A New Look At Magnetic Semiconductors John Cerne, SUNY at Buffalo, DMR 0449899

The strong connection between their electrical and magnetic properties makes magnetic semiconductors such as GaMnAs highly exciting and rewarding, both in terms of providing new insight into fundamental concepts in physics well as technological applications, such as spintronics, quantum computing, and integrating non-volatile memory and processing into a single material system. Although the infrared wavelength range (ten to twenty times the wavelength of visible light) is critical to understanding these materials, exploration of the magneto-optical properties of these materials in this range has been limited. By studying how magnetic fields change the polarization (the shape of the light’s electric field wave) of infrared light as it passes through or reflects off these materials, this project provides valuable new information and has helped to address a major controversy. Measurements that look at the intensity, but not the polarization, of transmitted light in the infrared and measurements that look at the polarization at shorter wavelengths have suggested that the charge carriers that are responsible for the electrical and magnetic properties of GaMnAs hop from impurity to impurity. Our measurements, which probe these carriers more directly, show that they can be modeled accurately assuming that they move relatively freely, as charge carriers do in a metal. These results have been accepted for publication in Physical Review Letters in August 2009.

The rotation (top) and the ellipticity (bottom) of light that passes through several GaMnAs samples as a function of the energy of the light. From Acbas et al., Phys. Rev. Lett. (2009).

Conceptual Approach To Waves John Cerne, SUNY at Buffalo, DMR 0449899

We have created a web site that explains many basic wave concepts using dynamic and interactive graphical simulations. Here is an example of a graphical and more intuitive approach explaining why and how Fourier analysis allows us to find the frequency components that make up a wave. Fourier analysis is critical to many fields in science and technology, ranging from communications, acoustics, and even quantum mechanics. The simulation on the left allows the student to extract graphically individual frequency components (middle) in a function (top). Not only does this help teach basic concepts about Fourier analysis, it provides a graphical visualization of the mathematical treatment. Many new students find the equations associated with Fourier analysis intimidating and puzzling; here we allow students to see how the math works using interactive graphs.

Interactive Fourier analysis demonstration from:http://electron.physics.buffalo.edu/claw. Top plot shows a signal containing several frequency components, middle trace contains a single reference frequency signal, and the bottom trace shows the product of these two functions. The average of this product is displayed on the right for different reference frequencies. The student tries different reference frequencies to find the components that are contained in the top plot.