Abstract
Axion dark matter inevitably generates electromagnetic radiation in quantum Hall effect experiments that use strong magnetic fields. Although these emissions are very weak, we have shown using a QCD axion model that they influence the plateau-plateau transition at low temperatures (below 100 mK) in a system with a large surface area (greater than 10⁻³ cm²) of two-dimensional electrons. By analyzing previous experiments that show saturation of the transition width Δ B as temperature and microwave frequency change, we provide evidence for the presence of axions. Notably, in most experiments without axion effects, the saturation frequency f_s(T) is less than 1 GHz at temperatures of 100 mK or higher and for system sizes of 10⁻³ cm² or smaller. Additionally, the frequency f_s(T) decreases with decreasing temperature or increasing system size. However, there are experiments that show a saturation frequency f_s(T)≃ 2.4GHz despite a low temperature of 35 mK and a large surface area of 6.6× 10⁻³ cm² for the Hall bar. This identical frequency of approximately 2.4 GHz has also been observed in different plateau transitions and in Hall bars of varying sizes. These unexpected results are caused by axion microwaves. The saturation frequency f_s=m_a/2π of ≃ 2.4 GHz implies an axion mass of ≃ 10⁻⁵eV. By comparing the axion effect with thermal effect on the width Δ B, we have shown the dominance of the axion effect over thermal effect at low temperature less than 50mK. The dominance of the axion effect is attributed to significant absorption of axion energy, which is proportional to the square of the number of electrons involved.