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Register a new userSuperconducting THz sources with 12% power efficiency
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Added by
Vladimir M. Krasnov
Publication date
2021
fields
Physics
and research's language is
English
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Low power efficiency is one of the main problems of THz sources, colloquially known as the THz gap. In this work we present prototypes of THz devices based on whisker-crystals of a hightemperature superconductor Bi2Sr2CaCu2O8+d with a record high radiation power efficiency of 12% at a frequency of 4 THz. We employ various on- and off-chip detection techniques and, in particular, use the radiative cooling phenomenon for accurate evaluation of the emission power. We argue that such devices can be used for creation of tunable, monochromatic, continuous-wave, compact and power-efficient THz sources.
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The search for hydride compounds that exhibit high $T_c$ superconductivity has been extensively studied. Within the range of binary hydride compounds, the studies have been developed well including data-driven searches as a topic of interest. Toward the search for the ternary systems, the number of possible combinations grows rapidly, and hence the power of data-driven search gets more prominent. In this study, we constructed various regression models to predict $T_c$ for ternary hydride compounds and found the extreme gradient boosting (XGBoost) regression giving the best performance. The best performed regression predicts new promising candidates realizing higher $T_c$, for which we further identified their possible crystal structures. Confirming their lattice and thermodynamical stabilities, we finally predicted new ternary hydride superconductors, YKH$_{12}$ [$C2/m$ (No.12), $T_c$=143.2 K at 240 GPa] and LaKH$_{12}$ [$Rbar{3}m$ (No.166), $T_c$=99.2 K at 140 GPa] from first principles.
Terahertz phonon spectroscopy studies of bismuth cuprates are overviewed.
Thin-film superconductors with thickness 30 to 500 nm are used as non-equilibrium quantum detectors for photons, phonons or more exotic particles. One of the most basic questions in determining their limiting sensitivity is the efficiency with which the quanta of interest couple to the detected quasiparticles. As low temperature superconducting resonators, thin-films are attractive candidates for producing quantum-sensitive arrayable sensors and the readout uses an additional microwave probe. We have calculated the quasiparticle generation efficiency eta_s for low energy photons in a representative, clean thin-film superconductor (Al) operating well-below its superconductingtransition temperature as a function of film thickness, within the framework of the coupled kineticequations described by Chang and Scalapino.[J. J. Chang and D. J. Scalapino, J. Low Temp. Phys. 31, 1 (1978)]. We have also included the effect of a lower frequency probe. We show that phonon loss from the thin-film reduces eta_s by as much as 40% compared to earlier models that considered relatively thick films or infinite volumes. We also show that the presence of the probe and signal enhances the generation efficiency slightly. We conclude that the ultimate limiting noise equivalent power of this class of detector is determined by the thin-film geometry.
We have used a neon focused-ion-beam to fabricate both nanoscale Nb Dayem bridges and NbN phase-slip nanowires located at the short-circuited end of quarter-wavelength coplanar waveguide resonators. The Dayem bridge devices show flux-tunability and intrinsic quality factor exceeding 10,000 at 300 mK up to local fields of at least 60 mT. The NbN nanowires show signatures of incoherent quantum tunnelling of flux at 300 mK.
We observe a broadband chaotic signal of Terahertz frequency emitted from a superconducting junction. The generated radiation has a wide spectrum reaching 0.7 THz and power sufficient to drive on-chip circuit elements. To our knowledge, this is the first experimental observation of a high-frequency chaotic signal emitted by a superconducting system which lies inside the Terahertz gap. Our experimental finding is fully confirmed by the numerical modeling based on the microscopic theory and reveals the unrealized potential of superconducting systems in chaos-based Terahertz communication, fast generation of true random numbers and non-invasive Terahertz spectroscopy applicable to physical, chemical and biological systems.
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