Dependence of electron-spin Floquet states on drive polarization

Floquet theory predicts that in the nonperturbative regime of electron paramagnetic resonance (EPR), when the magnitude B₁ of the resonant drive field becomes similar to the static Zeeman field B₀, multiple dressed electron-spin states can emerge [1-3]. To experimentally test these predictions, we performed room-temperature strong-drive (B₁ > 1 mT, B₀ << 10 mT) EPR experiments, using electrically detected magnetic resonance (EDMR) spectroscopy of spin-dependent charge-carrier (polaron) currents in bipolar injection devices, essentially organic light-emitting diode (OLED) structures based on the perdeuterated π-conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Building on our previous work [4,5], we investigated the dependence of one-, two-, three-, and the previously unobserved four-photon transitions on the drive-field polarization, i.e. the angle θ between B₀ and B₁, at a drive frequency of 50 MHz. Our experiments show good agreement with predictions of Floquet theory of the strongly driven spin-pair dynamics.