The Discoery of Electron Waves
In 1924 Louis De Broglie developed a theory on electron waves which he had published in earlier scientific journals. De Broglie’s theories were confirmed via diffract experiments. In which electrons are pushed through a slit or slits and give a wave-like pattern and behave like a wave. Louis’s theory confirmed that particles have wave-like properties.
https://www.britannica.com/biography/Louis-de-Broglie
https://chem.libretexts.org/Courses/Pacific_Union_College/Quantum_Chemistry/01%3A_The_Dawn_of_the_Quantum_Theory/1.07%3A_de_Broglie_Waves_can_be_Experimentally_Observed