Cotunneling spin blockade observed in a three-terminal triple quantum dot

We prepare a triple quantum dot with a separate contact lead to each dot to study Pauli spin blockade in the tunnel-coupled three dots in a row. We measure the tunneling current flowing between the center dot and either the left or right dot with the left and right leads as a common source and the center lead as a drain. In the biased stability diagram, we establish Pauli spin blockade in the respective neighboring dots, with features similarly obtained in double-quantum-dot systems. We further realize Pauli spin blockade with two different conditions by tuning the interdot coupling gates: strong and weak interdot tunnel coupling regimes. In the strong-coupling regime we observe significant suppression of cotunneling through the respective double dots due to Pauli spin blockade. We reveal the influence from the third dot in the triple-dot device on this cotunneling Pauli spin blockade and clarify that the cotunneling Pauli spin blockade is lifted by the resonant coupling of excited states to the third dot level as well as spin exchange of the left and right dots with the adjacent reservoir.