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Samsonova, A. S.; Zolotov, P. I.; Baeva, E. M.; Lomakin, A. I.; Titova, N. A.; Kardakova, A. I.; Goltsman, G. N. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Signatures of surface magnetic disorder in niobium films |
Type ![sorted by Type field, descending order (down)](img/sort_desc.gif) |
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Year |
2021 |
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IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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31 |
Issue |
5 |
Pages |
1-5 |
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Nb films |
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We present our studies on the evolution of the normal and superconducting properties with thickness of thin Nb films with a low level of non-magnetic disorder ( kFl≈150 for the thickest film in the set). The analysis of the superconducting behavior points to the presence of magnetic moments, hidden in the native oxide on the surface of Nb films. Using the Abrikosov-Gorkov theory, we obtain the density of surface magnetic moments of 1013 cm −2 , which is in agreement with the previously reported data for Nb films. |
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1051-8223 |
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1792 |
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Peltonen, J. T.; Astafiev, O. V.; Korneeva, Y. P.; Voronov, B. M.; Korneev, A. A.; Charaev, I. M.; Semenov, A. V.; Golt'sman, G. N.; Ioffe, L. B.; Klapwijk, T. M.; Tsai, J. S. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Coherent flux tunneling through NbN nanowires |
Type ![sorted by Type field, descending order (down)](img/sort_desc.gif) |
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Year |
2013 |
Publication |
Phys. Rev. B |
Abbreviated Journal |
Phys. Rev. B |
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88 |
Issue |
22 |
Pages |
220506 (1 to 5) |
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NbN nanowires |
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We demonstrate evidence of coherent magnetic flux tunneling through superconducting nanowires patterned in a thin highly disordered NbN film. The phenomenon is revealed as a superposition of flux states in a fully metallic superconducting loop with the nanowire acting as an effective tunnel barrier for the magnetic flux, and reproducibly observed in different wires. The flux superposition achieved in the fully metallic NbN rings proves the universality of the phenomenon previously reported for InOx. We perform microwave spectroscopy and study the tunneling amplitude as a function of the wire width, compare the experimental results with theories, and estimate the parameters for existing theoretical models. |
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1098-0121 |
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1369 |
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Zhang, W.; Miao, W.; Li, S. L.; Zhou, K. M.; Shi, S. C.; Gao, J. R.; Goltsman, G. N. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Measurement of the spectral response of spiral-antenna coupled superconducting hot electron bolometers |
Type ![sorted by Type field, descending order (down)](img/sort_desc.gif) |
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2013 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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23 |
Issue |
3 |
Pages |
2300804-2300804 |
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NbN HEB detector |
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Measured spectral response of spiral-antenna coupled superconducting hot electron bolometers (HEBs) often drops dramatically at frequencies that are still within the frequency range of interest (e.g., ~ 5 THz). This is inconsistent with the implied low receiver noise temperatures from the same measurements. To understand this discrepancy, we exhaustively test and calibrate the thermal sources used in Fourier transform spectrometer measurements. We first investigate the absolute emission spectrum of high-pressure Hg arc lamp, then measure the spectral response of two spiral-antenna coupled NbN HEBs with a Martin-Puplett interferometer as spectrometer and 77 K blackbody as broadband signal source. The measured absolute emission spectrum of Hg arc lamp is proportional to frequency, corresponding to an equivalent blackbody temperature of 4000 K at 1 THz, 1500 K at 3 THz, and 800 K at 5 THz, respectively. Measured spectral response of spiral-antenna coupled NbN HEBs, corrected for air absorption, is nearly flat in the frequency range of 0.5-4 THz, consistent with simulated coupling efficiency between HEB and spiral-antenna. These results explain the discrepancy, and prove that spiral-antenna coupled superconducting NbN HEBs work well in a wide frequency range. In addition, this calibration method and these results are broadly applicable to other quasi-optical THz receivers. |
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1051-8223 |
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1371 |
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Shurakov, A.; Tong, C.-Y. E.; Blundell, R.; Kaurova, N.; Voronov, B.; Gol'tsman, G. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Microwave stabilization of a HEB mixer in a pulse-tube cryocooler |
Type ![sorted by Type field, descending order (down)](img/sort_desc.gif) |
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Year |
2013 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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Volume |
23 |
Issue |
3 |
Pages |
1501504-1501504 |
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NbN HEB mixers |
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We report the results of our study of the stability of an 800 GHz hot electron bolometer (HEB) mixer cooled with a pulse-tube cryocooler. Pulse-tube cryocoolers introduce temperature fluctuations as well as mechanical vibrations at a frequency of ~1 Hz, both of which can cause receiver gain fluctuations at that frequency. In our system, the motor of the cryocooler was separated from the cryostat to minimize mechanical vibrations, leaving thermal effects as the dominant source of the receiver gain fluctuations. We measured root mean square temperature variations of the 4 K stage of ~7 mK. The HEB mixer was pumped by a solid state local oscillator at 810 GHz. The root mean square current fluctuations at the low noise operating point (1.50 mV, 56.5 μA) were ~0.12 μA, and were predominantly due to thermal fluctuations. To stabilize the bias current, microwave radiation was injected to the HEB mixer. The injected power level was set by a proportional-integral-derivative controller, which completely compensates for the bias current oscillations induced by the pulse-tube cryocooler. Significant improvement in the Allan variance of the receiver output power was obtained, and an Allan time of 5 s was measured. |
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1051-8223 |
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1372 |
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Lusche, R.; Semenov, A.; Il'in, K.; Korneeva, Y.; Trifonov, A.; Korneev, A.; Hubers, H.; Siegel, M.; Gol'tsman, G. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Effect of the wire width and magnetic field on the intrinsic detection efficiency of superconducting nanowire single-photon detectors |
Type ![sorted by Type field, descending order (down)](img/sort_desc.gif) |
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Year |
2013 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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Volume |
23 |
Issue |
3 |
Pages |
2200205-2200205 |
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Keywords |
SSPD, SNSPD |
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We present thorough measurements of the intrinsic detection efficiency in the wavelength range from 350 to 2500 nm for meander-type TaN and NbN superconducting nanowire single-photon detectors with different widths of the nanowire. The width varied from 70 nm to 130 nm. The open-beam configuration allowed us to accurately normalize measured spectra and to extract the intrinsic detection efficiency. For detectors from both materials the intrinsic detection efficiency at short wavelengths amounts at 100% and gradually decreases at wavelengths larger than the specific cut-off wavelengths, which decreases with the width of the nanowire. Furthermore, we show that applying weak magnetic fields perpendicular to the meander plane decreases the smallest detectable photon flux. |
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1376 |
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