Interplay between strong correlations and electronic topology in the underlying kagome lattice of Na 2 / 3 Co O 2

Electronic topology in metallic kagome compounds is under intense scrutiny. We present transport experiments in ${\mathrm{Na}}_{2/3}\mathrm{Co}{\mathrm{O}}_{2}$ in which the Na order differentiates a Co kagome sublattice in the triangular $\mathrm{Co}{\mathrm{O}}_{2}$ layers. Hall and magnetoresistance (MR) data under high fields give evidence for the coexistence of light and heavy carriers. At low temperatures, the dominant light carrier conductivity at zero field is suppressed by a $B$-linear MR, suggesting Dirac-like quasiparticles. Lifshitz transitions induced at large $B$ and $T$ unveil the lower mobility carriers. They display a negative ${B}^{2}$ MR due to scattering from magnetic moments likely pertaining to a flat band. We emphasize an analogy with heavy fermion physics.