We report an experimental study of proximity induced superconductivity in planar Josephson junction devices made from free-standing InAs nanosheets. The nanosheets are grown by molecular beam ...epitaxy, and the Josephson junction devices are fabricated by directly contacting the nanosheets with superconductor Al electrodes. The fabricated devices are explored by low-temperature carrier transport measurements. The measurements show that the devices exhibit a gate-tunable supercurrent, multiple Andreev reflections, and a good quality superconductor-semiconductor interface. The superconducting characteristics of the Josephson junctions are investigated at different magnetic fields and temperatures and are analyzed based on the Bardeen–Cooper–Schrieffer (BCS) theory. The measurements of the ac Josephson effect are also conducted under microwave radiations with different radiation powers and frequencies, and integer Shapiro steps are observed. Our work demonstrates that InAs nanosheet based hybrid devices are desired systems for investigating the forefront of physics, such as two-dimensional topological superconductivity.
Semiconductor/superconductor hybrids exhibit a range of phenomena that can be exploited for the study of novel physics and the development of new technologies. Understanding the origin of the energy ...spectrum of such hybrids is therefore a crucial goal. Here, we study Josephson junctions defined by shadow epitaxy on InAsSb/Al nanowires. The devices exhibit gate-tunable supercurrents at low temperatures and multiple Andreev reflections (MARs) at finite voltage bias. Under microwave irradiation, photon-assisted tunneling (PAT) of MARs produces characteristic oscillating sidebands at quantized energies, which depend on MAR order, n, in agreement with a recently suggested modification of the classical Tien–Gordon equation. The scaling of the quantized energy spacings with microwave frequency provides independent confirmation of the effective charge, ne, transferred by the nth-order tunneling process. The measurements suggest PAT as a powerful method for assigning the origin of low-energy spectral features in hybrid Josephson devices.
Interfaces between materials with different electronic ground states have become powerful platforms for creating and controlling novel quantum states of matter, in which inversion symmetry breaking ...and other effects at the interface may introduce additional electronic states. Among the emergent phenomena, superconductivity is of particular interest. Here, by depositing metal films on a newly identified topological semimetal tungsten carbide (WC) single crystal, interfacial superconductivity is obtained, evidenced from soft point‐contact spectroscopy. This very robust phenomenon is demonstrated for a wide range of metal/WC interfaces, involving both nonmagnetic and ferromagnetic films, and the superconducting transition temperatures are surprisingly insensitive to the magnetism of thin films. This method offers an opportunity to explore the long‐sought topological superconductivity and has potential applications in topological‐state‐based spin devices.
Interfacial superconductivity is realized in topological semimetal tungsten carbide (WC)/normal‐metal heterostructures. The induced superconductivity is found to be insensitive to the magnetism, which is very different from the case of conventional superconductors, most probably indicating an unconventional nature of the pairing mechanism. The results provide a new direction for exploring topological superconductivity and designing novel topological quantum devices.
We have realized an integer quantum Hall system with superconducting contacts by connecting graphene to niobium electrodes. Below their upper critical field of 4 T, an integer quantum Hall effect ...coexists with superconductivity in the leads but with a plateau conductance that is larger than in the normal state. We ascribe this enhanced quantum Hall plateau conductance to Andreev processes at the graphene–superconductor interface leading to the formation of so-called Andreev edge-states. The enhancement depends strongly on the filling-factor and is less pronounced on the first plateau due to the special nature of the zero energy Landau level in monolayer graphene.
Superconducting proximity junctions made of topological insulator (TI) nanoribbons (NRs) provide a useful platform for studying topological superconductivity. We report on the fabrication and ...measurement of Josephson junctions (JJs) using Sb-doped Bi2Se3 NRs in contact with Al electrodes. Aharonov–Bohm and Altshuler–Aronov–Spivak oscillations of the axial magneto-conductance of TI NR were observed, indicating the existence of metallic surface states along the circumference of the TI NR. We observed the supercurrent in the TI NR JJ and subharmonic gap structures of the differential conductance due to multiple Andreev reflections. The interface transparency of the TI NR JJs estimated based on the excess current reaches τ = 0.83, which is among the highest values reported for TI JJs. The temperature dependence of critical current is consistent with the short and ballistic junction model confirming the formation of highly transparent superconducting contacts on the TI NR. Our observations would be useful for exploring topological Josephson effects in TI NRs.
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•Superconducting-proximity junctions were made of Sb-doped Bi2Se3 topological insulator (TI) nanoribbon (NR).•Our TI NR exhibited h/e- and h/2e-periodic magnetoconductance oscillations with the axial magnetic field.•We observed the subharmonic gap structures of the differential conductance due to the multiple Andreev reflections.•The interface transparency was estimated to be 0.83, which is among the highest values reported so far.
In this paper, we study the quantum transport properties in a double-quantum-dot circuit with two laterally-coupled superconductors. It is clearly found that with the adjustment of the phase ...difference between the superconductors, the electron tunneling and the local and crossed Andreev reflections display different characteristics. This phenomenon can be observed in the linear and nonlinear regimes, even in the presence of Coulomb interaction terms. Moreover, appropriate superconducting phase differences can efficiently enhance the crossed Andreev reflection, accompanied by the suppression of the local Andreev reflection and electron tunneling processes. Therefore, this setup can be used to be a promising device to realize the Cooper-pair splitting.
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