Manipulation of Dirac band curvature and momentum-dependent g factor in a kagome magnet YMn₆Sn₆

The Zeeman effect describes the energy change of an atomic quantum state in a magnetic field. The magnitude and the direction of this change depend on the dimensionless Lande g-factor. In quantum solids, the response of the Bloch electron states to the magnetic field also exhibits the Zeeman effect with an effective g-factor that was theoretically predicted to depend on the momentum, and which may be particularly strong in topological and magnetic systems. However, the momentum dependence of the g-factor is difficult to extract and it has not been directly measured. In this talk, we will discuss the experimental discovery of a momentum-dependent g-factor in the kagome magnet YMn₆Sn₆. We use spectroscopic-imaging scanning tunneling microscopy to map the evolution of a massive Dirac band in the vicinity of the Fermi level as a function of the magnetic field. We find that electronic states at different lattice momenta exhibit different Zeeman energy shifts, giving rise to an anomalous g-factor that peaks around the Dirac point. Our work provides a momentum-resolved visualization of Dirac band curvature manipulated by a magnetic field, which will be relevant to other topological kagome magnets.