The complex ac conductance G(ω₀) of a system measures the dynamical response of the current to a small voltage excitation at frequency ω₀. It cannot in general be deduced from the only knowledge of the dc I(V ) characteristics. Similarly, we investigate the dynamical response of current noise to an ac excitation, i.e. the in-phase and out-of-phase response of current noise density S(ω) measured at frequency ω. We present a detailed calculation of this new response function χ_ω0 (ω), that we name noise susceptibility, at arbitrary frequencies for a coherent conductor in the scattering matrix formalism. We exemplify the relevance of our calculation by the measurement of the noise susceptibility of a tunnel junction in the quantum regime &barh;ω ~ &barh;ω₀> >k_BT, which is in remarkable agreement with our theory.

Date Published: 8 June 2007
PDF: 12 pages
Proc. SPIE 6600, Noise and Fluctuations in Circuits, Devices, and Materials, 66000T (8 June 2007); doi: 10.1117/12.724656

Published in SPIE Proceedings Vol. 6600:
Noise and Fluctuations in Circuits, Devices, and Materials
Massimo Macucci; Lode K.J. Vandamme; Carmine Ciofi; Michael B. Weissman, Editor(s)