Abstract
The nonsymmetrized current noise is crucial for the analysis of light emission in nanojunctions. The latter represent non-classical photon emitters whose description requires a full quantum approach. It was found experimentally that light emission can occur with a photon energy exceeding the applied dc voltage, which intuitively should be forbidden due to the Pauli principle. This overbias light emission cannot be described by the single-electron physics, but can be explained by two-electron or even three-electron processes, correlated by a local resonant mode in analogy to the well-known dynamical Coulomb blockade (DCB). Here, we obtain the nonsymmetrized noise for junctions driven by an arbitrarily shaped periodic voltage. We find that when the junction is driven, the overbias light emission exhibits intriguingly different features compared to the dc case. In addition to kinks at multiples of the bias voltage, side kinks appear at integer multiples of the ac driving frequency. Our work generalizes the DCB theory of light emission to driven tunnel junctions and opens the avenue for engineered quantum light sources, which can be tuned purely by applied voltages.
Highlights
The study of the nature of shot noise [1] has progressed tremendously since its first prediction by Schottky [2] in 1918
We have shown that ac noises possess distinctly different features compared to the dc-case
We have generalized the excess quantum noise to the finite-frequency case and found the minima in the excess noise are shifted to N ≡ eV0/ωac = n + Ω/ωac and extra kinks arise at N = n − Ω/ωac
Summary
The study of the nature of shot noise [1] has progressed tremendously since its first prediction by Schottky [2] in 1918. Experiments in metallic tunnel contacts formed by a scanning tunneling microscope (STM) show that an unexpected light emission with energies larger than the bias can be observed [41, 42] This observation was subsequently termed overbias emission and cannot be explained by a single electron process involving one photon according to the standard DCB theory [33, 34] which takes only the Gaussian fluctuations into consideration. There is, still a lack of the general formula for the quantum noise of a contact driven by an arbitrarily shaped voltage, even without considering the light emission. This theory comprises the interaction with a local plasmon-polariton mode.
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