Large anomalous Hall current induced by topological nodal lines in a ferromagnetic van der Waals semimetal

Abstract

Topological semimetals host electronic structures with several band-contact points or lines and are generally expected to exhibit strong topological responses. Up to now, most work has been limited to non-magnetic materials and the interplay between topology and magnetism in this class of quantum materials has been largely unexplored. Here we utilize theoretical calculations, magnetotransport and angle-resolved photoemission spectroscopy to propose FeGeTe, a van der Waals material, as a candidate ferromagnetic (FM) nodal line semimetal. We find that the spin degree of freedom is fully quenched by the large FM polarization, but the line degeneracy is protected by crystalline symmetries that connect two orbitals in adjacent layers. This orbital-driven nodal line is tunable by spin orientation due to spin-orbit coupling and produces a large Berry curvature, which leads to a large anomalous Hall current, angle and factor. These results demonstrate that FM topological semimetals hold significant potential for spin- and orbital-dependent electronic functionalities.

Large Anomalous Nernst Effect in a van der Waals Ferromagnet Fe3GeTe2

“…We have determined xx (defined as xx xx 2 + xy 2 ), and xy (-xy xx 2 + xy 2 ), the longitudinal and the transverse (or Hall) conductivities respectively, as well as xx (−∇ x /∇ x ) and yx (−∇ y /∇ x ), the longitudinal and the transverse Seebeck coefficients respectively. We have found very large AHE angle ( H = xy / xx ) and very large ANE angle ( N = yx / xx ), about 0.07 and 0.09 at low temperatures respectively, much larger than those found in common FM metals of 0.02 or less [12,[20][21][22][23]. This places FGT outside the realm of common FM materials.…”

“…Furthermore, the topological nature of FGT gives rise to some intriguing phenomena, for example, the observation of large anomalous Hall effect (AHE) [12] and magnetic skyrmions [13][14][15]. Of particular interest is the anomalous Nernst effect (ANE) in topological materials because the special band topology in these materials could introduce a very large ANE [16][17][18][19], which shares some similarities with, but also differences from, the better known AHE.…”

Spin and charge transport in topological nodal-line semimetals

“…But we note that our conclusions cannot be applied directly to these two Weyl NLS materials, because both of them have multiple nodal loops, resulting in elimination of the spin polarization of the transmitted current. We also note that in Weyl NLS ferromagnetic materials Li 3 (FeO 3 ) 2 [80] and Fe 3 GeTe 2 [81], the spin degree of freedom is fully quenched by the large ferromagnetic polarization and thus these two half -metallic materials can be viewed as spinless ones, indicating that they still cannot be served as the candidate materials.…”

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…Its perpendicular magnetic anisotropy (PMA) energy (~10 7 erg/cm 3 ) is almost two orders of magnitude larger than that of CrGeTe 3 (10 5 erg/cm 3 ), making it a better candidate for magnetic tunnel junctions and magnetic random access memory applications based on current‐induced switching . Besides, FGT exhibits many other intriguing properties, such as large anomalous Hall current driven by topological nodal lines . The spin degree of freedom is in this case fully quenched by the robust ferromagnetic polarization, while the line degeneracy is protected by crystalline symmetries connecting two orbitals in two adjacent layers.…”

“…85 Besides, FGT exhibits many other intriguing properties, such as large anomalous Hall current driven by topological nodal lines. 86 The spin degree of freedom is in this case fully quenched by the robust ferromagnetic polarization, while the line degeneracy is protected by crystalline symmetries connecting two orbitals in two adjacent layers. Strong electron correlation effects 87 and Kondo lattice 88 have also been evidenced, suggesting the presence of heavy fermions and periodically seated local moments.…”