Topological monopole's gauge field induced anomalous Hall effect in artificial honeycomb lattice

Abstract

Vortex magnetic structure in artificial honeycomb lattice provides a unique platform to explore emergent properties due to the additional Berry phase curvature imparted by chiral magnetization to circulating electrons via direct interaction. We argue that while the perpendicularly-aligned magnetic component leads to the quantized flux of monopole at the center of the Berry sphere, the in-plane vortex circulation of magnetization gives rise to unexpected non-trivial topological Berry phase due to the gauge field transformation. The unprecedented effect signifies the importance of vector potential in multiply-connected geometrical systems. Experimental confirmations to proposed hypotheses are obtained from Hall resistance measurements on permalloy honeycomb lattice. Investigation of the topological gauge transformation due to the in-plane chirality reveals anomalous quasi-oscillatory behavior in Hall resistance $R_{xy}$ as function of perpendicular field. The oscillatory nature of $R_{xy}$ is owed to the fluctuation in equilibrium current as a function of Fermi wave-vector $k_F$, envisaged under the proposed new formulation in this article. Our synergistic approach suggests that artificially tunable nanostructured material provides new vista to the exploration of topological phenomena of strong fundamental importance.