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Seliverstov, S., Maslennikov, S., Ryabchun, S., Finkel, M., Klapwijk, T. M., Kaurova, N., et al. (2015). Fast and sensitive terahertz direct detector based on superconducting antenna-coupled hot electron bolometer. IEEE Trans. Appl. Supercond., 25(3), 2300304.
Abstract: We characterize superconducting antenna-coupled hot-electron bolometers for direct detection of terahertz radiation operating at a temperature of 9.0 K. The estimated value of responsivity obtained from lumped-element theory is strongly different from the measured one. A numerical calculation of the detector responsivity is developed, using the Euler method, applied to the system of heat balance equations written in recurrent form. This distributed element model takes into account the effect of nonuniform heating of the detector along its length and provides results that are in better agreement with the experiment. At a signal frequency of 2.5 THz, the measured value of the optical detector noise equivalent power is 2.0 × 10-13 W · Hz-0.5. The value of the bolometer time constant is 35 ps. The corresponding energy resolution is about 3 aJ. This detector has a sensitivity similar to that of the state-of-the-art sub-millimeter detectors operating at accessible cryogenic temperatures, but with a response time several orders of magnitude shorter.
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Hajenius, M., Baselmans, J. J. A., Baryshev, A., Gao, J. R., Klapwijk, T. M., Kooi, J. W., et al. (2006). Full characterization and analysis of a terahertz heterodyne receiver based on a NbN hot electron bolometer. J. Appl. Phys., 100(7), 074507.
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Floet, D. W., Baselmans, J. J. A., Klapwijk, T. M., & Gao, J. R. (1998). Resistive transition of niobium superconducting hot-electron bolometer mixers. Appl. Phys. Lett., 73(19), 2826.
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Kardakova, A., Finkel, M., Morozov, D., Kovalyuk, V., An, P., Dunscombe, C., et al. (2013). The electron-phonon relaxation time in thin superconducting titanium nitride films. Appl. Phys. Lett., 103(25), 252602 (1 to 4).
Abstract: We report on the direct measurement of the electron-phonon relaxation time, τeph, in disordered TiN films. Measured values of τeph are from 5.5 ns to 88 ns in the 4.2 to 1.7 K temperature range and consistent with a T−3 temperature dependence. The electronic density of states at the Fermi level N0 is estimated from measured material parameters. The presented results confirm that thin TiN films are promising candidate-materials for ultrasensitive superconducting detectors.
The work was supported by the Ministry of Education and Science of the Russian Federation, Contract No. 14.B25.31.0007 and by the RFBR Grant No. 13-02-91159.
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Yang, Y., Fedorov, G., Shafranjuk, S. E., Klapwijk, T. M., Cooper, B. K., Lewis, R. M., et al. (2015). Electronic transport and possible superconductivity at Van Hove singularities in carbon nanotubes. Nano Lett., 15(12), 7859–7866.
Abstract: Van Hove singularities (VHSs) are a hallmark of reduced dimensionality, leading to a divergent density of states in one and two dimensions and predictions of new electronic properties when the Fermi energy is close to these divergences. In carbon nanotubes, VHSs mark the onset of new subbands. They are elusive in standard electronic transport characterization measurements because they do not typically appear as notable features and therefore their effect on the nanotube conductance is largely unexplored. Here we report conductance measurements of carbon nanotubes where VHSs are clearly revealed by interference patterns of the electronic wave functions, showing both a sharp increase of quantum capacitance, and a sharp reduction of energy level spacing, consistent with an upsurge of density of states. At VHSs, we also measure an anomalous increase of conductance below a temperature of about 30 K. We argue that this transport feature is consistent with the formation of Cooper pairs in the nanotube.
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