Many-Body Resonance in a Correlated Topological Kagome Antiferromagnet

We use scanning tunneling microscopy to elucidate the atomically resolved electronic structure in the strongly correlated kagome Weyl antiferromagnet ${\mathrm{Mn}}_3\mathrm{Sn}$. In stark contrast to its broad single-particle electronic structure, we observe a pronounced resonance with a Fano line shape at the Fermi level resembling the many-body Kondo resonance. We find that this resonance does not arise from the step edges or atomic impurities but the intrinsic kagome lattice. Moreover, the resonance is robust against the perturbation of a vector magnetic field, but broadens substantially with increasing temperature, signaling strongly interacting physics. We show that this resonance can be understood as the result of geometrical frustration and strong correlation based on the kagome lattice Hubbard model. Our results point to the emergent many-body resonance behavior in a topological kagome magnet.

Figure 1

(a) Crystal structure of the ${\mathrm{Mn}}_3\mathrm{Sn}$ kagome lattice. (b) $c$-axis $AB$ stacking of the kagome lattice from side view and top view, respectively. (c) Normalized bulk band structure of ${\mathrm{Mn}}_3\mathrm{Sn}$ in the conformal Brillouin zone showing low energy flatbands (black arrows) and Weyl nodes with two examples indicated by red and blue arrows. (d),(e) STM topographic images at different scales of ${\mathrm{Mn}}_3\mathrm{Sn}$ after annealing the cleaved surface at 1100 K for 1 h, showing a large atomic flat surface showing the lattice with hexagonal symmetry. (e) inset: First-principles simulation of the image overlaid with atoms illustrations. (f) STM topographic image across multiple steps of single layers, whose line profile is shown on the right. (g) Stacking alignment of two layers across a step, with the black and blue dots denoting Sn atoms of the upper and lower layers, respectively. All topographic data were taken at $T=4.6\mathrm{K}$, $V=-50\mathrm{mV}$, $I=50\mathrm{pA}$.

Figure 2

(a) $dI/dV$ line cut across 50 nm, taken far from any step edge, showing a peak at $E_F$. Every fifth curve is marked by a solid black line for clarity. (b) Perturbation of a step edge on the Fermi level resonance. The inset shows the line cut spectra taken across a single step edge, whose position is marked by the arrow. (c) Perturbation of the atomic impurity on the Fermi level resonance. The inset shows the topographic image of the impurity. (d) Spatially averaged $dI/dV$ spectrum (open circles). The solid line is a fit to Fano line shape function, $F(E)=[{(q+E/\mathrm{\Gamma })}^2]/[1+{(E/\mathrm{\Gamma })}^2]$.

Figure 3

(a) $dI/dV$ taken at 0 T (blue curve), 2 T along $a$ axis (brown curve), and 4 T along $c$ axis (yellow curve). (b) Temperature dependence of $dI/dV$ with spectra offset for clarity. The dotted lines are numerically calculated spectra by convoluting the 4.6 K data with the derivative of Fermi-Dirac distribution function at respective temperatures. (c) Fit of the temperature-dependent spectra by thermally convoluted Fano function. (d) Resonance width $\mathrm{\Gamma }$ plotted against temperature, giving a Kondo temperature of $T_K=30\mathrm{K}$ when fit to the Kondo model.

Figure 4

(a) Schematic depicting a Kondo lattice formed by the coupling between periodic localized states (red arrows) and itinerant conduction electrons (blue arrows). (b) DOS spectrum of the Kondo lattice, where a Kondo resonance (dark blue) at $E_F$ is generated by the many-body coupling of the localized flatband (red) and itinerant conduction band (shaded blue). (c) Band structure for a kagome tight-binding model showing a flatband with interband coupling and a large Hubbard interaction. (d) The calculated DOS shows a weak bump arising from the kagome flatband and a many-body resonance at $E_F$ due to the hybridization of the localized and itinerant states.