In condensed matter physics, the diffuson is a disorder-averaged electron-hole propagator, a mathematical object which often appears in the theory of disordered electronic systems. The poles of the propagator can be identified with diffusion modes.^[1][2]

In a disordered system, the motion of an electron is not ballistic, but diffusive: i.e., the electron does not move along a straight line, but experiences a series of random scatterings off of impurities. This random motion (diffusion) is described by a differential equation, known as the diffusion equation. The diffuson is the Green's function of the diffusion equation.^[1]

The diffuson plays an important role in the theory of electron transport in disordered systems, especially for phase coherent effects such as universal conductance fluctuations.^[3]