Fermi- to non-Fermi-liquid crossover and Kondo transition in two-dimensional Cu${}_{2\mathrm{/}3}$V${}_{1\mathrm{/}3}$V${}_2$S${}_4$

By means of a specific heat ($C$) and electrical resistivity ($\varrho$) study, we give evidence of a pronounced Fermi liquid (FL) behavior with sizable mass renormalization, $m^{\ast }\mathrm{/}m=30$, up to unusually high temperatures $\sim$70 K in the layered system Cu${}_{2\mathrm{/}3}$V${}_{1\mathrm{/}3}$V${}_2$S${}_4$. At low temperature, a marked upturn of both $C$ and $\varrho$ is suppressed by magnetic field, which suggests a picture of Kondo coupling between conduction electrons in the VS${}_2$ layers and impurity spins of the V${}^{3+}$ ions located between layers. This picture opens the possibility of controlling electronic correlations and the FL to non-FL crossover in simple layered materials. For instance, we envisage that the coupling between layers provided by the impurity spins may realize a two-channel Kondo state.