Who proposed the matter-wave hypothesis in 1924?

Louis de Broglie proposed the matter-wave hypothesis in 1924.

De Broglie suggested that particles such as electrons should have wave properties, just as light can display both wave and particle behavior. He associated a wavelength with a particle’s momentum using the relation lambda = h divided by momentum.

The proposal extended wave–particle duality beyond electromagnetic radiation. It was initially a theoretical idea, but electron diffraction experiments soon provided direct evidence. In 1927, Clinton Davisson and Lester Germer observed electrons scattering from a nickel crystal, while George Paget Thomson observed electron diffraction independently.

De Broglie’s hypothesis became a foundation of wave mechanics and helped inspire Erwin Schrödinger’s wave equation. He received the 1929 Nobel Prize in Physics for the discovery of the wave nature of electrons. Matter waves are most noticeable for tiny particles; the wavelength of an everyday object is ordinarily far too small to observe.