Thermoelectric Power Anomaly of PrTi2Al20and PrV2Al20with Non-Kramers Γ3Ground State

Abstract

We investigated thermoelectric properties for PrTi2Al20 and PrV2Al20 below room temperature down to 0.13 K. A clear positive peak has been observed at 75 K 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 10 K owing to the CEF effect, and shows an additional tiny negative hump below 2 K as a signature of quadrupole ordering. On the other hand, \(S\) for PrV2Al20 manifests a large negative peak at 3 K with the magnitude of 3 μV/K. This gives a large enhancement in absolute \(S\) divided by temperature \(T\), \(|S|/T\), approximately below 10 K on cooling. \(|S|/T\) 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.