Stable Unpaired Electron States in the Lu–LuBond Leading to the Absence of Odd–Even Parity in the KondoEffect of Lu₂@C₈₂ Transistors

Spin qubits constructed in endohedral fullerenes benefit from the protective shielding of the carbon cage, which effectively mitigates external decoherence and enables ultralong coherence times. However, endohedral fullerene spin qubits face the challenge of charge transfer in complex electrical environments, such as during qubit readout or large-scale integration, which can induce spin state modifications. In this study, we developed transistors based on the endohedral fullerene Lu₂@C₈₂ and observed the absence of parity dependence in the Kondo effect; this result was contradictory to the typical behavior of the Kondo effect observed in C₆₀. Density functional theory calculations revealed that upon electron loss, a spin-1/2 electron predominantly from the <i>s</i>-orbitals formed in the Lu–Lu bond and its orbital energy was significantly lower than that of the highest occupied molecular orbital. Based on these results, Lu₂@C₈₂ held stable unpaired electron states across multiple charge states and has potential applications in spin quantum devices.