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CM/AMO SEMINAR<br> Symmetries and Spins in 2D Membranes and Traditional Semiconductors

Tuesday, April 23, 2013
12:00 AM
335 West Hall

Group theory is a powerful tool to investigate spin-dependent
transport and optical properties. It allows one to identify important
processes and to define the physics with a minimal set of material
dependent parameters. In this talk, I will present our recent findings
for two material classes.

Monolayer Transition-Metal Dichalogonides [1]: I will first delineate
the transport limitations via zeroth-order selection rules and make
connection with the energy relaxation of electrons, holes and hot
excitons. Then, I will expand on spin flips induced by flexural
phonons and show that the spin relaxation is ultrafast for electrons
in free-standing membranes while being mitigated in supported
membranes. This behavior is universal in 2D membranes that respect
mirror symmetry and it leads to a counterintuitive inverse relation
between mobility and spin relaxation. The findings will be compared
with the case of graphene.

Group IV semiconductors [2-6]: These materials are ideal choices for
spintronic devices due to their relatively long spin lifetimes and
mature technology. I will present our findings on the effects of
electron-phonon interaction on spin-dependent optical and transport
properties in Si and Ge.

[1] Y. Song and H. Dery, “Transport Theory of Monolayer
Transition-Metal Dichalcogenides”, preprint: arXiv 1302.3627 (2013).
[2] P. Li, D. Trivedi and H. Dery, “Spin-dependent optical properties
in strained silicon and germanium”, Phys. Rev. B 87, 115203 (2013).
[3] P. Li, Y. Song and H. Dery, “Intrinsic spin lifetime of conduction
electrons in germanium”, Phys. Rev. B 86, 085202 (2012).
[4] J. Li, L. Qing, H. Dery, and I. Appelbaum, “Field-induced negative
differential spin lifetime in silicon”, Phys. Rev. Lett. 108, 157201
[5] P. Li and H. Dery, “Spin-Orbit Symmetries of Conduction Electrons
in Silicon”, Phys. Rev. Lett. 107, 107203 (2011).
[6] P. Li and H. Dery, “Theory of spin-dependent phonon-assisted
optical transitions in silicon”, Phys. Rev. Lett. 105, 037204 (2010).