Spontaneous spin polarization in organic thiophene oligomers

•Charge induced spin polarization was found in organic semiconductors.•We consider spin–orbit coupling and spin-flip effect in our model.•Spin polarization exists only when injected charges reach a certain value.•Electron–phonon coupling is prerequisite for spin polarization.

We studied the spin polarization phenomenon of injected charges in organic thiophene oligomer by using extended Su–Schrieffer–Heeger (SSH) model including electron–electron interaction, spin–orbit coupling as well as spin-flip effect. Our simulation shows that a charged carrier is spontaneously spin polarized, which has a lower energy than the non-polarized one. This polarization is related with the amount of injected charges and the polymerization of the molecule.

Graphical abstractSpontaneous magnetic moment as a function of injected electron charges from 0 to 2e in thiophene from oligomer (T2) to polymer (T20). The inset shows the molecular structure of thiophene repeat unit.Figure optionsDownload full-size imageDownload as PowerPoint slide