12 research outputs found
Interplay of the Inverse Proximity Effect and Magnetic Field in Out-of-Equilibrium Single-Electron Devices
We show that a weak external magnetic field affects significantly nonequilibrium quasiparticle (QP) distributions under the conditions of the inverse proximity effect, using the single-electron hybrid turnstile as a generic example. Inverse proximity suppresses the superconducting gap in superconducting leads in the vicinity of turnstile junctions, thus, trapping hot QPs in this region. An external magnetic field creates additional QP traps in the leads in the form of vortices or regions with a reduced superconducting gap resulting in the release of QPs away from the junctions. We present clear experimental evidence of the interplay of the inverse proximity effect and magnetic field revealing itself in the superconducting gap enhancement and significant improvement of the turnstile characteristics. The observed interplay and its theoretical explanation in the context of QP overheating are important for various superconducting and hybrid nanoelectronic devices, which find applications in quantum computation, photon detection, and quantum metrology
Spectrum of Andreev bound states in Josepshon junctions with a ferromagnetic insulator
Ferromagnetic-insulator (FI) based Josephson junctions are promising
candidates for a coherent superconducting quantum bit as well as a classical
superconducting logic circuit. Recently the appearance of an intriguing
atomic-scale 0-pi transition has been theoretically predicted. In order to
uncover the mechanism of this phenomena, we numerically calculate the spectrum
of Andreev bound states in a FI barrier by diagonalizing the Bogoliubov-de
Gennes equation. We show that Andreev spectrum drastically depends on the
parity of the FI-layer number L and accordingly the pi (0) state is always more
stable than the 0 (pi) state if L is odd (even).Comment: 6 pages, 5 figures, Invited Report on the Moscow International
Symposium on Magnetism MISM201
Joule heating effects in high-Transparency Josephson junctions
| openaire: EC/H2020/670743/EU//QuDeTWe study, both theoretically and experimentally, the features on the current-voltage characteristic of a highly transparent Josephson junction caused by transition of the superconducting leads to the normal state. These features appear due to the suppression of the Andreev excess current. We show that by tracing the dependence of the voltage, at which the transition occurs, on the bath temperature and by analyzing the suppression of the excess current by the bias voltage one can recover the temperature dependence of the heat flow out of the junction. We verify theory predictions by fabricating two highly transparent superconductor-graphene-superconductor (SGS) Josephson junctions with suspended and nonsuspended graphene as a nonsuperconducting section between Al leads. Applying the above mentioned technique we show that the cooling power of the suspended junction depends on the bath temperature as â Tbath3.1 close to the superconducting critical temperature.Peer reviewe
Superconducting Diode Effect in Topological Hybrid Structures
Currently, the superconducting diode effect (SDE) is being actively discussed, due to its large application potential in superconducting electronics. In particular, superconducting hybrid structures, based on three-dimensional (3D) topological insulators, are among the best candidates, due to their having the strongest spin–orbit coupling (SOC). Most theoretical studies on the SDE focus either on a full numerical calculation, which is often rather complicated, or on the phenomenological approach. In the present paper, we compare the linearized and nonlinear microscopic approaches in the superconductor/ferromagnet/3D topological insulator (S/F/TI) hybrid structure. Employing the quasiclassical Green’s function formalism we solve the problem self-consistently. We show that the results obtained by the linearized approximation are not qualitatively different from the nonlinear solution. The main distinction in the results between the two methods was quantitative, i.e., they yielded different supercurrent amplitudes. However, when calculating the so-called diode quality factor the quantitative difference is eliminated and both approaches result in good agreement
Site-specific photolabile roadblocks for the study of transcription elongation in biologically complex systems
Transcriptional pausing is crucial for the timely expression of genetic information. Biochemical methods quantify the half-life of paused RNA polymerase (RNAP) by monitoring restarting complexes across time. However, this approach may produce apparent half-lives that are longer than true pause escape rates in biological contexts where multiple consecutive pause sites are present. We show here that the 6-nitropiperonyloxymethyl (NPOM) photolabile group provides an approach to monitor transcriptional pausing in biological systems containing multiple pause sites. We validate our approach using the well-studied his pause and show that an upstream RNA sequence modulates the pause half-life. NPOM was also used to study a transcriptional region within the Escherichia coli thiC riboswitch containing multiple consecutive pause sites. We find that an RNA hairpin structure located upstream to the region affects the half-life of the 5′ most proximal pause site—but not of the 3′ pause site—in contrast to results obtained using conventional approaches not preventing asynchronous transcription. Our results show that NPOM is a powerful tool to study transcription elongation dynamics within biologically complex systems
Structural Disorder in Higher-Temperature Phases Increases Charge Carrier Lifetimes in Metal Halide Perovskites
Solar cells and optoelectronic devices are exposed to heat that degrades performance. Therefore,
elucidating temperature-dependent charge carrier dynamics is essential
for device optimization. Charge carrier lifetimes decrease with temperature
in conventional semiconductors. The opposite, anomalous trend is observed
in some experiments performed with MAPbI3 (MA = CH3NH3+) and other metal halide perovskites.
Using ab initio quantum dynamics simulation, we establish the atomic
mechanisms responsible for nonradiative electron–hole recombination
in orthorhombic-, tetragonal-, and cubic MAPbI3. We demonstrate
that structural disorder arising from the phase transitions is as
important as the disorder due to heating in the same phase. The carrier
lifetimes grow both with increasing temperature in the same phase
and upon transition to the higher-temperature phases. The increased
lifetime is rationalized by structural disorder that induces partial
charge localization, decreases nonadiabatic coupling, and shortens
quantum coherence. Inelastic and elastic electron–vibrational
interactions exhibit opposite dependence on temperature and phase.
The partial disorder and localization arise from thermal motions of
both the inorganic lattice and the organic cations and depend significantly
on the phase. The structural deformations induced by thermal fluctuations
and phase transitions are on the same order as deformations induced
by defects, and hence, thermal disorder plays a very important role.
Since charge localization increases carrier lifetimes but inhibits
transport, an optimal regime maximizing carrier diffusion can be designed,
depending on phase, temperature, material morphology, and device architecture.
The atomistic mechanisms responsible for the enhanced carrier lifetimes
at elevated temperatures provide guidelines for the design of improved
solar energy and optoelectronic materials