Floquet spin states in OLEDs

Abstract

Electron and hole spins in organic light-emitting diodes constitute prototypical two-level systems for the exploration of the ultrastrong-drive regime of light-matter interactions. Floquet solutions to the time-dependent Hamiltonian of pairs of electron and hole spins reveal that, under non-perturbative resonant drive, when spin-Rabi frequencies become comparable to the Larmor frequencies, hybrid light-matter states emerge that enable dipole-forbidden multi-quantum transitions at integer and fractional g-factors. To probe these phenomena experimentally, we develop an electrically detected magnetic-resonance experiment supporting oscillating driving fields comparable in amplitude to the static field defining the Zeeman splitting; and an organic semiconductor characterized by minimal local hyperfine fields allowing the non-perturbative light-matter interactions to be resolved. The experimental confirmation of the predicted Floquet states under strong-drive conditions demonstrates the presence of hybrid light-matter spin excitations at room temperature. These dressed states are insensitive to power broadening, display Bloch-Siegert-like shifts, and are suggestive of long spin coherence times, implying potential applicability for quantum sensing.

Measuring the Magnetic Field Amplitude of rf Radiation by the Quasistatic Magnetic Field Effect in Organic Light-Emitting Diodes

“…Finally, we stress that this ultralow field regime is particularly interesting for probing the exotic nonperturbative regimes of ultrastrong or even deep-strong drive, where the Rabi frequency of the spin system exceeds its Larmor frequency. Interesting physics, such as the spin-Dicke effect and photon-dressed spin states, emerge in this regime of resonantly driven spin transitions [33,[38][39][40]. With a quantitative understanding of EDMR spectra at ultralow frequencies, we expect to be able to identify signatures of deep-strong driving, which would otherwise require unphysically large B 1 field strengths [33].…”

“…While one would expect a suppression of the Zeeman resonance for B 1 B 0 in the high-field limit, this is not the case for very weak static external magnetic fields B 0 because of the isotropic hyperfine fields. These fields effectively tilt the total static field such that a nonzero component perpendicular to B 1 exists [19,33]. Careful quantitative analysis of this feature may indeed offer a route to identifying such low-frequency Zeeman resonances by subtraction of the quasistatic contribution, and could be of interest as a laboratory-based probe of models of biological magnetoreception at geomagnetic field strengths [34].…”

Photon correlations probe the quantized nature of light emission from optoelectronic materials

“…In such a case, superradiant behavior can show up in the form of spin-dependent charge transport, most notably in OLEDs. 65,66 Such spin-dependent transport may in turn influence excitonic fluorescence properties by charge-exciton interactions. 67…”

Line Shapes of Electric Dipole Spin Resonance in Pauli Spin Blockade

“…Altogether, we thus need to consider the effects on the spin blockade of (1) a periodic modulation of the on-site potentials combined with SOI and (2) an oscillating effective on-site magnetic field. Previous similar theoretical studies of EDSR in the spin-blockade regime focused on mechanism (i ) in the strong-driving limit [44,45,47] or on mechanism (ii ) in the absence of both SOI and coherent interdot coupling [48][49][50][51]. Other related studies focus on a lifting of the Pauli spin blockade in the presence of SOI and hyperfine coupling but without an external driving of the system [52,53].…”