-
Imaging the Superconducting Proximity Effect in S-S'-S Transition Edge Sensors
Authors:
Austin R. Kaczmarek,
Samantha Walker,
Jason Austermann,
Douglas Bennett,
W. Bertrand Doriese,
Shannon M. Duff,
Johannes Hubmayr,
Kelsey Morgan,
Michael D. Niemack,
Dan Schmidt,
Daniel Swetz,
Joel Ullom,
Joel Weber,
Katja C. Nowack
Abstract:
Proximity effects at superconducting interfaces, between different superconductors (S-S') or between superconductors and normal metals (S-N), are fundamental to the performance of superconducting electronics, yet only few experiments have directly probed the spatial structure of proximity effects within a device. This is particularly relevant for transition edge sensors (TESs), where the interplay…
▽ More
Proximity effects at superconducting interfaces, between different superconductors (S-S') or between superconductors and normal metals (S-N), are fundamental to the performance of superconducting electronics, yet only few experiments have directly probed the spatial structure of proximity effects within a device. This is particularly relevant for transition edge sensors (TESs), where the interplay of direct and inverse proximity effects governs detector sensitivity. Here, we use scanning superconducting interference device (SQUID) susceptometry to directly image the local diamagnetic response in functional S-S'-S TES structures. We resolve long range proximity coupling extending over tens of micrometers, revealing that the local transition temperature is dramatically tuned by neighboring regions, being either enhanced by superconducting (S) leads or suppressed by normal metal (N) contacts. Our observations are quantitatively supported by Ginzburg Landau modeling of the device geometry and calculations of the temperature dependent diamagnetism based on self-consistent Usadel equations. By providing spatially resolved measurements of the interplay of proximity effects in TES devices, this work establishes a framework for understanding and controlling superconducting states in heterogeneous superconducting structures.
△ Less
Submitted 22 February, 2026;
originally announced February 2026.
-
Can slow recombination in ordered superconductors explain the excess quasiparticle population?
Authors:
Eva Gurra,
Douglas A. Bennett,
Shannon M. Duff,
Michael R. Vissers,
Joel N. Ullom
Abstract:
An excess density of quasiparticles is widely observed in superconducting films. This excess causes performance degradation in a variety of superconducting devices, including decoherence in qubits. In this Letter, we evaluate the hypothesis of [1] that the quasiparticle excess is caused by anomalously slow recombination at low quasiparticle densities due to localization in sub-gap states. We probe…
▽ More
An excess density of quasiparticles is widely observed in superconducting films. This excess causes performance degradation in a variety of superconducting devices, including decoherence in qubits. In this Letter, we evaluate the hypothesis of [1] that the quasiparticle excess is caused by anomalously slow recombination at low quasiparticle densities due to localization in sub-gap states. We probe the density of states in aluminum and niobium films using current-voltage measurements of tunnel junctions and extract upper bounds on the energy scales of the sub-gap states and gap smearing. With these parameters, we evaluate the recombination times predicted by [1] and find that slow recombination is not predicted to occur at observed quasiparticle densities in aluminumand niobium-based superconducting devices. These results suggest that the quasiparticle excess in ordered superconductors is primarily due to non-thermal sources of quasiparticle generation and not slow recombination.
△ Less
Submitted 3 July, 2025;
originally announced July 2025.
-
Direct Imaging of Transition-Edge Sensors with Scanning SQUID Microscopy
Authors:
Samantha Walker,
Austin Kaczmarek,
Jason Austermann,
Douglas Bennett,
Shannon M. Duff,
Johannes Hubmayr,
Ben Keller,
Kelsey Morgan,
Colin C. Murphy,
Daniel Swetz,
Joel Ullom,
Michael D. Niemack,
Katja C. Nowack
Abstract:
Significant advancements have been made in understanding the physics of transition-edge sensors (TESs) over the past decade. However, key questions remain, particularly a detailed understanding of the current-dependent resistance of these detectors when biased within their superconducting transition. We use scanning superconducting quantum interference device (SQUID) microscopy (SSM) to image the…
▽ More
Significant advancements have been made in understanding the physics of transition-edge sensors (TESs) over the past decade. However, key questions remain, particularly a detailed understanding of the current-dependent resistance of these detectors when biased within their superconducting transition. We use scanning superconducting quantum interference device (SQUID) microscopy (SSM) to image the local diamagnetic response of aluminum-manganese alloy (Al-Mn) transition-edge sensors (TESs) near their critical temperature of approximately 175 mK. By doing so, we gain insights into how the device dimensions influence TES transition width, which in turn affects device operation and informs optimal device design. Our images reveal that the Al-Mn thin film near the niobium (Nb) leads exhibits an excess diamagnetic response at temperatures several milli-Kelvin (mK) higher than the bulk of the film farther from the contacts. A possible origin of this behavior is a longitudinal proximity effect between the Nb and Al-Mn where the TES acts as a weak link between superconducting leads. We discuss how this effect shapes the temperature dependence of the resistance as the spacing between the leads decreases. This work demonstrates that magnetic imaging with SSM is a powerful tool for local characterization of superconducting detectors.
△ Less
Submitted 2 October, 2024;
originally announced October 2024.
-
Tile-and-trim micro-resonator array fabrication optimized for high multiplexing factors
Authors:
Christopher M. McKenney,
Jason E. Austermann,
Jim Beall,
Bradley Dober,
Shannon M. Duff,
Jiansong Gao,
Gence C. Hilton,
Johannes Hubmayr,
Dale Li,
Joel N. Ullom,
Jeff Van Lanen,
Michael R. Vissers
Abstract:
We present a superconducting micro-resonator array fabrication method that is scalable, reconfigurable, and has been optimized for high multiplexing factors. The method uses uniformly sized tiles patterned on stepper photolithography reticles as the building blocks of an array. We demonstrate this technique on a 101-element microwave kinetic inductance detector (MKID) array made from a titanium-ni…
▽ More
We present a superconducting micro-resonator array fabrication method that is scalable, reconfigurable, and has been optimized for high multiplexing factors. The method uses uniformly sized tiles patterned on stepper photolithography reticles as the building blocks of an array. We demonstrate this technique on a 101-element microwave kinetic inductance detector (MKID) array made from a titanium-nitride superconducting film. Characterization reveals 1.5\% maximum fractional frequency spacing deviations caused primarily by material parameters that vary smoothly across the wafer. However, local deviations exhibit a Gaussian distribution in fractional frequency spacing with a standard deviation of $2.7 \times 10^{-3}$. We exploit this finding to increase the yield of the BLAST-TNG $250 \; μ\text{m}$ production wafer by placing resonators in the array close in both physical and frequency space. This array consists of 1836 polarization-sensitive MKIDs wired in three multiplexing groups. We present the array design and show that the achieved yield is consistent with our model of frequency collisions and is comparable to what has been achieved in other low temperature detector technologies.
△ Less
Submitted 12 March, 2018;
originally announced March 2018.
-
Hotspot Relaxation Dynamics in a Current Carrying Superconductor
Authors:
F. Marsili,
M. J. Stevens,
A. Kozorezov,
V. B. Verma,
Colin Lambert,
J. A. Stern,
R. Horansky,
S. Dyer,
S. Duff,
D. P. Pappas,
A. Lita,
M. D. Shaw,
R. P. Mirin,
S. W. Nam
Abstract:
We experimentally studied the dynamics of optically excited hotspots in current carrying WSi superconducting nanowires as a function of bias current, bath temperature and excitation wavelength. We discovered that: (1) the hotspot relaxation is a factor of ~ 4 slower in WSi than in NbN; (2) the hotspot relaxation time depends on bias current, and (3) the current dependence of the hotspot relaxation…
▽ More
We experimentally studied the dynamics of optically excited hotspots in current carrying WSi superconducting nanowires as a function of bias current, bath temperature and excitation wavelength. We discovered that: (1) the hotspot relaxation is a factor of ~ 4 slower in WSi than in NbN; (2) the hotspot relaxation time depends on bias current, and (3) the current dependence of the hotspot relaxation time changes with temperature and wavelength. We explained all of these effects with a model based on quasi particle recombination.
△ Less
Submitted 9 June, 2015;
originally announced June 2015.
-
Proximity-Coupled Ti/TiN Multilayers for use in Kinetic Inductance Detectors
Authors:
Michael R. Vissers,
Jiansong Gao,
Martin Sandberg,
Shannon M. Duff,
David S. Wisbey,
Kent D. Irwin,
David P. Pappas
Abstract:
We apply the superconducting proximity effect in TiN/Ti multi-layer films to tune the critical temperature, Tc, to within 10 mK with high uniformity (less than 15 mK spread) across a 75 mm wafer. Reproducible Tc's are obtained from 0.8 - 2.5 K. These films had high resistivities, > 100 uOhm-cm and internal quality factors for resonators in the GHz range on the order of 100k and higher. Both trilay…
▽ More
We apply the superconducting proximity effect in TiN/Ti multi-layer films to tune the critical temperature, Tc, to within 10 mK with high uniformity (less than 15 mK spread) across a 75 mm wafer. Reproducible Tc's are obtained from 0.8 - 2.5 K. These films had high resistivities, > 100 uOhm-cm and internal quality factors for resonators in the GHz range on the order of 100k and higher. Both trilayers of TiN/Ti/TiN and thicker superlattice films were prepared, demonstrating a highly controlled process for films over a wide thickness range. Detectors were fabricated and showed single photon resolution at 1550 nm. The high uniformity and controllability coupled with the high quality factor, kinetic inductance, and inertness of TiN make these films ideal for use in frequency multiplexed kinetic inductance detectors and other potential applications such as nanowire detectors, transition edge sensors and associated quantum information applications.
△ Less
Submitted 21 September, 2012;
originally announced September 2012.