Optical Spectroscopy of URu2Si2 A Search for New Features

Abstract

<p>In the past, optical measurements of single crystals have provided insights into phase transitions, the structure and symmetry of the superconducting gap and many other phenomena. Competing groups are perpetually trying to improve the accuracy of measurements to contribute to the understanding of the materials they study. Recent improvements at McMaster included the installation of a translating stage that allowed for submillimeter control of sample position, the measurement of several samples in one experiment, and measurements at temperatures of 10 - 300 K. The stage was attached to an external sample chamber on a spectrometer that can be used to measure frequencies from 20 to 38,000 cm^-1. The new sample stage was used in measurements of the reflectance spectra of a single crystal URu2Si2 sample. The reflectance measurements were used to calculate the absolute reflectance and optical conductivity.<br /><br />It was observed that for temperatures below 50 K at frequencies below 100 cm^-1 , the reflectance appeared to have a parabolic trend. A linear regression was used to fit the absolute reflectance measured by Dr. Angel (2010) in order to determine the numeric values of the parabolic model with the best fit data. The regression gave the optimized equation: P = 0.9872 - 8.0279E-6*ω² with a regression coefficient of 0.8417. This showed that over 84% of the variability in the data was accounted for by the model. This model was used to calculate the absolute reflectance from the thermal reflectance data at 3 K collected by Dr. Angel (2010) and was shown to have a standard deviation of ±0.011. The result was called the "refined" absolute reflectance, and the refining method was repeated on the thermal reflectance measurements conducted by Dr. Nagel's group.</p>