Ultrafast Nonlinear Physics in Graphene: Explore the Limit of Phase Space Filling at 10^(-14) Second

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Date/Time:Monday, 31 Jan 2011 from 4:10 pm to 5:10 pm
Location:Physics, Room 5
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Jigang Wang (Iowa State University)

Exploring ultrafast nonlinear photoexcitations of high-density quasiparticles in low-dimensional solids represents one of the most fundamental yet technologically important themes. Such nonlinearities can evolve in the highly non-equilibrium, non-thermal states at femtosecond timescales largely driven by dynamics and interactions of quasi-particles instead of thermal perturbations. These lead to saturable absorption, gain, loss modulation and lasing, the basis of modern laser technology, telecommunications and metrology. Recently, graphene has gradually emerged as a prominent nonlinear model system for ultrafast photonics and condensed matter physics by engaging, e.g., linear Dirac spectrum and electron-hole symmetry. In this talk, I will review some new ultrafast nonlinear spectroscopy capabilities being developed in my group at Iowa State, and present some results in graphene as an example for applying them in the exploration of ultrafast materials science. Soecifically, we reveal photoinduced femtosecond nonlinear saturation and complete transparency of extremely dense fermions in graphene monolayers, and determine the maximum density excited by a single laser pulse of 40 fs. Together with simulations, we show carrier-carrier scattering thermalizes highly non-equilibrium fermion distribution within 40 fs with negligible carrier-phonon scattering, revealing, particularly, a regime of femtosecond quantum physics established by the interplay of band filling and photoinduced transparency.

This work is done in collaboration with T. Li, L. Luo, J. Zhang, M. Hupalo, M. C. Tringides, and J. Schmalian

Brief Bibliography:
Dr. Wang got his B.S. degree in physics in Jilin University, China and then he went to Rice University for his M.S and Ph.D under Dr. Jun Kono. Following his graduation in 2005, he went to Lawrence Berkeley National Lab working with Dr. Daniel Chemla as posdoc. In 2008, He joined Iowa State University as an assistant professor in physics. His current research focuses on developing ultrafast spectroscopy techniques from ultraviolet to terahertz, and applying them to nanostructures such as graphene and carbon nanotubes, metamaterials and correlated electrons such as manganites and ferromagnetic semiconductors. Dr. Wang received NSF CAREER award in 2010.