Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review Letters

Coherent Multiple Charge Transfer in a Superconducting NbN Tunnel Junction

Yoshinori Uzawa, Z. Wang

Published Jun 29, 2005• 22 citations
Publisher

Abstract

We measured shot noise and submillimeter-wave response in a superconducting NbN tunnel junction that had a subharmonic gap structure on the current-voltage (I-V) curve. We found that the observed effective charge, defined from the noise-current ratio, tends to a steplike function of voltage. In the presence of submillimeter-wave radiation of frequency v, novel step structures spaced by hv/2e below and above the half-gap voltage clearly appeared on the I-V curve, overlapping the ordinary photon-assisted tunneling steps spaced by hv/e. Observation of these features provides clear evidence that coherent multiple Andreev reflection processes occur in the NbN tunnel junction with low barrier transparency.

DOI
10.1103/physrevlett.95.017002

Related papers

Subharmonic Photon-Assisted Tunneling Effect in Superconducting NbN Tunnel Junctions

Yoshinori Uzawa, Mahoto Takeda, Akira Kawakami +1 more

We investigated subharmonic gap structures in the current-voltage (I-V) characteristics of NbN tunnel junctions by observing frequency response using a quasioptical mixer configuration. We chose a 10.5-/spl mu/m-long by 0.6-/spl mu/m-wide junction for the mixer so that the junction behaved as a distributed element at submillimeter-wave frequencies in wideband observations. In the presence of electromagnetic waves, subharmonic photon-assisted tunneling steps with a voltage width of hf/2e could clearly be observed below and above the half-gap voltage in the I-V curves of junctions at measured frequencies from 600 to 950 GHz, where h is Planck's constant, f is frequency, and e is electron charge. This evidence is consistent with a consequence of multiple Andreev reflection at low transmissions or multiparticle tunneling.

IEEE Transactions on Applied Superconductivity•Jun 1, 2005•1 citation

Shot Noise in NbN/AlN/NbN Superconducting Tunneling Junctions

Dong Liu, Jie Hu, Ming Yao +2 more

With sensitivity approaching the quantum limit, superconductor-insulator-superconductor (SIS) mixers play an important role in radio astronomy and atmospheric science at millimeter and submillimeter wavelengths. As one of the intrinsic noise sources in superconducting tunneling junctions, shot noise is still not well understood, particularly for those of relatively high energy gap (e.g., NbN/AlN/NbN). In this paper, we mainly study the multiple Andreev reflection (MAR) enhanced shot noise of two different NbN SIS junctions (i.e., junction array and long junction) as well as their temperature dependence. Barrier strength Z is taken into consideration for theoretical analysis of effective charge of the MAR effect based on the Blonder-Tinkham-Klapwijk (BTK) theory with the Andreev clusters method. It has been found that the effective charge of the MAR effect is inversely proportional to temperature, the barrier strength Z and transparency T are proportional to temperature. Detailed measurement results and analysis will be presented.

IEEE Transactions on Applied Superconductivity•Nov 7, 2016•1 citation

Shot Noise and Coherent Multiple Charge Transfer in Superconducting Quantum Point Contacts

Juan Carlos Cuevas, A. Martín‐Rodero, A. Levy Yeyati

We analyze the shot noise in a voltage biased superconducting quantum point contact. Results are presented for the single channel case with arbitrary transmission. In the limit of very low transmission it is found that the effective charge, defined from the noise-current ratio, exhibits a steplike behavior as a function of voltage with well-defined plateaus at integer values of the electronic charge. This multiple charge corresponds to the transmitted charge in a multiple Andreev reflection (MAR) process. This effect gradually disappears for increasing transmission due to interference between different MAR processes.

arXiv:cond-mat/9812175•Physical Review Letters•May 17, 1999•102 citations

Submillimeter wave responses in NbN/AlN/NbN tunnel junctions

Yoshinori Uzawa, Zhen Wang, Akira Kawakami +1 more

The submillimeter wave frequency responses of NbN/AlN/NbN tunnel junctions have been investigated using quasioptical coupling techniques and an optically pumped far-infrared laser. A two junction array was integrated at the feeds of a bowtie antenna. Measurements on the junctions were made by monitoring photon-assisted tunneling steps induced in the current–voltage characteristics. These n=±1 photon steps were clearly observed with irradiation at 303, 594, 693, and 762 GHz. The results suggest it will be possible to realize submillimeter wave mixers by using these junctions.

Applied Physics Letters•Apr 10, 1995•19 citations

Shot noise in NbN SIS junctions suitable for THz radiation detection

Pieter Dieleman, Herman van de Stadt, T. M. Klapwijk +2 more

We study the behavior of NbN SIS junctions as radiation detectors with emphasis on the shot noise generated at voltages below the gap voltage. The intrinsically large subgap current of NbN junctions is carried by pinholes with a conduction attributed to multiple Andreev reflection, leading to transported charges q much greater than e. Using this charge enhancement mechanism we explain the junction shot noise characteristics in the unpumped case as well as in the pumped case. The measured mixer noise temperature in the pumped case is more than twice that calculated with standard Tucker theory. The measured double side band noise temperatures are 1450 K at 600 GHz and 2800 K at 950 GHz.

•Jan 1, 1997•1 citation

Nonlinear response of tunnel-type Josephson junctions at submillimeter-wave frequencies

S. Morita, S. Takaki, S. Imai +2 more

We have fabricated tunnel-type Josephson junctions with very small junction area by pressing the tip of a sharpened Nb wire onto a thinly oxidized Sn film, and studied their submillimeter-wave responses. It turns out that the junctions have a very high cutoff frequency, and are suitable for the investigation of the response to the submillimeter waves with the frequency higher than 1 THz. From the frequency and laser-power dependence of the Shapiro step, it is found that the tunnel-type junction shows much larger higher-order steps, and accordingly has much stronger nonlinearity than the bridge-type junction in the submillimeter-wave region. The large enhancement of the steps due to the Riedel singularity is also observed in the tunnel-type junction. In addition to the Shapiro steps, photon-assisted tunneling steps are observed clearly, reflecting the large and sharp gap structure in the dc IV curves of the tunnel-type junctions.

IEEE Transactions on Magnetics•May 1, 1983•6 citations
We measured shot noise and submillimeter-wave response in a superconducting NbN tunnel junction that had a subharmonic gap structure on the current-voltage (I-V) curve. We found that the observed effective charge, defined from the noise-current ratio, tends to a steplike function of voltage. In the presence of submillimeter-wave radiation of frequency v, novel step structures spaced by hv/2e below and above the half-gap voltage clearly appeared on the I-V curve, overlapping the ordinary photon-assisted tunneling steps spaced by hv/e. Observation of these features provides clear evidence that coherent multiple Andreev reflection processes occur in the NbN tunnel junction with low barrier transparency.
We investigated subharmonic gap structures in the current-voltage (I-V) characteristics of NbN tunnel junctions by observing frequency response using a quasioptical mixer configuration. We chose a 10.5-/spl mu/m-long by 0.6-/spl mu/m-wide junction for the mixer so that the junction behaved as a distributed element at submillimeter-wave frequencies in wideband observations. In the presence of electromagnetic waves, subharmonic photon-assisted tunneling steps with a voltage width of hf/2e could clearly be observed below and above the half-gap voltage in the I-V curves of junctions at measured frequencies from 600 to 950 GHz, where h is Planck's constant, f is frequency, and e is electron charge. This evidence is consistent with a consequence of multiple Andreev reflection at low transmissions or multiparticle tunneling.
With sensitivity approaching the quantum limit, superconductor-insulator-superconductor (SIS) mixers play an important role in radio astronomy and atmospheric science at millimeter and submillimeter wavelengths. As one of the intrinsic noise sources in superconducting tunneling junctions, shot noise is still not well understood, particularly for those of relatively high energy gap (e.g., NbN/AlN/NbN). In this paper, we mainly study the multiple Andreev reflection (MAR) enhanced shot noise of two different NbN SIS junctions (i.e., junction array and long junction) as well as their temperature dependence. Barrier strength Z is taken into consideration for theoretical analysis of effective charge of the MAR effect based on the Blonder-Tinkham-Klapwijk (BTK) theory with the Andreev clusters method. It has been found that the effective charge of the MAR effect is inversely proportional to temperature, the barrier strength Z and transparency T are proportional to temperature. Detailed measurement results and analysis will be presented.
We analyze the shot noise in a voltage biased superconducting quantum point contact. Results are presented for the single channel case with arbitrary transmission. In the limit of very low transmission it is found that the effective charge, defined from the noise-current ratio, exhibits a steplike behavior as a function of voltage with well-defined plateaus at integer values of the electronic charge. This multiple charge corresponds to the transmitted charge in a multiple Andreev reflection (MAR) process. This effect gradually disappears for increasing transmission due to interference between different MAR processes.
The submillimeter wave frequency responses of NbN/AlN/NbN tunnel junctions have been investigated using quasioptical coupling techniques and an optically pumped far-infrared laser. A two junction array was integrated at the feeds of a bowtie antenna. Measurements on the junctions were made by monitoring photon-assisted tunneling steps induced in the current–voltage characteristics. These n=±1 photon steps were clearly observed with irradiation at 303, 594, 693, and 762 GHz. The results suggest it will be possible to realize submillimeter wave mixers by using these junctions.
We study the behavior of NbN SIS junctions as radiation detectors with emphasis on the shot noise generated at voltages below the gap voltage. The intrinsically large subgap current of NbN junctions is carried by pinholes with a conduction attributed to multiple Andreev reflection, leading to transported charges q much greater than e. Using this charge enhancement mechanism we explain the junction shot noise characteristics in the unpumped case as well as in the pumped case. The measured mixer noise temperature in the pumped case is more than twice that calculated with standard Tucker theory. The measured double side band noise temperatures are 1450 K at 600 GHz and 2800 K at 950 GHz.
We have fabricated tunnel-type Josephson junctions with very small junction area by pressing the tip of a sharpened Nb wire onto a thinly oxidized Sn film, and studied their submillimeter-wave responses. It turns out that the junctions have a very high cutoff frequency, and are suitable for the investigation of the response to the submillimeter waves with the frequency higher than 1 THz. From the frequency and laser-power dependence of the Shapiro step, it is found that the tunnel-type junction shows much larger higher-order steps, and accordingly has much stronger nonlinearity than the bridge-type junction in the submillimeter-wave region. The large enhancement of the steps due to the Riedel singularity is also observed in the tunnel-type junction. In addition to the Shapiro steps, photon-assisted tunneling steps are observed clearly, reflecting the large and sharp gap structure in the dc IV curves of the tunnel-type junctions.