Spin-orbit coupling and its effects in organic solids

• Published in: Physical review. B, Condensed matter and materials physics Vol. 85; no. 11
• Main Author: Yu, Z. G.
• Format: Journal Article
• Language: English
• Published: United States American Physical Society 02-03-2012
• Subjects: Aluminum; Condensed matter; Copper; COPPER PHTHALOCYANINE; Fluctuation; LIGANDS; Optical data processing; Orbitals; ORGANIC COMPOUNDS; Organic solids; Spin-orbit interactions
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.85.115201

We present a detailed analysis of spin-orbit coupling (SOC) in [pie]-conjugated organic materials and its effects on spin characteristics including the spin-relaxation time, spin-diffusion length, and g factor. While [pie] electrons are responsible for low-energy electrical and optical processes in [pie]-conjugated organic solids, [sigma] electrons must be explicitly included to properly describe the SOC. In particular, the g factor is not sensitive to the molecular geometry fluctuations, where the spin mixing within the same orbital is dominant. The SOCs in tris-(-8-hydroxyquinoline) aluminum (Alq[sub 3] ) and in copper phthalocyanine (CuPc) are particularly strong, due to the orthogonal arrangement of the three ligands in the former and Cu 3d orbitals in the latter. The theory quantitatively explains the recent measured spin-diffusion lengths in Alq[sub 3] from muon spin rotation and in CuPc from spin-polarized two-photon photo-emission.