Who proposed that all particles have an associated matter wave?

Louis de Broglie proposed that all particles have an associated matter wave.

In the early 1920s, de Broglie extended wave-particle duality beyond light. His 1924 doctoral thesis argued that matter particles, including electrons, should possess wave-like properties. He associated a particle of momentum p with a wavelength λ = h/p, now called the de Broglie wavelength. A particle’s wavelength therefore becomes shorter as its momentum increases.

De Broglie’s idea grew partly from the developing concept that light could behave both as a wave and as a collection of particles. He suggested that the same duality should apply to matter: particles can be detected as localized objects but can also diffract and interfere under suitable conditions. This proposal provided a foundation for Erwin Schrödinger’s wave mechanics.

The hypothesis was experimentally supported in 1927, when Clinton Davisson and George Paget Thomson independently observed electron diffraction. De Broglie received the 1929 Nobel Prize in Physics for his discovery of the wave nature of electrons. Macroscopic objects technically have matter wavelengths too, but those wavelengths are ordinarily far too small to observe easily.