Semimetallic Kondo lattice behavior in YbPdAs with a distorted kagome structure

We have synthesized YbPdAs with the hexagonal ZrNiAl-type structure in which the Yb atoms form a distorted kagome sublattice in the hexagonal-basal plane. Magnetic, transport, and thermodynamic measurements indicate that YbPdAs is a low-carrier Kondo lattice compound with an antiferromagnetic transition at TN = 6.6 K, which is slightly suppressed in applied magnetic fields up to 9 T. The magnetic entropy at TN recovers only 33% of Rln2, the full entropy of the ground-state doublet of the Yb-ions. The resistivity displays a -lnT dependence between 30 and 15 K, followed by a broad maximum at Tcoh = 12 K upon cooling. Below Tcoh, the magnetoresistance changes from negative to positive, suggesting a crossover from single-ion Kondo scattering processes at intermediate temperatures to coherent Kondo lattice behaviors at low temperatures. Both the Hall resistivity measurements and band-structure calculations indicate a relatively low carrier concentration in YbPdAs. Our results suggest that YbPdAs could provide an opportunity for examining the interplay of Kondo physics and magnetic frustration in low carrier systems.