Thermoelectric power anomaly of PrTi₂Al₂₀ and PrV₂Al₂₀ with non-kramers Γ₃ ground state

We investigated thermoelectric properties for PrTi2Al20 and PrV ₂Al₂₀ below room temperature down to 0.13 K. A clear positive peak has been observed at 75K in the thermoelectric power S for PrTi2Al20. Also for PrV₂Al₂₀, the similar S peak has been detected at 40 K. These peaks arise from the Kondo effect in the magnetic excited levels of the 4f -electronic state under a cubic crystalline electric field (CEF). In addition, for PrTi2Al20, S takes a minimum with a negative sign at 10K owing to the CEF effect, and shows an additional tiny negative hump below 2K as a signature of quadrupole ordering. On the other hand, S for PrV ₂Al₂₀ manifests a large negative peak at 3K with the magnitude of 3 μV/K. This gives a large enhancement in absolute S divided by temperature T, jSj=T , approximately below 10K on cooling. jSj=T reaches 4 μV/K₂ at 0.2 K, which is larger than that in the zero-T limit for a heavy-electron compound CeRu₂Si₂. This observation strongly indicates that the heavy-electron state brought by the quadrupolar Kondo effect is realized in the non-Kramers Γ₃ ground state of PrV₂Al₂₀.