Electron energy relaxation in disordered superconducting NbN films

We report onthe energy relaxation of electrons studied by means of magnetoconductance and photoresponse in a series of superconducting NbN film with thickness in the range from 3 to 33 nm. The inelastic scattering rate of electrons on phonons obeys Tntemperature dependence where the exponent is in the range ????≈3.2÷3.8and shows no systematically dependence on the degree of disorder. At 11K electron-phonon scattering times are in the range11.9 -17.5 ps.We show that in the studied NbN films the Debye temperature and the densityof phononstatesare both reduced with respect to bulk material. In the thinnest studied films reduced density of states along with the phonon trapping slowsdown the energy relaxationofelectrons by afactor of 4 as compared to the prediction of the tree dimensional phonon mode

Electron energy relaxation in disordered superconducting NbN films

We report on the inelastic-scattering rate of electrons on phonons and relaxation of electron energy studied by means of magnetoconductance, and photoresponse, respectively, in a series of strongly disordered superconducting NbN films. The studied films with thicknesses in the range from 3 to 33 nm are characterized by different Ioffe-Regel parameters but an almost constant product q_Tl(q_T is the wave vector of thermal phonons and l is the elastic mean free path of electrons). In the temperature range 14-30 K, the electron-phonon scattering rates obey temperature dependencies close to the power law 1/\tau_{e-ph} \sim T^n with the exponents n = 3.2-3.8. We found that in this temperature range \tau_{e-ph} and n of studied films vary weakly with the thickness and square resistance. At 10 K electron-phonon scattering times are in the range 11.9-17.5 ps. The data extracted from magnetoconductance measurements were used to describe the experimental photoresponse with the two-temperature model. For thick films, the photoresponse is reasonably well described without fitting parameters, however, for thinner films, the fit requires a smaller heat capacity of phonons. We attribute this finding to the reduced density of phonon states in thin films at low temperatures. We also show that the estimated Debye temperature in the studied NbN films is noticeably smaller than in bulk material.Comment: 23 pages, 6 figure

Sperm collection and storage for the sustainable management of amphibian biodiversity

Current rates of biodiversity loss pose an unprecedented challenge to the conservation community, particularly with amphibians and freshwater fish as the most threatened vertebrates. An increasing number of environmental challenges, including habitat loss, pathogens, and global warming, demand a global response toward the sustainable management of ecosystems and their biodiversity. Conservation Breeding Programs (CBPs) are needed for the sustainable management of amphibian species threatened with extinction. CBPs support species survival while increasing public awareness and political influence. Current CBPs only cater for 10% of the almost 500 amphibian species in need. However, the use of sperm storage to increase efficiency and reliability, along with an increased number of CBPs, offer the potential to significantly reduce species loss. The establishment and refinement of techniques over the last two decades, for the collection and storage of amphibian spermatozoa, gives confidence for their use in CBPs and other biotechnical applications. Cryopreserved spermatozoa has produced breeding pairs of frogs and salamanders and the stage is set for Lifecycle Proof of Concept Programs that use cryopreserved sperm in CBPs along with repopulation, supplementation, and translocation programs. The application of cryopreserved sperm in CBPs, is complimentary to but separate from archival gene banking and general cell and tissue storage. However, where appropriate amphibian sperm banking should be integrated into other global biobanking projects, especially those for fish, and those that include the use of cryopreserved material for genomics and other research. Research over a broader range of amphibian species, and more uniformity in experimental methodology, is needed to inform both theory and application. Genomics is revolutionising our understanding of biological processes and increasingly guiding species conservation through the identification of evolutionary significant units as the conservation focus, and through revealing the intimate relationship between evolutionary history and sperm physiology that ultimately affects the amenability of sperm to refrigerated or frozen storage. In the present review we provide a nascent phylogenetic framework for integration with other research lines to further the potential of amphibian sperm banking

Cold-electron bolometer array integrated with a 350 GHz cross-slot antenna

Two series/parallel arrays of Cold-Electron Bolometers (CEB) with Superconductor-Insulator-Normal (SIN) tunnel junctions were integrated in orthogonal ports of a cross-slot antenna. The receiving system was designed for polarisation measurements in a 350 GHz frequency band with JFET readout at the BOOMERanG-FG balloon telescope. Each orthogonal array consists of 10 cold-electron bolometers connected in parallel for RF signal and in series for DC signal. The array was designed to increase the output resistance by a factor of 102 in comparison to a single CEB, for matching with JFET readout while maintaining the same conditions for RF coupling. The dynamic resistance of such array is 1 M5 at the bias point of maximal response. For the input microwave signal bolometers are connected in parallel. This provides matching to the 30 input impedance of a cross-slot antenna on Si substrate. The array of bolometers has a saturation power 10 times higher than a single bolometer. This significantly increases the dynamic range. With a measured temperature response of 8.8 μV/mK, a total absorber volume of 0.08 μm3, and an output noise of about 11 nV/Hz1/2, we estimated the dark electrical noise equivalent power as NEP=6*10-18 W/Hz1/2 at 280 mK. The optical response was measured using both hot/cold loads and a backward wave oscillator as sources of radiation

Cold-electron bolometer array integrated with a 350 GHz cross-slot antenna

Two series/parallel arrays of Cold-Electron Bolometers (CEB) with Superconductor-Insulator-Normal (SIN) tunnel junctions were integrated in orthogonal ports of a cross-slot antenna. The receiving system was designed for polarisation measurements in a 350 GHz frequency band with JFET readout at the BOOMERanG-FG balloon telescope. Each orthogonal array consists of 10 cold-electron bolometers connected in parallel for RF signal and in series for DC signal. The array was designed to increase the output resistance by a factor of 102 in comparison to a single CEB, for matching with JFET readout while maintaining the same conditions for RF coupling. The dynamic resistance of such array is 1 M5 at the bias point of maximal response. For the input microwave signal bolometers are connected in parallel. This provides matching to the 30 input impedance of a cross-slot antenna on Si substrate. The array of bolometers has a saturation power 10 times higher than a single bolometer. This significantly increases the dynamic range. With a measured temperature response of 8.8 μV/mK, a total absorber volume of 0.08 μm3, and an output noise of about 11 nV/Hz1/2, we estimated the dark electrical noise equivalent power as NEP=6*10-18 W/Hz1/2 at 280 mK. The optical response was measured using both hot/cold loads and a backward wave oscillator as sources of radiation

Electron energy relaxation in disordered superconducting NbN films

We report on the inelastic-scattering rate of electrons on phonons and relaxation of electron energy studied by means of magnetoconductance, and photoresponse, respectively, in a series of strongly disordered superconducting NbN films. The studied films with thicknesses in the range from 3 to 33 nm are characterized by different Ioffe-Regel parameters but an almost constant product qTl (qT is the wave vector of thermal phonons and l is the elastic mean free path of electrons). In the temperature range 14–30 K, the electron-phonon scattering rates obey temperature dependencies close to the power law 1/τe−ph∼Tn with the exponents n≈3.2–3.8. We found that in this temperature range τe−ph and n of studied films vary weakly with the thickness and square resistance. At 10 K electron-phonon scattering times are in the range 11.9–17.5 ps. The data extracted from magnetoconductance measurements were used to describe the experimental photoresponse with the two-temperature model. For thick films, the photoresponse is reasonably well described without fitting parameters, however, for thinner films, the fit requires a smaller heat capacity of phonons. We attribute this finding to the reduced density of phonon states in thin films at low temperatures. We also show that the estimated Debye temperature in the studied NbN films is noticeably smaller than in bulk material

Helicity-Sensitive Plasmonic Terahertz Interferometer

Plasmonic interferometry is a rapidly growing area of research with a huge potential for applications in the terahertz frequency range. In this Letter, we explore a plasmonic interferometer based on graphene field effect transistor connected to specially designed antennas. As a key result, we observe helicity- and phase-sensitive conversion of circularly polarized radiation into dc photovoltage caused by the plasmon-interference mechanism: two plasma waves, excited at the source and drain part of the transistor, interfere inside the channel. The helicity-sensitive phase shift between these waves is achieved by using an asymmetric antenna configuration. The dc signal changes sign with inversion of the helicity. A suggested plasmonic interferometer is capable of measuring the phase difference between two arbitrary phase-shifted optical signals. The observed effect opens a wide avenue for phase-sensitive probing of plasma wave excitations in two-dimensional materials