Low-temperature carrier transport of purely organic radicals embedded in double tunnel junctions*

Purely organic radicals hold promise for molecular spintronics because the molecules have weak spin-orbit coupling and the feature is expected to achieve long spin relaxation time [1]. In this work, we evaluated the carrier transport through stable oligo(p-phenylene ethynylene)-based radical molecules (TEMPO-OPE) at cryogenic temperature (<20 K). A striking point of our device is that molecules are embedded in insulating layer of a metal–oxide–silicon (MOS) structure, where the structure acts as a double-tunnel junction [2]. Obvious stepwise currents were observed in the current-voltage measurements. Furthermore, the peak positions in differential conductance curves were consistent with the molecular orbitals of the TEMPO-OPE. These results clarify that the molecules still keep their radical characters even in solid-state devices. Our proposed device therefore paves the way to realize new molecular spintronics devices with further prospect of the integration into current silicon device.
Reference: [1] R. Hayakawa et al. Nano Lett. 16, 4960 (2016). [2] R. Hayakawa et al. Nanoscale 9, 112897 (2017).