Microscopic interpretation of the Dynes formula for the tunneling density of states

Herman, František; Hlubina, R.

doi:10.1103/physrevb.94.144508

Cited by 58 publications

(41 citation statements)

References 23 publications

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“…31 Physically, this parameter represents a Cooper-pair breaking scattering process caused by impurities in the film, which have the effect of modifying both the temperature dependence of the superconducting gap energy and the complex conductivity. 32 The extended Mattis-Bardeen equations fit well to the hafnium data when we also allow the zero temperature gap energy, ∆ 0 , to vary. For hafnium, we find Γ/∆ 0 = 0.006 and ∆ 0 = 1.5k B T c .…”

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confidence: 79%

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Zobrist

Coiffard

Bumble

et al. 2019

Applied Physics Letters

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We report on the design and performance of Microwave Kinetic Inductance Detectors (MKIDs) sensitive to single photons in the optical to near-infrared range using hafnium as the sensor material. Our test device had a superconducting transition temperature of 395 mK and a room temperature normal state resistivity of 97 µΩ cm with an RRR = 1.6. Resonators on the device displayed internal quality factors of around 200 000. Similar to the analysis of MKIDs made from other highly resistive superconductors, we find that modeling the temperature response of the detector requires an extra broadening parameter in the superconducting density of states. Finally, we show that this material and design is compatible with a full-array fabrication process which resulted in pixels with decay times of about 40 µs and resolving powers of ∼9 at 800 nm.Optical and near-IR (OIR) MKIDs are superconducting sensors capable of measuring the arrival time and energy of optical to near-infrared photons. 1 They are less sensitive to false counts and radiation damage 2 than semiconductor devices operating in the same wavelength range and can achieve higher readout speeds. Moreover, each MKID is a high quality factor resonator which allows for natural frequency domain multiplexing and distinguishes the technology from other superconducting detectors. These advantages make arrays of OIR MKIDs useful as astrophysics cameras focusing on timedomain astronomy 3-5 and high contrast imaging. 6-8 To date, commissioned instruments have used either nonstoichiometric titanium nitride or platinum silicide alloys as the photon-sensitive material in the resonators and have achieved resolving powers, R = E/∆E, of up to 8 at 800 nm. 9 This resolving power has been shown to be limited equally by stationary noise, generated by two-level systems (TLS) in the device and amplifiers in the readout chain, as well as an intrinsic variance in the photon signal pulse height, likely caused by phonon escape from the superconductor to the substrate during the initial photon energy down-conversion. 10

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confidence: 79%

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Zobrist

Coiffard

Bumble

et al. 2019

Applied Physics Letters

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“…In the same measurement we still observed some correlation of the absolute uctuation strength with Γ Φ . Our explanation is Appendix G: Other decoherence sources Increased quasiparticle density due to pair-breaking by ingap states, as observed in Pb 0.9 Bi 0.1 junctions [54] or thin MoC lms [55,56], could increase the qubit's relaxation rate. To our knowledge, no evidence of excessive pair breaking due to in-gap states has been reported for material systems like our sample at 20 mK.…”

Section: Appendix A: Experimental Detailsmentioning

confidence: 99%

Correlating Decoherence in Transmon Qubits: Low Frequency Noise by Single Fluctuators

Schlör¹,

Lisenfeld²,

Müller³

et al. 2019

Phys. Rev. Lett.

176

138

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We report on long-term measurements of a highly coherent, non-tunable superconducting transmon qubit, revealing low-frequency burst noise in coherence times and qubit transition frequency. We achieve this through a simultaneous measurement of the qubit's relaxation and dephasing rate as well as its resonance frequency. The analysis of correlations between these parameters yields information about the microscopic origin of the intrinsic decoherence mechanisms in Josephson qubits. Our results are consistent with a small number of microscopic two-level systems located at the edges of the superconducting lm, which is further con rmed by a spectral noise analysis. arXiv:1901.05352v2 [cond-mat.supr-con]

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“…As shown in Ref. 6, the magnitude of the gap ∆ of a Dynes superconductor is controlled by the pair-breaking scattering rate Γ, and in the BCS model with coupling constant λ and cutoff frequency Ω it can be found by solving the self-consistent equation…”

Section: Optical Conductivity: Dynes Superconductorsmentioning

confidence: 99%

“…(1) has to be taken so that its imaginary part is positive and we keep this convention throughout this paper. The microscopic origin of the Dynes formula had been unclear for a long time, but in a recent paper 6 we have shown that the tunneling density of states described by Eq. (1) is realized in systems with pair-breaking classical disorder, provided that the pair-breaking potentials have a Lorentzian distribution with width Γ; we did not need to make any assumptions about the nature of the pairconserving disorder.…”

Section: Introductionmentioning

confidence: 99%

“…16,17 are applicable only to superconductors with not too large density of magnetic impurities, and therefore they can not describe electrodynamics of the Dynes superconductors with a dense and broad distribution of pair-breaking fields. 6 To the best of our knowledge, the Dynes phenomenology has been taken seriously only in the very recent paper Ref. 14, where Nam's dirty-limit formula for σ(ω) was evaluated assuming that the tunneling density of states is given by Eq.…”

Section: Introductionmentioning

confidence: 99%

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Electromagnetic properties of impure superconductors with pair-breaking processes

Herman

Hlubina

2017

Phys. Rev. B

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Recently a generic model has been proposed for the single-particle properties of gapless superconductors with simultaneously present pair-conserving and pair-breaking impurity scattering (the so-called Dynes superconductors). Here we calculate the optical conductivity of the Dynes superconductors. Our approach is applicable for all disorder strengths from the clean up to the dirty limit and for all relative ratios of the two types of scattering, nevertheless the complexity of our description is equivalent to that of the widely used Mattis-Bardeen theory. We identify two optical fingerprints of the Dynes superconductors: (i) the presence of two absorption edges and (ii) a finite absorption at vanishing frequencies even at the lowest temperatures. We demonstrate that the recent anomalous optical data on thin MoN films can be reasonably fitted by our theory.

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Microscopic interpretation of the Dynes formula for the tunneling density of states

Cited by 58 publications

References 23 publications

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Correlating Decoherence in Transmon Qubits: Low Frequency Noise by Single Fluctuators

Electromagnetic properties of impure superconductors with pair-breaking processes

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