While bulk 2H-NbSe2 is generally accepted to be a conventional superconductor, several unconventional features of the superconducting state have been reported in the monolayer limit, including the breaking of threefold symmetry in magnetotransport [1,2] and anomalously large in-plane critical fields . In this work, I will first present another unconventional feature measured by our collaborators : the existence of satellite peaks in the STM spectra of 1H-NbSe2 monolayers which exist only in the superconducting state and show a clear anticorrelation with the superconducting gap. After briefly discussing other potential candidate explanations, I will propose a scenario of competing pairing between s-wave and subleading f-wave triplet channels that leads to a superconducting Leggett collective mode. In particular, I will present a calculation of the Leggett mode energy using a simplified continuum model for NbSe2, and show that this particle-particle collective mode gives rise to resonances in the tunneling spectrum. I will discuss how our model compares with the experimental data, discuss the origin of the anticorrelation, and argue that it provides support to the competing pairing scenario, with a sizable attraction in the subleading triplet channel.
 A. Hamill, et al., Nat. Phys. 17, 949–954 (2021).
 C.-W. Cho, et al., arXiv:2003.12467 (2020).
 M. Kuzmanović, et al., arXiv:2104.00328 (2021).
 W. Wan, et al., arXiv:2101.04050 (2021).