CAREER: Time-Dependent Density-Functional Approach for Ultrafast Nonlinear Excitations in Semiconductors

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TECHNICAL EXPLANATION:This CAREER award supports theoretical research on ultrafast nonequilibrium carrier dynamics in photoexcited bulk semiconductors and semiconductor heterostructures. The education component focuses on developing an innovative course for teaching condensed matter physics to undergraduate students. The PI plans to reformulate the semiconductor Bloch equations within time-dependent density functional theory to study nonequilibrium carrier dynamics in photoexcited bulk semiconductors and semiconductor heterostructures on femtosecond to picosecond time scales. Time dependent density functional theory offers a computationally tractable formalism for describing dynamical correlation effects. The PI aims to evolve a more realistic theoretical picture by developing a formal framework that includes non-parabolic bands beyond the effective mass approximation, a treatment of exchange and correlation accounting for memory and retardation effects, and a microscopic description of disorder scattering of "hot" electron distributions. The PI will investigate whether a spatially long-ranged exchange-correlation potential together with the reformulated semiconductor Block equations can capture ultrafast excitonic dynamics. Previous work using long ranged exchange-correlation potentials did not enter the nonlinear ultrafast regime to be explored by this work. The PI ultimately aims to apply this formal framework to the coherent control of nonlinear intersubband effects such as optical bistability, harmonic generation, terahertz pulse shaping, and populating selected excited subbands.In the education component, the PI will focus on education in condensed matter physics. The PI plans to develop an upper undergraduate level condensed matter physics course including: (1) a course content that emphasizes topics at the forefront of modern science and technology, (2) interactive hands-on computer simulations, (3) student group projects that involve developing simulation programs. A public web site will also be created to make newly developed simulation routines available under the GNU General Public License. NON-TECHNICAL EXPLANATION:This CAREER award supports theoretical research on quantum mechanical states of electrons in semiconductors that result from illumination by light. Recent advances in laser technology have opened a frontier where the quantum mechanical states of electrons are prepared and probed by very short pulses of laser light. The PI will develop a theoretical technique to describe how electrons in semiconductors respond to very short pulses of laser light. The technique holds promise for a description that at once includes important materials specific information and is accessible to current computer technology. The PI plans to apply the technique to investigate the detailed dynamics of the electrons and how to prepare and control quantum mechanical states. This work is fundamental research and also contributes to the intellectual foundations of future technologies. In the education component, the PI will focus on education in condensed matter physics. The PI plans to develop an upper undergraduate level condensed matter physics course including: (1) a course content that emphasizes topics at the forefront of modern science and technology, (2) interactive hands-on computer simulations, (3) student group projects that involve developing simulation programs. A public web site will also be created to make newly developed simulation routines available under the GNU General Public License.