Detection of multiphoton magnetic dipole transitions using spin-dependent charge carrier recombination currents and an amplitude-modulated continuous wave electrically detected magnetic resonance scheme

We study nonlinear magnetic resonance phenomena such as the Bloch-Siegert shift and multiphoton magnetic dipole transitions [1] in the high-drive regime using electrically detected magnetic resonance (EDMR) spectroscopy of organic light emitting diodes with conductive polymers as active layers [2]. EDMR allows for the detection of magnetic resonance at very low magnetic fields, where spin-polarization is nearly non-existent. However, the measured spin-dependent electrical currents can be obscured by the superposition of randomly-occurring artifact signals induced by the spin-resonant radiation. Here, we demonstrate the use of an amplitude-modulated lock-in detection scheme that allows us to isolate these two electric current signatures, taking advantage of their different dynamic time scales. We show a significant improvement in signal-to-noise over unmodulated, direct detection of spin-dependent currents and observe the presence of two-photon magnetic dipole transitions [1]. [1] S. Jamali, V. V. Mkhitaryan, et al., arXiv:2010.02170; [2] S. Jamali et al., Nano Lett., 17, 4648 (2017).