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Register a new userNon-classical current noise and light emission of an ac-driven tunnel junction
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The non-symmetrized 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 non-symmetrized 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.
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The transport properties of a simple model for a finite level structure (a molecule or a dot) connected to metal electrodes in an alternating current scanning tunneling microscope (AC-STM) configuration is studied. The finite level structure is assumed to have strong binding properties with the metallic substrate, and the bias between the STM tip and the hybrid metal-molecule interface has both an AC and a DC component. The finite frequency current response and the zero frequency photo-assisted shot noise are computed using the Keldysh technique, and examples for a single site molecule (a quantum dot) and for a two-site molecule are examined. The model may be useful for the interpretation of recent experiments using an AC-STM for the study of both conducting and insulating surfaces, where the third harmonic component of the current is measured. The zero frequency photo-assisted shot noise serves as a useful diagnosis for analyzing the energy level structure of the molecule. The present work motivates the need for further analysis of current fluctuations in electronic molecular transport.
We report the first measurement of the emph{dynamical response} of shot noise (measured at frequency $omega$) of a tunnel junction to an ac excitation at frequency $omega_0$. The experiment is performed in the quantum regime, $hbaromegasimhbaromega_0gg k_BT$ at very low temperature T=35mK and high frequency $omega_0/2pi=6.2$ GHz. We observe that the noise responds in phase with the excitation, but not adiabatically. The results are in very good agreement with a prediction based on a new current-current correlator.
We theoretically investigate the critical current of a thermally-biased SIS Josephson junction formed by electrodes made by different BCS superconductors. The response of the device is analyzed as a function of the asymmetry parameter, $r=T_{c_1} /T_{c_2}$. We highlight the appearance of jumps in the critical current of an asymmetric junction, namely, when $r eq1$. In fact, in such case at temperatures at which the BCS superconducting gaps coincide, the critical current suddenly increases or decreases. In particular, we thoroughly discuss the counterintuitively behaviour of the critical current, which increases by enhancing the temperature of one lead, instead of monotonically reducing. In this case, we found that the largest jump of the critical current is obtained for moderate asymmetries, $rsimeq3$. In view of these results, the discussed behavior can be speculatively proposed as a temperature-based threshold single-photon detector with photon-counting capabilities, which operates non-linearly in the non-dissipative channel.
We report the first experimental data of the third moment of current fluctuations in a tunnel junction. We show that both in the classical and quantum regimes (low or high frequency as compared to voltage), it is given by $S_{I^3}=e^2I$. We discuss environmental effects in both regimes.
We propose a conceptually new way to gather information on the electron bands of buried metal(semiconductor)/insulator interfaces. The bias dependence of low frequency noise in Fe$_{1-x}$V$_{x}$/MgO/Fe (0 $<$ x $<$ 0.25) tunnel junctions show clear anomalies at specific applied voltages, reflecting electron tunneling to the band edges of the magnetic electrodes. The change in magnitude of these noise anomalies with the magnetic state allows evaluating the degree of spin mixing between the spin polarized bands at the ferromagnet/insulator interface. Our results are in qualitative agreement with numerical calculations.
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