Optical Microscopy And Spectroscopy At Low Temperatures And High Magnetic Fields

Abstract

This dissertation examines my efforts to develop an optical platform to explore low temperature and high magnetic field materials and device characterization. I have developed a modular scanning confocal microscopy platform using room temperature light generation and analysis which relies on an optical fiber to couple light from ambient conditions into a low temperature and high magnetic field sample environment. I have built two microscopes: one for operation in a dilution refrigerator at temperatures below 100 mK and magnetic fields of <9 T, and one for operation in a liquid He bath cryostat with a 7 Tx1 Tx1 T vector magnet. Both of these microscopes allow for concurrent sample transport measurements. I apply these microscopes to the study of the electron nematic phase of Sr3 Ru2 O7 through polarization microscopy and to the study of the magnetoluminescence of bulk single crystal CdTe and single layer MoSe2 . I report optical polarization measurements of Sr3 Ru2 O7 while tuning through the electron nematic phase transitions reported below 1 K and at 8 T, with sample base temperatures as low as 120 mK. I demonstrate the breaking of valley degeneracy in single layer MoSe2 with applied magnetic fields through polarization resolved photoluminescence measurements with out-of-plane fields up to 6.7 T. I demonstrate that the emission from MoSe2 becomes circularly-polarized in magnetic field even with unpolarized excitation, and that the degree of this polarization can be increased to about 50% by gating the sample. This suggests that electric fields can facilitate the generation of valley-population imbalance in samples where valley degeneracy has been broken by magnetic field. Finally I present preliminary efforts to incorporate two dimensional transition metal dichalcogenides (TMDs) with ferroelectric thin films for ferroelectricly gated semiconductor devices.