FRG: Study of Pi-Conjugated Organic Semiconductors with Tailored Spin-Orbit Coupling

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Technical. This focused research group project is a collaborative effort among researchers with expertise in Organic Materials Science and Chemistry, Optics, Optoelectronics, Magneto-transport and Theoretical Physics. Intellectual Merit: The goals of the research are the synthesis, study of electronic and spin phenomena, and optoelectronic/spintronics applications of novel p-conjugated semiconductor systems that include heavy atoms such as platinum in their backbone structure, in order to tailor the spin-orbit coupling of the p-electron excitations. The increased spin-orbit (SO) coupling would enhance the singlet to triplet intersystem crossing, leading to a large triplet yield. It would also result in a strong phosphorescence (PH) emission band that is red-shifted with respect to the usual photoluminescence (PL) band. The large, tailored triplet yield would enable the study of high-density triplets, including their collective spin coherence properties for possible quantum manipulation of spin-qubits. The approach includes: (i) synthesis of Pt- and Ir- containing p- conjugated systems including monomers, polymers and co-polymers using new synthesis techniques, with control over the number of the heavy atoms in the backbone structure. (ii) measurement of optical and spin properties of singlet and triplet excitons, including ps time resolved response, the nature of the PH and PL emission bands, spin randomization of charge polarons, and spin coherence phenomena of triplet excitons using zero-field optically detected magnetic resonance (ODMR). (iii) study of collective spin coherence properties of triplets at high density via the manifestation of collective Rabi oscillations in the PH-ODMR where triplets are locked together via their mutual superradiance interaction coupling when applying a strong, resonant microwave radiation, and also by analyzing the PH noise spectrum. (iv) fabrication of spin organic light emitting diodes (S-OLED) with ferromagnetic spin-injecting electrodes and heavy-atom polymers, for studying the interplay of electro-PL and electro-PH emissions upon application of an external magnetic field to spin aligned carrier injection and transport. The theory team will support the research activity by providing highly necessary feedback to the experimentalists; this includes understanding of collective Rabi oscillations at high triplet density, Rabi oscillations nutation, analysis of PH emission noise, and a magneto-phonon resonance within the triplet spin sublevels. Non-Technical. Broader Impact: Research outcomes may include novel optoelectronic applications such as S-OLED and spin qubits for quantum computers. In addition the integration of experimental and theoretical efforts, including polymer synthesis, cw and ultrafast optics, magneto-transport, theoretical physics methods, and device fabrication, processing and testing, is expected to provide broad educational opportunities for graduate and undergraduate students.