Optical thermometry of anisotropic semimetal of WTe₂ using polarization-sensitive microscopy

We report an optical thermometry technique using a polarization-sensitive laser scanning microscopy. WTe₂ multilayer is heated by Joule heating from an alternating charge current, and its local temperature is detected via polarization rotation of the reflected light. We found a linear relationship between the temperature and the polarization rotation angle with a conversion coefficient of 25 ± 4 µrad/K. Considering the uncertain level of the polarization rotation microscopy, our system has a temperature resolution of less than 10 mK. We also confirmed that the spatial mapping of the temperature rise well matches the simulated current density distribution, which confirms that local heating is driven by Joule heating.