In this study, the realization of mesoscopic Josephson junctions based on free‐standing InSb nanosheet grown by molecular‐beam epitaxy is reported. Below the critical temperature of superconducting ...aluminium electrodes (≈1.1 K), the high transparency of the contacts gives rise to proximity‐induced superconductivity. A dissipationless supercurrent which can be modulated by a gate voltage acting on the electron density in the nanosheet flows through the superconducting weak links. At finite bias voltage, subharmonic energy‐gap structures (SGS) originating from multiple Andreev reflections (MARs) are observed, indicating a highly transparent InSb nanosheet–superconductor interface. At last, a superconducting hybrid device with niobium electrodes is shown, suitable for further higher temperature and magnetic field transport measurements.
This study reports the realization of mesoscopic Josephson junctions based on InSb nanosheet. Below the critical temperature of superconducting aluminium electrodes, a dissipationless supercurrent flows through the superconducting weak links. It can be modulated by a gate voltage. At finite bias voltage, subharmonic energy‐gap structures originating from multiple Andreev reflections are observed. At last, a superconducting hybrid device with niobium electrodes is shown for further measurements.
Herein, a new mechanism of steady‐state light amplification without inversion from a hybrid quantum dot circuit coupled to a single mode of electromagnetic resonator is theoretically investigated. ...Hybrid quantum dot circuit consists of a single‐level quantum dot which is connected weakly to one normal metal electrode and strongly to one superconducting electrode. Using the Floquet nonequilibrium Green's function technique, it is shown that the gain originates from the Andreev reflection processes at proper gate voltages when the bias voltage exceeds a certain threshold. Also, it is found that the inversionless light amplification is mediated by spin transitions between Andreev and Floquet–Andreev bound states in the superconducting energy gap.
Herein, a new mechanism of steady‐state light amplification without inversion from a hybrid quantum dot circuit coupled to a resonator is theoretically investigated. It is shown that the gain originates from the Andreev reflection processes and found that the inversionless light amplification is mediated by spin transitions between Andreev and Floquet–Andreev bound states in the superconducting energy gap.
We performed comprehensive studies of nearly optimal fluorine-substituted GdO1−xFx FeAs oxypnictide superconductors with TC=48−53K. Specific heat measurements revealed a sharp peak at T=3.5K that ...shifts to lower temperatures with magnetic field increase. This peak corresponds to an antiferromagnetic ordering in Gd3+ ion sublattice and may indicate coexistence between superconducting and magnetic orderings. Andreev transport through artificially made constriction demonstrated two channels for the carriers from the band(s) with the large superconducting gap as well as from those with the small gap. As expected, the presence of a transport channel with the bands mixing (ΔL+ΔS) was not detected. Using intrinsic multiple Andreev reflections effect (IMARE) spectroscopy, we determined two superconducting gaps, ΔS≈2.7meV, and ΔL≈11.6meV. The reproducible fine structure in the dI(V)/dV spectra of the Andreev contacts (satellites of the main subharmonic gap structure for ΔL) was interpreted as caused by a resonant emission of bosons with the energy ε0=12−15meV≈ΔL+ΔS during the process of multiple Andreev reflections (MAR) for normal carriers in ΔL-band(s) transport channel.
The structure of the superconducting order parameter of LiFeAs is studied by incoherent multiple Andreev reflections effect (IMARE) spectroscopy. The high transparent superconductor–thin normal ...metal–superconductor (SnS) contacts are created by a planar “break-junction” technique. Below
T
c
≈
17.5
K, the obtained I(V) and dI(V)/dV characteristics of SnS junctions show a presence of at least three bulk superconducting order parameters in LiFeAs. We directly determine the magnitudes, characteristic ratios, and temperature dependences of the superconducting gaps and discuss their symmetry.
Highlights
Three-gap superconductivity with possible momentum dependence (anisotropy) in LiFeAs.
Temperature dependences of the superconducting gaps indicate a moderate interband coupling.
Superconducting energy parameters scale with
T
c
under minor lithium deficiency.
We use the Landauer–Büttiker scattering theory for electronic transport to calculate the current cross-correlations in a voltage-biased three-terminal junction with all superconducting leads. At low ...bias voltage, when charge transport is due to coherent multiple Andreev reflections, we find large cross-correlations compared with their normal-state value. Furthermore, depending on the parameters that characterize the properties of the scattering region between the leads, the cross-correlations can reverse their sign with respect to the case of non-interacting fermionic systems.
•We study current correlations in voltage-biased 3-terminal Josephson junctions.•At low voltage, large and positive cross-correlations can be realized.•The interplay between supercurrents and quasiparticle transport is nontrivial.
Sandwich-type MgB2/Boron/MgB2 Josephson junctions were fabricated using magnetron sputtering system. The rapid-anneal process was adopted to replace traditional way of annealing, trying to solve the ...problem of interdiffusion and oxidation with multilayer films. The boron film was used as barrier layer to avoid the introduction of impurities and improve reproducibility of the junctions. The bottom MgB2 thin films deposited on c-plane sapphire substrate exhibits a critical temperature TC of 37.5 K and critical current density JC at 5 K of 8.7 × 106 A cm−2. From the XRD pattern, the bottom MgB2 thin film shows c-axis orientation, whereas the top MgB2 became polycrystalline as Boron barrier layer grown thicker. Therefore, all junction samples show lower TC than single MgB2 thin film. The junctions exhibit excellent quasiparticle characteristics with ideal dependence on temperature and Boron barrier thickness. Subharmonic gap structure was appeared in conductance characteristics, which was attributed to the multiple Andreev reflections (MAR). The result demonstrates great promise of this new fabrication technology for MgB2 Josephson junction fabrication.
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•Sandwich-type MgB2/Boron/MgB2 Josephson junctions were fabricated.•The junctions were annealed after deposition with the rapid-anneal process.•The highest critical current is 25.3 mA at 5 K and remains non-zero near 25 K.•Subharmonic gap features can be observed in the dI/dV – V curves.
We use the Landauer–Büttiker scattering theory for electronic transport to calculate the current cross-correlations in a voltage-biased three-terminal junction with all superconducting leads. At low ...bias voltage, when charge transport is due to coherent multiple Andreev reflections, we find large cross-correlations compared with their normal-state value. Furthermore, depending on the parameters that characterize the properties of the scattering region between the leads, the cross-correlations can reverse their sign with respect to the case of non-interacting fermionic systems.
•We study current correlations in voltage-biased 3-terminal Josephson junctions.•At low voltage, large and positive cross-correlations can be realized.•The interplay between supercurrents and quasiparticle transport is nontrivial.
In superconducting quantum point contacts, multiple Andreev reflection (MAR), which describes the coherent transport of
m
quasiparticles each carrying an electron charge with
m
≥
3
, sets in at ...voltage thresholds
e
V
=
2
Δ
/
m
. In single-electron transistors, Coulomb blockade, however, suppresses the current at low voltage. The required voltage for charge transport increases with the square of the effective charge
e
V
∝
m
e
2
. Thus, studying the charge transport in all-superconducting single-electron transistors (SSETs) sets these two phenomena into competition. In this article, we present the fabrication as well as a measurement scheme and transport data for a SSET with one junction in which the transmission and thereby the MAR contributions can be continuously tuned. All regimes from weak to strong coupling are addressed. We extend the Orthodox theory by incorporating MAR processes to describe the observed data qualitatively. We detect a new transport process the nature of which is unclear at present. Furthermore, we observe a renormalization of the charging energy when approaching the strong coupling regime.
We show that Majorana fermions associated with Majorana flat bands emerge as zero energy modes on the 110 edge of single layer or multilayer nodal superconductors with dx2−y2-wave pairing and Rashba ...spin–orbit coupling. Moreover, as long as the global inversion symmetry of the single layer or multilayer superconductor is broken, and in the presence of an in-plane magnetic field parallel to the 110 edge, the Majorana fermions together with usual fermionic Andreev bound states induce a triple-peak structure in tunnelling spectroscopy experiments. Importantly, we show that the zero bias conductance peak is induced by Majorana fermions. Therefore, tunnelling spectroscopy can be used to probe Majorana fermions in nodal dx2−y2-wave superconductors.
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