Eddie Worrell

Major: Engineering Physics 

Mentors: Juan Gaitan, Mark Sherwin

Probing THZ Driven Excitons in Magnetic and Conventional Semiconductors

When a terahertz field is driven into a material, it is theorized that excitons in conventional semiconductors, such as gallium arsenide, will first ionize and then stabilize with increasing field strength. This adiabatic stabilization is something we aim to observe using absorption spectroscopy techniques. We first predict to see the exciton peak broaden and suppress asymmetrically as a result of the Thz coupling to and disrupting the exciton. Then, the peak will again narrow, indicating an increase in exciton lifetime. The ionization rate can be extracted from fitting the fano resonance to the absorption line shapes. As a mott insulator, Nickel phosphorus trisulphide excitons pair in different ways than a conventional semiconductor. NiPS3 excitons rely on the antiferromagnetic ordering of the material to survive, and this ordering is only present below 150 K. These excitons are far more robust, with a 40 binding energy of a few hundred meV , and they do not arise out of conventional band theory. We hope to use Thz pump and photoluminescence or absorbance probe to observe magnon- exciton coupling in absorption data by observing how the exciton spectrum changes under resonant pumping of magnon mode at 300 Ghz, and phonon- exciton coupling in photoluminescence data. NiPS3 samples have been prepped using an exfoliation and stacking technique using tape and a polymer stamp, as this Van der Waals material can be stripped down to atomically thin layers. Control data has been taken on bulk and quantum well gallium arsenide using absorption spectroscopy with near infrared LED in the range of 820 - 870 nm.