Optical detection of charge accumulation in an electrically anisotropic semimetal of WTe₂

Charge accumulation in a current-injected device provides important information about the electrical properties of materials. Conventionally, local charge accumulation is measured by potential drops at multiple positions in the device using a voltage probe. Here, we report on direct observations of the spatial distribution of charge accumulation in semimetal WTe₂ via the polarization rotation microscopy technique. The mappings of the polarization rotation of the reflected light show that the injected charge carriers accumulate near the transverse boundaries of the device. Our results demonstrate an optical method to visualize charge accumulation profiles of the electrically anisotropic medium.