Uniaxial hybridization in the quasi-one-dimensional Kondo lattice CeCo2Ga8

We report the electron dynamics of the recently discovered quasi-one-dimensional Kondo lattice compound ${\mathrm{CeCo}}₂{\mathrm{Ga}}₈$ by optical spectra measurements using polarized light. For an electric field along the $c$ axis, the high-temperature Drude-like peak is found to split into two distinct components below the coherence temperature ${T}^*$, including a narrower Drude-like peak at low frequencies characterizing the emergent heavy electron state with a large mass enhancement, and a midinfrared Lorentz-like peak originating from interband transitions across the hybridization gap. The splitting is, however, absent for an electric field along the perpendicular directions, suggesting that the hybridization only occurs along the $c$ axis, although the high-temperature optical spectra from the background conduction electrons are isotropic. Our observations are in agreement with the resistivity data that show a broad maximum at around 20 K only along the $c$ axis but which keep increasing with a lowering temperature below 50 K along the $ab$ plane. Our work confirms the quasi-one-dimensional nature of the heavy electron physics in ${\mathrm{CeCo}}₂{\mathrm{Ga}}₈$ and establishes a direct correspondence between the bulk transport properties and microscopic electronic structures. It also pushes the previous observation of anisotropic coherence temperature in many heavy fermion compounds to an extreme situation and reveals the importance of intersite magnetic correlations beyond the local Kondo picture.