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- Chesnokov, A., et al.
(författare)
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The local atomic structure and thermoelectric properties of Ir-doped ZnO : hybrid DFT calculations and XAS experiments
- 2021
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 9:14, s. 4948-4960
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Tidskriftsartikel (refereegranskat)abstract
- We combined the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments in the study of the local atomic structure around Ir ions in ZnO thin films with different iridium content. This was then used in the first principles analysis of the thermoelectric properties of material. The emphasis has been put on the conditions for a positive Seebeck coefficient and p-type electrical conductivity as the functions of the Fermi level. We studied both computationally and experimentally several possible IrOxpolyhedra (complexes) with a different number of surrounding oxygens and Ir oxidation states, including those with the formation of peroxide ions (O22−). In particular, octahedral coordination of iridium ions was identified by reverse Monte Carlo (RMC) simulations of the Ir L3-edge EXAFS spectra of ZnO:Ir thin films as the predominant complex, which is supported by the calculated lowest interstitial oxygen incorporation energies. All the calculated IrOx(x= 4, 5, 6) complexes, regardless of Ir the oxidation state, demonstrate potential for p-type conduction if the Fermi level (μF) falls in the range of 0-0.8 eV from the valence band maximum (VBM) and the Ir concentration is high enough (12.5% in the present DFT calculations). Even though the corresponding calculated Seebeck coefficient (S) around 80-89 μV K−1slightly exceeds the experimental values, we emphasise the presence of an important plateau in the dependence ofSonμFin this range for two complexes with the formation of peroxide ions (O22−). We predicted also that peroxide ions O22−are characterized by the calculated phonon frequencies of 810-942 cm−1in agreement with our previous Raman experimental results. In this light, we discuss the high sensitivity of calculatedS(μF) dependences to the atomic and electronic structure.
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- Purans, J., et al.
(författare)
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Local electronic structure rearrangements and strong anharmonicity in YH3 under pressures up to 180 GPa
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The discovery of superconductivity above 250 K at high pressure in LaH10 and the prediction of overcoming the room temperature threshold for superconductivity in YH10 urge for a better understanding of hydrogen interaction mechanisms with the heavy atom sublattice in metal hydrides under high pressure at the atomic scale. Here we use locally sensitive X-ray absorption fine structure spectroscopy (XAFS) to get insight into the nature of phase transitions and the rearrangements of local electronic and crystal structure in archetypal metal hydride YH3 under pressure up to 180 GPa. The combination of the experimental methods allowed us to implement a multiscale length study of YH3: XAFS (short-range), Raman scattering (medium-range) and XRD (long-range). XANES data evidence a strong effect of hydrogen on the density of 4d yttrium states that increases with pressure and EXAFS data evidence a strong anharmonicity, manifested as yttrium atom vibrations in a double-well potential.
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- Revin, L. S., et al.
(författare)
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Spectral characteristics of the double-folded slot antennas with cold-electron bolometers for the 220/240 GHz channels of the LSPE instrument
- 2021
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 11:22
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of the experimental and theoretical study of the resonant properties and noise of a single cell of a receiving system based on cold-electron bolometers (CEB) with a double-folded slot antenna and coplanar lines. The system was designed to receive signals at 220/240 GHz frequencies with a 5% bandwidth. In measurements, we used the samples of the double-folded slot antennas with slot lengths of 162 um and coplanar line lengths from 185 to 360 um. Measurements of the resonance properties of CEB located at 0.3 K cryostat plate were carried out using a generator based on a high-temperature YBCO Josephson junction located inside the same cryostat at 4 K plate. This arrangement made it possible to obtain smooth amplitude-frequency characteristics with a clearly defined peak of a 15–21 GHz bandwidth at different frequencies. Based on these results, 2-D array of double-folded slot antennas with CEBs as 220/240 GHz LSPE channel prototype was calculated.The absorption efficiency of the array has reached 81% and 77% for 220 and 240 GHz channels, respectively.
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- Gordeeva, A. V., et al.
(författare)
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Record electron self-cooling in cold-electron bolometers with a hybrid superconductor-ferromagnetic nanoabsorber and traps
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- The Cosmic Microwave Background (CMB) radiation is the only observable that allows studying the earliest stage of the Universe. Radioastronomy instruments for CMB investigation require low working temperatures around 100 mK to get the necessary sensitivity. On-chip electron cooling of receivers is a pathway for future space missions due to problems of dilution fridges at low gravity. Here, we demonstrate experimentally that in a Cold-Electron Bolometer (CEB) a theoretical limit of electron cooling down to 65 mK from phonon temperature of 300 mK can be reached. It is possible due to effective withdrawing of hot electrons from the tunnel barrier by double stock, special traps and suppression of Andreev Joule heating in hybrid Al/Fe normal nanoabsorber.
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- Pankratov, A. L., et al.
(författare)
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Towards a microwave single-photon counter for searching axions
- 2022
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- The major task of detecting axions or axion-like particles has two challenges. On the one hand, the ultimate sensitivity is required, down to the energy of a single microwave photon of the yoctojoule range. On the other hand, since the detected events are supposed to be rare, the dark count rate of the detector must be extremely low. We show that this trade-off can be approached due to the peculiar switching dynamics of an underdamped Josephson junction in the phase diffusion regime. The detection of a few photons' energy at 10 GHz with dark count time above 10 s and the efficiency close to unity was demonstrated. Further enhancements require a detailed investigation of the junction switching dynamics.
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- Revin, L. S., et al.
(författare)
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Microwave photon detection by an Al Josephson junction
- 2020
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Ingår i: Beilstein Journal of Nanotechnology. - : Beilstein Institut. - 2190-4286. ; 11, s. 960-965
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Tidskriftsartikel (refereegranskat)abstract
- An aluminium Josephson junction (JJ), with a critical current suppressed by a factor of three compared with the maximal value calculated from the gap, is experimentally investigated for application as a threshold detector for microwave photons. We present the preliminary results of measurements of the lifetime of the superconducting state and the probability of switching by a 9 GHz external signal. We found an anomalously large lifetime, not described by the Kramers' theory for the escape time over a barrier under the influence of fluctuations. We explain it by the phase diffusion regime, which is evident from the temperature dependence of the switching current histograms. Therefore, phase diffusion allows for a significant improvement of the noise immunity of a device, radically decreasing the dark count rate, but it will also decrease the single-photon sensitivity of the considered threshold detector. Quantization of the switching probability tilt as a function of the signal attenuation for various bias currents through the JJ is observed, which resembles the differentiation between N and N + 1 photon absorption.
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| 9. |
- Revin, L. S., et al.
(författare)
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Response of a cold-electron bolometer on thz radiation from a long yba 2 cu 3 o 7−δ bicrystal josephson junction
- 2020
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 10:21, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The response of the Cold-Electron Bolometers (CEBs), integrated into a 2-D array of dipole antennas, has been measured by irradiation from YBa2Cu3O7−δ (YBCO) 50 µm long Josephson junction into the THz region at frequencies from 0.1 to 0.8 THz. The possibility of controlling the amplitude-frequency characteristic is demonstrated by the external magnetic field in the traveling wave regime of a long Josephson junction. The YBCO junction has been formed on the bicrystal Zr1−xYxO2 (YSZ) substrate by magnetron sputtering and etching of the film. CEBs have been fabricated using an Al multilayer structure by a self-aligned shadow evaporation technique on Si substrate. Both receiver and oscillator have been located inside the same cryostat at 0.3 K and 2.7 K plates, respectively.
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| 10. |
- Yablokov, Anton A., et al.
(författare)
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Resonant response drives sensitivity of Josephson escape detector
- 2021
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Ingår i: Chaos, Solitons and Fractals. - : Elsevier BV. - 0960-0779. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- The Josephson junction as a switching detector of weak signals is investigated in presence of noise in the frame of rotating pendulum model. The parameter range, where the detection can be more efficient, is found. It has been demonstrated, that with decrease of the signal power the double minima of the mean switching time and the standard deviation are transformed into a single minimum, which corresponds to interplay between noise suppression and resonant activation regimes. The resonant nature of escape allows to detect weak signals, whose amplitudes are weaker than the difference between critical current and bias current of a Josephson junction. With decrease of damping an efficient detection becomes possible even at subharmonics of the resonance frequency.
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