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

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Low-temperature scanning electron microscopy of niobium superconducting tunnel junctions with trapping blocks

P. H. Videler, N. Rando, P. Verhoeve, Anthony J. Peacock, S. Lemke, Jens Martin, R. Gross, Rudolf Peter Huebener, John M. Lumley

Published Sep 16, 1994• 5 citations
Publisher

Abstract

In this paper we investigate the QP transport and loss mechanisms in a superconducting tunnel junction using the Low Temperature Scanning Electron Microscopy (LTSEM) technique. This approach allows precise control of the energy and position of a deposited electron pulse, which, within certain conditions, simulates the X-ray photo-absorption process. An Nb-Al-AlOxNb junction designed as a test structure which included Al blocks in the leads to act as quasiparticle traps, has been investigated. Asymmetries in the LTSEM signal distribution can be qualitatively described from the device geometry. From both the spatial distribution can be qualitatively described from the device geometry. From both the spatial distribution and the time resolved measurements the diffusion length in the amorphous Nb was determined to be of the order of 8 micrometers . The LTSEM technique has demonstrated that quasiparticles produced in the leads cannot enter the tunnel barrier due to the presence of the Al traps.

DOI
10.1117/12.186833

Related papers

Low barrier ZrO x -based Josephson junctions

Jae‐Hong Choi, Maciej Olszewski, Luojia Zhang +8 more

The Josephson junction is a crucial element in superconducting devices, and niobium is a promising candidate for the superconducting material due to its large energy gap relative to aluminum. AlOx has long been regarded as the highest quality oxide tunnel barrier and is often used in niobium-based junctions. Here, we propose ZrOx as an alternative tunnel barrier material for Nb electrodes. We theoretically estimate that zirconium oxide has excellent oxygen retention properties and experimentally verify that there is no significant oxygen diffusion leading to NbOx formation in the adjacent Nb electrode. We develop a top–down, subtractive fabrication process for Nb/Zr–ZrOx/Nb Josephson junctions, which enables scalability and large-scale production of superconducting electronics. Using cross-sectional scanning transmission electron microscopy, we experimentally find that depending on the Zr thickness, ZrOx tunnel barriers can be fully crystalline with chemically abrupt interfaces with niobium. Further analysis using electron energy loss spectroscopy reveals that ZrOx corresponds to tetragonal ZrO2. Room temperature characterization of fabricated junctions using Simmons’ model shows that ZrO2 exhibits a low tunnel barrier height, which is promising in merged-element transmon applications. Low temperature transport measurements reveal sub-gap structure, while the low-voltage sub-gap resistance remains in the megaohm range.

arXiv:2508.11593•APL Materials•Nov 1, 2025•4 citations

Dynamics and energy distribution of nonequilibrium quasiparticles in superconducting tunnel junctions

K. Segall, Christopher M. Wilson, L. Li +4 more

We present a full theoretical and experimental study of the dynamics and energy distribution of nonequilibrium quasiparticles in superconducting tunnel junctions (STJ's). STJ's are often used for single-photon spectrometers, where the numbers of quasiparticles excited by a photon provide a measure of the photon energy. The magnitude and fluctuations of the signal current in STJ detectors are in large part determined by the quasiparticle dynamics and energy distribution during the detection process. We use this as motivation to study the transport and energy distribution of nonequilibrium quasiparticles excited by x-ray photons in a lateral, imaging junction configuration. We present a full numerical model for the tunneling current of the major physical processes which determine the signal. We find that a diffusion framework models the quasiparticle dynamics well and that excited quasiparticles do not equilibrate to the lattice temperature during the time scales for tunneling. We extract physical time scales from the measured data, make comparisons with existing theories, and comment on implications for superconducting mesoscopic systems and single-photon detectors.

arXiv:cond-mat/0402056•Physical Review B•Dec 16, 2004•24 citations

Spatially resolved studies of the microwave properties of superconducting devices

D. Quenter, S. Stehle, T. Doderer +8 more

Low temperature scanning electron microscopy (LTSEM) offers the possibility for spatially resolved investigations of microwave properties of single Josephson junctions, superconducting striplines, resonators, and complex cryoelectric circuits during their operation. The spatial resolution of about 1 μm is at least two orders of magnitude better than the typical wavelength (≳100 μm in the elements) in the frequency range of interest (50–500 GHz). We demonstrate that LTSEM is a well suited tool for the experimental investigation of superconducting microwave devices and cryoelectronic circuits.

Applied Physics Letters•Oct 11, 1993•11 citations

Dynamics of nonequilibrium quasiparticles in narrow-gap superconducting tunnel junctions

Alexander G. Kozorezov, R. A. Hijmering, Guy Brammertz +6 more

The latest generation of high quality, narrow gap, superconducting tunnel junctions (STJs) exhibits a steady-state and time-dependent behavior which cannot be described satisfactorily by previous treatments of nonequilibrium quasiparticle (qp) dynamics. These effects are particularly evident in experiments using STJs as detectors of photons, over the range from near infrared to x ray. In this paper, we present a detailed theoretical analysis of the spectral and temporal evolution of the nonequilibrium qp and phonon distributions in such STJs excited by single photons, over a wide range of excitation energy, bias voltage, and temperature. By solving the coupled set of kinetic equations describing the interacting excitations, we show that the nonequilibrium qp distribution created by the initial photoabsorption does not decay directly back to the initial undisturbed state in thermal equilibrium. Instead, it undergoes a rapid adiabatic relaxation to a long-lived, excited state, the spectral distribution of which is nonthermal, maintained by a balance between qp creation, recombination, and trapping. The model is able to describe successfully photoabsorption data taken on several different aluminum STJs, using a single set of parameters. Of particular note is the conclusion that the local traps responsible for qp loss are situated specifically in the region of Nb contacts.

Physical Review B•Jan 2, 2008•15 citations

Quantitative measurement of the microwave distribution in superconducting tunnel junctions

Richard A. Gerber, D. Quenter, T. Doderer +6 more

Low temperature scanning electron microscopy offers the possibility to measure the microwave distribution inside Josephson tunnel junctions in a quantitative way. The junctions are coupled to an external microwave source. Our results confirm the established model for the propagation of microwaves inside the junction stripline. Our method yields microwave specific parameters of the junction such as wavelength, microwave attenuation, reflection coefficients, and phase shifts.

Applied Physics Letters•Mar 20, 1995•6 citations

Scanning tunneling microscopy and spectroscopy characterization of Nb films for quantum applications

G. Berti, Carlos G. Torres‐Castanedo, Dominic P. Goronzy +5 more

Niobium thin films are key components of superconducting microwave resonators. Interest in these devices has increased dramatically because of their application in quantum systems. Despite tremendous effort to improve their performance, loss mechanisms are still not well understood. Nb/substrate and Nb/air interfaces are likely culprits in contributing to decoherence and ultimately limiting the performance of superconducting devices. Here, we investigate the Nb/substrate interface by studying the effect of hydrogen-passivated H:Si(111) substrates on the local superconducting properties of ∼40 nm thick Nb films compared to Nb films grown on typical Si(001) substrates. Specifically, low-temperature scanning tunneling microscopy and spectroscopy are employed to compare nanoscale material properties. The atomically flat monohydride H:Si(111) substrates are found to yield a smoother and less defective interface with the Nb film. Correspondingly, the Nb films grown on H:Si(111) substrates present more uniform superconducting properties and exhibit less quasiparticle broadening.

Applied Physics Letters•May 9, 2023•13 citations
In this paper we investigate the QP transport and loss mechanisms in a superconducting tunnel junction using the Low Temperature Scanning Electron Microscopy (LTSEM) technique. This approach allows precise control of the energy and position of a deposited electron pulse, which, within certain conditions, simulates the X-ray photo-absorption process. An Nb-Al-AlOxNb junction designed as a test structure which included Al blocks in the leads to act as quasiparticle traps, has been investigated. Asymmetries in the LTSEM signal distribution can be qualitatively described from the device geometry. From both the spatial distribution can be qualitatively described from the device geometry. From both the spatial distribution and the time resolved measurements the diffusion length in the amorphous Nb was determined to be of the order of 8 micrometers . The LTSEM technique has demonstrated that quasiparticles produced in the leads cannot enter the tunnel barrier due to the presence of the Al traps.
The Josephson junction is a crucial element in superconducting devices, and niobium is a promising candidate for the superconducting material due to its large energy gap relative to aluminum. AlOx has long been regarded as the highest quality oxide tunnel barrier and is often used in niobium-based junctions. Here, we propose ZrOx as an alternative tunnel barrier material for Nb electrodes. We theoretically estimate that zirconium oxide has excellent oxygen retention properties and experimentally verify that there is no significant oxygen diffusion leading to NbOx formation in the adjacent Nb electrode. We develop a top–down, subtractive fabrication process for Nb/Zr–ZrOx/Nb Josephson junctions, which enables scalability and large-scale production of superconducting electronics. Using cross-sectional scanning transmission electron microscopy, we experimentally find that depending on the Zr thickness, ZrOx tunnel barriers can be fully crystalline with chemically abrupt interfaces with niobium. Further analysis using electron energy loss spectroscopy reveals that ZrOx corresponds to tetragonal ZrO2. Room temperature characterization of fabricated junctions using Simmons’ model shows that ZrO2 exhibits a low tunnel barrier height, which is promising in merged-element transmon applications. Low temperature transport measurements reveal sub-gap structure, while the low-voltage sub-gap resistance remains in the megaohm range.
We present a full theoretical and experimental study of the dynamics and energy distribution of nonequilibrium quasiparticles in superconducting tunnel junctions (STJ's). STJ's are often used for single-photon spectrometers, where the numbers of quasiparticles excited by a photon provide a measure of the photon energy. The magnitude and fluctuations of the signal current in STJ detectors are in large part determined by the quasiparticle dynamics and energy distribution during the detection process. We use this as motivation to study the transport and energy distribution of nonequilibrium quasiparticles excited by x-ray photons in a lateral, imaging junction configuration. We present a full numerical model for the tunneling current of the major physical processes which determine the signal. We find that a diffusion framework models the quasiparticle dynamics well and that excited quasiparticles do not equilibrate to the lattice temperature during the time scales for tunneling. We extract physical time scales from the measured data, make comparisons with existing theories, and comment on implications for superconducting mesoscopic systems and single-photon detectors.
Low temperature scanning electron microscopy (LTSEM) offers the possibility for spatially resolved investigations of microwave properties of single Josephson junctions, superconducting striplines, resonators, and complex cryoelectric circuits during their operation. The spatial resolution of about 1 μm is at least two orders of magnitude better than the typical wavelength (≳100 μm in the elements) in the frequency range of interest (50–500 GHz). We demonstrate that LTSEM is a well suited tool for the experimental investigation of superconducting microwave devices and cryoelectronic circuits.
The latest generation of high quality, narrow gap, superconducting tunnel junctions (STJs) exhibits a steady-state and time-dependent behavior which cannot be described satisfactorily by previous treatments of nonequilibrium quasiparticle (qp) dynamics. These effects are particularly evident in experiments using STJs as detectors of photons, over the range from near infrared to x ray. In this paper, we present a detailed theoretical analysis of the spectral and temporal evolution of the nonequilibrium qp and phonon distributions in such STJs excited by single photons, over a wide range of excitation energy, bias voltage, and temperature. By solving the coupled set of kinetic equations describing the interacting excitations, we show that the nonequilibrium qp distribution created by the initial photoabsorption does not decay directly back to the initial undisturbed state in thermal equilibrium. Instead, it undergoes a rapid adiabatic relaxation to a long-lived, excited state, the spectral distribution of which is nonthermal, maintained by a balance between qp creation, recombination, and trapping. The model is able to describe successfully photoabsorption data taken on several different aluminum STJs, using a single set of parameters. Of particular note is the conclusion that the local traps responsible for qp loss are situated specifically in the region of Nb contacts.
Niobium thin films are key components of superconducting microwave resonators. Interest in these devices has increased dramatically because of their application in quantum systems. Despite tremendous effort to improve their performance, loss mechanisms are still not well understood. Nb/substrate and Nb/air interfaces are likely culprits in contributing to decoherence and ultimately limiting the performance of superconducting devices. Here, we investigate the Nb/substrate interface by studying the effect of hydrogen-passivated H:Si(111) substrates on the local superconducting properties of ∼40 nm thick Nb films compared to Nb films grown on typical Si(001) substrates. Specifically, low-temperature scanning tunneling microscopy and spectroscopy are employed to compare nanoscale material properties. The atomically flat monohydride H:Si(111) substrates are found to yield a smoother and less defective interface with the Nb film. Correspondingly, the Nb films grown on H:Si(111) substrates present more uniform superconducting properties and exhibit less quasiparticle broadening.