Researcher(s)
- Alexander Hutchinson, Material Science, University of Delaware
Faculty Mentor(s)
- Chitraleema Chakraborty, Physics and Astronomy, Materials Science and Engineering, University of Delaware
Abstract
The optoelectronic properties of two-dimensional (2D) materials, specifically transition metal dichalcogenides (TMDs), make these materials promising candidates for quantum devices. Due to the strong spin-valley coupling and inversion symmetry breaking of monolayer TMDs, two distinct momentum valleys are formed, where the carriers in the different valleys are excited with left- or right-handed circularly polarized light (σ+ or σ-). The degree of polarization (DOP) between the separate circularly polarized states across a range of applied magnetic field strengths (-7T to +7T) can be measured via polarization-resolved photoluminescence measurements. These measurements are used to obtain the g-factor values associated with various excitonic and defect transitions. To take these measurements, a confocal microscope integrated with a cryostat capable of temperatures as low as 2K was constructed. However, because this is a new system, it is crucial to calibrate all optical components and troubleshoot any errors to ensure measurements are clear, accurate, and reproducible. Systematic calibration of both the excitation and collection arms of the microscope was undertaken, with a specific focus on aligning the linear polarizer and quarter-wave plates. Benchtop testing demonstrated a degree of circular polarization (DOCP) of >96% for both excitation polarization states. Key sources of depolarization were found to occur due to scattering from optics in the collection arm, such as glass plates, along with misalignment of polarizers. By addressing these errors, a DOCP of ~96% was achieved in the collection arm for both σ+ incoming light; however, σ– incoming light yielded a ~86% DOCP due to minor beam shifting during polarization switching. Calibration will be validated by measuring the defect and neutral exciton g-factor of a known TMD sample before beginning a series of studies focused on the effects of defects on spin-valley interactions in TMD materials such as tungsten diselenide (WSe2).