Nonequilibrium fluctuations in normal-metal point contacts

Electrical fluctuations are investigated in normal-metal point contacts of small diameter (d ≈ 102 Å). Without allowance for the electron-phonon interaction the contact has no shot noise and the fluctuations in this case are determined only by the thermal (Nyquist) noise. A kinetic equation with random forces on the right-hand side is used to calculate the fluctuations due to the finite electron-phonon relaxation length lph. The order of magnitude of the spectral intensity of the fluctuations is Sv(ω)∼eVR(d/lph)−1 Owing to the dependence of lph on V the fluctuations grow nonlinearly with increasing voltage. In this case at T = 0 the relation d2Sv(ω)/dV2 =const G(eV) is obtained, G(v)=α^2(v)F(v) being the point-contact function of the electron-phonon interaction constant of the metal. Thus, in the high-frequency range investigation of the point-contact noise spectrum can serve as a method of “noise spectroscopy” of the electron–phonon interaction in metals.

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