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Kitaygorsky, J., Komissarov, I., Jukna, A., Sobolewski, R., Minaeva, O., Kaurova, N., et al. (2006). Nanosecond, transient resistive state in two-dimensional superconducting stripes. In Proc. APS March Meeting (H38.13).
Abstract: We have observed, nanosecond-in-duration, transient voltage pulses, generated across two-dimensional (2-D) NbN stripes (width: 100--500 nm; thickness: 3.5--10 nm) of various lengths (1--500 μm), when the wires were completely isolated from the outside world, biased at currents close to the critical current, and kept at temperatures below the mean-field critical temperature Tco. In 2-D superconducting films, at temperatures below the Kosterlitz-Thouless transition, all vortices are bound and the resistance is zero. However, these vortices can get unbound when a large enough transport current is applied. The latter results in a transient resistive state, which manifests itself as spontaneous, 2.5--8-ns-long voltage pulses with the amplitude corresponding to the unbinding potential of a vortex pair. In our 100-nm-wide stripes, we have also observed the formation of phase slip centers (PSCs) at temperatures close to Tco, and a mixture of PSCs and unbound vortex-antivortex pairs at low temperatures.
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Kooi, J. W., Baselmans, J. J. A., Baryshev, A., Schieder, R., Hajenius, M., Gao, J. R., et al. (2006). Stability of heterodyne terahertz receivers. J. Appl. Phys., 100(6), 064904 (1 to 9).
Abstract: In this paper we discuss the stability of heterodyne terahertz receivers based on small volume NbN phonon cooled hot electron bolometers (HEBs). The stability of these receivers can be broken down in two parts: the intrinsic stability of the HEB mixer and the stability of the local oscillator (LO) signal injection scheme. Measurements show that the HEB mixer stability is limited by gain fluctuations with a 1∕f spectral distribution. In a 60MHz noise bandwidth this results in an Allan variance stability time of ∼0.3s. Measurement of the spectroscopic Allan variance between two intermediate frequency (IF) channels results in a much longer Allan variance stability time, i.e., 3s between a 2.5 and a 4.7GHz channel, and even longer for more closely spaced channels. This implies that the HEB mixer 1∕f noise is strongly correlated across the IF band and that the correlation gets stronger the closer the IF channels are spaced. In the second part of the paper we discuss atmospheric and mechanical system stability requirements on the LO-mixer cavity path length. We calculate the mixer output noise fluctuations as a result of small perturbations of the LO-mixer standing wave, and find very stringent mechanical and atmospheric tolerance requirements for receivers operating at terahertz frequencies.
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Koshelets, V. P., Borisov, V. B., Dmitriev, P. N., Ermakov, A. B., Filippenko, L. V., Khudchenko, A. V., et al. (2006). Integrated submillimeter receiver for TELIS. Joint International Workshop “Nanosensors and Arrays of Quantum Dots and Josephson Junctions for space applications”, 10th International Workshop “From Andreev Reflection to the Earliest Universe”, .
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Koshelets, V. P., Ermakov, A. B., Filippenko, L. V., Koryukin, O. V., Khudchenko, A. V., Sobolev, A. S., et al. (2006). Superconducting submm integrated receiver for TELIS. In J. Phys.: Conf. Ser. (Vol. 43, pp. 1377–1380).
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Koshelets, V. P., & Khudchenko, A. V. (2006). Analysis of spectral characteristics of a superconducting integrated receiver. J. Communications Technol. Electron., 51(5), 596–603.
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