tunnel effecteffect

In 1928, George Gamow, Ronald Gurney and Edward Condon independently explained alpha decay: a particle inside the nucleus does not have enough energy to escape according to classical laws, but thanks to the wave properties of matter, there is a small probability of finding it outside — as if it passed through a wall without breaking it. Later, the effect found application in electronics: in 1957, Leo Esaki created the tunnel diode, where current flows through the forbidden zone of a semiconductor.

In the quantum world, a particle does not bounce off an obstacle like a ball off a concrete slab but can pass through. The probability of such passage is higher the thinner the barrier and the smaller the difference between the particle's energy and the barrier height. The effect arises from the wave nature of matter (particles behave as waves), which allows 'penetration' into forbidden regions.

The tunnel effect is a quantum mechanical phenomenon of a particle passing through a potential barrier whose energy exceeds the particle's kinetic energy. In classical physics, such a particle would reflect, but in quantum mechanics, the wave function exponentially decays inside the barrier and can have a non-zero amplitude beyond it. The transmission coefficient T for a rectangular barrier is approximately expressed by the formula: \( T \approx \exp\left(-\frac{2d}{\hbar}\sqrt{2m(V_0 - E)}\right) \), where \( d \) is the barrier width, \( m \) is the particle mass, \( V_0 \) is the height of the potential barrier, \( E \) is the particle energy, \( \hbar \) is the reduced Planck constant. The effect underlies many micro- and nanoelectronic devices, as well as nuclear processes.