Title: Spin-orbit coupling in organic spintronics

Guest Speaker: Zhi-Gang Yu

Time: 2015-1-19 (Monday), 10:00-11:30

Location: Conference Room (7205), School of Science

Abstract

I will talk about spin-orbit coupling (SOC) in p-conjugated organic materials and its effects on spin characteristics including the spin-relaxation time, spin-diffusion length, and g factor. While p electrons are responsible for low-energy electrical and optical processes in p-conjugated organic solids, s electrons must be explicitly included to properly describe the SOC. The SOC mixes up- and down-spin states and, in the context of spintronics, can be quantified by an admixture parameter in the electron and hole polaron states in p-conjugated organics. Molecular geometry fluctuations such as ring torsion, which are common in soft organic materials and may depend on sample preparation, are found to have a strong effect on the spin mixing. The SOC-induced spin mixing leads to spin flips as polarons hop from one molecule to another, giving rise to spin relaxation and diffusion. The SOC strengths in common organics are quantified based on first-principles calculations and their values in Alq₃ and in 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 Alq₃ from muon spin rotation and in CuPc from spin-polarized two-photon photoemission.

Biography

Zhi-Gang Yu，Senior Research Scientist，SRI International（斯坦福国际研究院）, USA

EDUCATION
1991-1996 Fudan University, China, PhD in Theoretical Condensed Matter Physics
1986-1991 University of Science and Technology of China (USTC), BS in Theoretical Physics

QUALIFICATION HIGHLIGHTS
Deep understanding of and broad experience in condensed matter physics, quantum statistical physics, and materials physics
Effective in establishing research directions, winning government funding, and leading multiple projects
Experienced in modeling of a variety of complex materials, including semiconductors, conducting polymers, transition-metal oxides, and biological systems for understanding and predicting their unusual electronic, optical, and transport properties, as well as novel electronic, spintronic, and optoelectronic device structures based on them
Self-motivated team player; skilled in communicating with scientists with different expertise
Able to formulate innovative solutions to challenges in complex systems; strong capabilities in analytical methods, algorithm development, and programming  
Excellent written and verbal communication skills

References

[1] Z. G. Yu, Spin-orbit coupling and its effects in organic solids, Phys. Rev. B 85, 115201 (2012) (Editors’ Suggestion)

[2] Z. G. Yu. Spin-orbit coupling, spin relaxation, and spin diffusion in organic solids,

Phys. Rev. Lett. 106, 106602 (2011).