| Description |
This dissertation focuses on the exploration of nonlinear magnetic resonance effects that occur under the ultra-strong magnetic resonant drive of electron spin transitions when the ratio of the driving field amplitude (B1) and the static magnetic Zeeman field B0 are close to 1. The ultra-strong and deep strong (B1/B0 > 1) drive regimes of electronic transitions, both magnetic dipolar and electric dipolar transitions, have attracted a lot of attention in recent years, as observables revealing strong drive may be used as potential indicators for ultra-strong light-matter coupling effects that occur when electron/photon hybridization takes place. For the work presented in this dissertation, spin-dependent electron-hole polaron transitions in polymer-based bipolar injection devices (layer structures that are essentially equivalent to organic light-emitting diodes, OLEDs) were used as probes for room temperature electron spin resonance under very low Zeeman field conditions (~3 mT). Spin permutation symmetry-dependent charge carrier recombination rates in materials with weak spin-orbit coupling (which causes spin conservation) change in the presence of magnetic resonant drive. Thus, by measurement of these rates, e.g., through current measurements, magnetic resonance can be recorded in the near complete absence of spin polarization. This phenomenon, also known as electrically detected magnetic resonance (EDMR) has been exploited in this dissertation for the exploration of the ultra-strong drive regime through maximization of B1, which was accomplished through the integration of a microscopic device structure and a resonant radio-frequency (RF) source (a thin-film microwire) into a single monolithic thin-film layer stack. Using RF driving powers in the mW range, B1 of more than 2mT was demonstrated and a variety of strong magnetic resonance drive phenomena were observed, including the inversion of the EDMR current change due to spin-collectivity (the spin-Dicke effect) as well as the Bloch-Siegert-shift. The developed nanolayer device stack allowed for the demonstration of macroscopic spin collectivity that emerges in polymer devices at room temperature. The work presented indicates that the strong drive effects could potentially serve as an indicator for ultra-strong light-matter coupling experiments in which the paramagnetic polaron states of charge carriers in polymers would serve as two-level spin quantum systems (Qubits). |
