What experiment demonstrates the wave-particle duality of electrons?

The experiment that demonstrates the wave-particle duality of electrons is the double-slit experiment.

When electrons pass through two closely spaced slits without which-slit detection, they produce an interference pattern on a screen. That pattern is characteristic of waves. Yet the screen records each electron as a single localized impact, revealing particle-like behavior. Even when electrons are fired one at a time, the interference pattern gradually builds up from many individual detections.

The experiment grew from Thomas Young’s 1801 double-slit work with light. Electron versions became historically important in 1927, when Clinton Davisson and Lester Germer, and independently George Paget Thomson with Alexander Reid, demonstrated electron diffraction. Modern double-slit arrangements make the wave behavior especially intuitive.

A common mistake is to treat the electron as switching between being a classical wave and a classical particle. Quantum mechanics instead describes it with a wavefunction whose probability amplitudes interfere. If the apparatus records which slit the electron takes, the interference pattern disappears because the path information destroys the relevant coherence. Davisson–Germer is also evidence for electron wave behavior, but it is a different experiment.