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

Abstract

The Zeeman effect describes the energy change of an atomic quantum state in magnetic field. The magnitude and the direction of this change depend on the dimensionless Landé 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 be dependent on the momentum. While typically negligible in many ordinary solids, the momentum-dependent variation of the g-factor is theorized to be substantially enhanced in many topological and magnetic systems. However, the momentum-dependence of the g-factor is notoriously difficult to extract and it is yet to be directly experimentally measured. In this work, we report the experimental discovery of a strongly momentumdependent g-factor in a kagome magnet YMn 6 Sn 6. Using spectroscopic-imaging scanning tunneling microscopy, we map the evolution of a massive Dirac band in the vicinity of the Fermi level as a function of magnetic field. We find that electronic states at different lattice momenta exhibit markedly different Zeeman energy shifts, giving rise to an anomalous g-factor that peaks around the Dirac point. Our work provides the first momentum-resolved visualization of Dirac band curvature manipulation by magnetic field, which should in principle be highly relevant to other topological kagome magnets.

Coherent magnetic and electronic structure symmetry broken in frustrated bilayer Kagome ferromagnet Fe3Sn2

“…Among these topological materials, magnetic Kagome materials are fascinating platforms to study the exotic physical properties due to their geometric frustration of crystal and magnetic structure [17], which is considered to be the root of many topological properties, like quantum spin liquid phase [18], flat band structure [19], Dirac or Weyl fermions [20][21][22], magnetic skyrmions [23], charge density wave [24][25][26] and so on. In Kagome materials, the SOC is also a key interaction to the topological properties [27,28], so they are ideal materials to study the influence of external magnetic field on electronic states, which has also been confirmed in some materials, like Fe 3 Sn 2 [29][30][31] and YMn 6 Sn 6 [32].…”

Quantum interactions in topological R166 kagome magnet

“…In an inplane magnetic field, the continuously varying spin structures may change the Fermi surface topology, causing a Lifshitz transition and a sharp reduction of the magnetoresistance up to 45% [148]. Under an out-of-plane magnetic field, STM experiments have also identified the manipulation of the massive Dirac cone near the Fermi level in YMn 6 Sn 6 [145]. By subtracting the band dispersions from quasiparticle interference (QPI) data, it was found that in addition to an overall Zeeman shift of the massive Dirac cone with increasing field, the band bottom of the Dirac cone is significantly rounded (figure 5(d)) due to a momentum-dependent g factor peaking around the Dirac point (figure 5(e)).…”

“…By subtracting the band dispersions from quasiparticle interference (QPI) data, it was found that in addition to an overall Zeeman shift of the massive Dirac cone with increasing field, the band bottom of the Dirac cone is significantly rounded (figure 5(d)) due to a momentum-dependent g factor peaking around the Dirac point (figure 5(e)). Several mechanisms have been proposed to explain this evolving factor, including the large orbital magnetic moments primarily localized near the Dirac points, the spin canting induced Dirac gap enhancing, as well as the evolving magnetic exchange coupling [145].…”

Plethora of tunable Weyl fermions in kagome magnet Fe3Sn2 thin films

“…Spectral peaks in STM dI/dV spectra of related materials have been typically associated with either Landau levels [35][36][37] , flat bands 28,38 , massive Dirac fermions 21 , and/or saddle points 39 . We deem that these are unlikely to explain the emergence and the evolution of spectral features in our work for the following reasons.…”