DMR-0507866: Carrier and Spin Dynamics in InSb- and InMnSbBased Heterostructures, PI: Giti Khodaparast, Physics Department, Virginia Tech.

The goal of this project is to study unexplored optical properties of InSb-based quantum wells with different confinement potentials and the newest member of III-V ferromagnetic structures, InMnSb, with an emphasis on dynamical aspects, including charge and spin dynamics. The samples are provided by groups of Prof. Furdyna,, University of Notre Dame and Prof. Santos,, University of Oklahoma. In analogy with the early development of semiconductor electronics, there is now a rapidly growing interest in the science and engineering of low-dimensional magnetic and narrow gap semiconductors. These structures have the potential to lead to revolutionary devices such as spin transistors, infrared spin-photonics, and novel switches for the next generation of computing. We use time resolved spectroscopy techniques such as pump/probe and magneto-optical Kerr effect (MOKE) to: (1) understand charge/spin dynamics in narrow gap structures with novel confinement potentials, (2) study phenomena such as interband and intraband photo-galvanic effects, in order to generate spin polarized current, (3) probe the effect of magnetic impurities on the spin/charge dynamics, and (4) develop concepts for spin based device applications.

In a time resolved optical pump/probe measurement, changes in the reflectivity or transmission as a function of the time delay between the pump and the probe can probe carrier dynamic.

Kerr/Faraday rotation corresponds to the rotation of the polarization plane of the reflected/transmitted light from the surface of a ferromagnet. The MOKE signal arises from the difference between the optical coefficients of a material for left and right circularly polarized light. This difference can be induced by an external magnetic field, an optically, or a spontaneous induced magnetization. We use optically induced magnetization to probe spin dynamic.

Photo-induced MOKE of InMnSb at 77K versus time delay under pumping with circularly polarized radiation at 850 nm and probing with the same wavelength. This is a measure of spin relaxation.Khodaparast et. al, Institute of Physics ConferenceProceeding 187, 517 (2006).

Group of Prof. Khodaparast at Physics Department,Virginia Tech.

Prof. Khodaparast supervises two undergraduate students; Brett Spencer and Emily wade, and three graduate students, Matt Frazier, Kanokwan Nontapot and Aliya gifford.

Brett Spencer, a senior, is assembling a closed cycled

cryostat to perform transport measurements on

semiconductor structures. He plans to go to graduate school

next year.

Emily wade is cooling down a ferromagnetic semiconductor sample

using liquid nitrogen to perform optical measurement with the help of a

graduate student, Kanokwan Nontapot.Emily is a junior and plans to go to

graduate school.

Sponsored by NSF DMR-0507866Undergraduate summer research was supported by NSF-REU supplement.