RuO₄ (4d⁴), the van Hove singularity is situated far above the chemical potential, allowing us to potentially probe spectral signatures of Hund's coupling via photoemission spectroscopy. Due to the inherent difficulties in stabilizing Mo in the 4d² configuration, virtually no experimental studies of Sr₂MoO₄ have been reported. Here, we synthesize Sr₂MoO₄ thin films with record-low residual resistivities via molecular beam epitaxy and use angle-resolved photoemission spectroscopy to measure the band-dependent quasiparticle mass enhancement, scattering rate, and Fermi liquid coherence as a function of energy and temperature. We compare these results to those from Sr₂RuO₄ and SrMoO₃ and discuss potential spectral signatures of Hund’s physics which are relevant for a broad class of materials.