Thermoelectric Measurements on InAs/GaSb double Quantum Well

We performed thermoelectric measurement on InAs/GaSb double quantum well, in an attempt to observe thermal power and Nernst effect contributed by the helical edge channels. A new ``Semi-AC'' method was developed to conduct thermoelectric measurements for Hall bars with a size of $\sim$20 $\mu$m, which is more reliable in terms of determining charge carrier type compared with the 2-$\omega$ method. Furthermore, we will discuss thermoelectric signals under perpendicular magnetic field, in particular under Landau level quantization.