de  Broglie  waves : Louis de Broglie proposed that, since light waves have particle characteristics, material particles must also posses  wave  like  character. This  is known as the de Broglie hypothesis.   The  de  Broglie  wavelength associated  with  a particle which is moving with momentum p, is

l = h/p (de Broglie equation)

where h is the Planck's constant.

Obviously the wavelength of macroscopic particles will be so small  that  they cannot  be detected. For atomic and subatomic particles like electrons, neutrons etc. the de-Broglie wavelength can be observed through interference, diffraction of these waves.