Electrical Discharge in a Cavitating Liquid under an Ultrasound Field.

A theoretical model for an electrical discharge in a cavitating liquid is developed and compared with experiments for the optimization of the water treatment device. The calculations based on solution of the Noltingk─Neppiras equation support the hypothesis that the electric field promotes the formation of vapor microchannels inside a liquid gap between the electrodes, where at a low gas pressure Paschen's conditions of rupture and abnormal glow discharge maintenance in those microchannels are fulfilled. Theoretical analysis of the cavitation processes and the discharge formation processes is in qualitative agreement with the experimental data obtained in this work in a water treatment device using a hydrodynamic emitter.

Density of states in the presence of spin-dependent scattering in SF bilayers: a numerical and analytical approach.

We present a quantitative study of the density of states (DOS) in SF bilayers (where S is a bulk superconductor and F is a ferromagnetic metal) in the diffusive limit. We solve the quasiclassical Usadel equations in the structure considering the presence of magnetic and spin-orbit scattering. For practical reasons, we propose the analytical solution for the density of states in SF bilayers in the case of a thin ferromagnet and low transparency of the SF interface.

Physical Vapor Deposition Features of Ultrathin Nanocrystals of Bi(TeSe).

Structural and electronic properties of ultrathin nanocrystals of chalcogenide Bi(Te Se) were studied. The nanocrystals were formed from the parent compound BiTeSe on as-grown and thermally oxidized Si(100) substrates using Ar-assisted physical vapor deposition, resulting in well-faceted single crystals several quintuple layers thick and a few hundreds nanometers large. The chemical composition and structure of the nanocrystals were analyzed by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, electron backscattering, and X-ray diffraction.

Revealing Josephson Vortex Dynamics in Proximity Junctions below Critical Current.

Made of a thin non-superconducting metal (N) sandwiched by two superconductors (S), SNS Josephson junctions enable novel quantum functionalities by mixing up the intrinsic electronic properties of N with the superconducting correlations induced from S by proximity. Electronic properties of these devices are governed by Andreev quasiparticles (Andreev, A. 1965, 20, 1490) which are absent in conventional SIS junctions whose insulating barrier (I) between the two S electrodes owns no electronic states.

Environment-induced overheating phenomena in Au-nanowire based Josephson junctions.

Unlike conventional planar Josephson junctions, nanowire-based devices have a bridge geometry with a peculiar coupling to environment that can favor non-equilibrium electronic phenomena. Here we measure the influence of the electron bath overheating on critical current of several bridge-like junctions built on a single Au-nanowire. Using the Usadel theory and applying the two-fluid description for the normal and superconducting components of the flowing currents, we reveal and explain the mutual influence of the neighbouring junctions on their characteristics through various processes of the electron gas overheating.

Reappearance of first Shapiro step in narrow topological Josephson junctions.

In Josephson junctions, a supercurrent across a nonsuperconducting weak link is carried by electron-hole bound states. Because of the helical spin texture of nondegenerate topological surface states, gapless bound states are established in junctions with topological weak link. These have a characteristic 4π-periodic current phase relation (CΦR) that leads to twice the conventional Shapiro step separation voltage in radio frequency-dependent measurements.

Ultrastrong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers.

The critical step for future quantum industry demands realization of efficient information exchange between different-platform hybrid systems that can harvest advantages of distinct platforms. The major restraining factor for the progress in certain hybrids is weak coupling strength between the elemental particles. In particular, this restriction impedes a promising field of hybrid magnonics.

Magnetic Gap of Fe-Doped BiSbTeSe Bulk Single Crystals Detected by Tunneling Spectroscopy and Gate-Controlled Transports.

Topological insulators with broken time-reversal symmetry and the Fermi level within the magnetic gap at the Dirac cone provides exotic topological magneto-electronic phenomena. Here, we introduce an improved magnetically doped topological insulator, Fe-doped BiSbTeSe (Fe-BSTS) bulk single crystal, with an ideal Fermi level. Scanning tunneling microscopy and spectroscopy (STM/STS) measurements revealed that the surface state possesses a Dirac cone with the Dirac point just below the Fermi level by 12 meV.

Disorder-Promoted Splitting in Quasiparticle Interference at Nesting Vectors.

Inelastic interactions of quantum systems with the environment usually wash coherent effects out. In the case of Friedel oscillations, the presence of disorder leads to a fast decay of the oscillation amplitude. Here we show both experimentally and theoretically that in three-dimensional topological insulator BiTe there is a nesting-induced splitting of coherent scattering vectors which follows a peculiar evolution in energy.

Electronic Structures and Surface Reconstructions in Magnetic Superconductor RbEuFeAs.

In pnictide RbEuFeAs, superconductivity sets in at 36 K and coexists, below 15-19 K, with the long-range magnetic ordering of Eu 4f spins. Here we report scanning tunneling experiments performed on cold-cleaved single crystals of the compound. The data revealed the coexistence of large Rb-terminated and small Eu-terminated terraces, both manifesting 1 × 2 and reconstructions.

Anomalous magneto-resistance of Ni-nanowire/Nb hybrid system.

We examine the influence of superconductivity on the magneto-transport properties of a ferromagnetic Ni nanowire connected to Nb electrodes. We show experimentally and confirm theoretically that the Nb/Ni interface plays an essential role in the electron transport through the device. Just below the superconducting transition, a strong inverse proximity effect from the nanowire suppresses superconducting correlations at Nb/Ni interfaces, resulting in a conventional anisotropic magneto-resistive response.

Author Correction: Local Josephson vortex generation and manipulation with a Magnetic Force Microscope.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Local Josephson vortex generation and manipulation with a Magnetic Force Microscope.

Josephson vortices play an essential role in superconducting quantum electronics devices. Often seen as purely conceptual topological objects, 2π-phase singularities, their observation and manipulation are challenging. Here we show that in Superconductor-Normal metal-Superconductor lateral junctions Josephson vortices have a peculiar magnetic fingerprint that we reveal in Magnetic Force Microscopy (MFM) experiments.

Ferromagnet/Superconductor Hybrid Magnonic Metamaterials.

In this work, a class of metamaterials is proposed on the basis of ferromagnet/superconductor hybridization for applications in magnonics. These metamaterials comprise of a ferromagnetic magnon medium that is coupled inductively to a superconducting periodic microstructure. Spectroscopy of magnetization dynamics in such hybrid evidences formation of areas in the medium with alternating dispersions for spin wave propagation, which is the basic requirement for the development of metamaterials known as magnonic crystals.

Selective area growth and stencil lithography for in situ fabricated quantum devices.

The interplay of Dirac physics and induced superconductivity at the interface of a 3D topological insulator (TI) with an s-wave superconductor (S) provides a new platform for topologically protected quantum computation based on elusive Majorana modes. To employ such S-TI hybrid devices in future topological quantum computation architectures, a process is required that allows for device fabrication under ultrahigh vacuum conditions. Here, we report on the selective area growth of (Bi,Sb)Te TI thin films and stencil lithography of superconductive Nb for a full in situ fabrication of S-TI hybrid devices via molecular-beam epitaxy.

4π-periodic Andreev bound states in a Dirac semimetal.

Although signatures of superconductivity in Dirac semimetals have been reported, for instance by applying pressure or using point contacts, our understanding of the topological aspects of Dirac semimetal superconductivity is still developing. Here, we utilize nanoscale phase-sensitive junction technology to induce superconductivity in the Dirac semimetal BiSb. Our radiofrequency irradiation experiments then reveal a significant contribution of 4π-periodic Andreev bound states to the supercurrent in Nb-BiSb-Nb Josephson junctions.

Probing pairing symmetry in multi-band superconductors by quasiparticle interference.

We study momentum and energy dependencies of the quasiparticle interference (QPI) response function in multiband superconductors in the framework of the strong-coupling Eliashberg approach. Within an effective two-band model we study the s and s symmetry cases, corresponding to opposite or equal signs of the order parameters in the bands. We demonstrate that the momentum dependence of the QPI function is strikingly different for s and s symmetries of the order parameter at energies close to the small gap.

Domain Meissner state and spontaneous vortex-antivortex generation in the ferromagnetic superconductor EuFe(AsP).

The interplay between superconductivity and magnetism is one of the oldest enigmas in physics. Usually, the strong exchange field of ferromagnet suppresses singlet superconductivity via the paramagnetic effect. In EuFe(AsP), a material that becomes not only superconducting at 24.

Expansion of a superconducting vortex core into a diffusive metal.

Vortices in quantum condensates exist owing to a macroscopic phase coherence. Here we show, both experimentally and theoretically, that a quantum vortex with a well-defined core can exist in a rather thick normal metal, proximized with a superconductor. Using scanning tunneling spectroscopy we reveal a proximity vortex lattice at the surface of 50 nm-thick Cu-layer deposited on Nb.

Odd-frequency superconductivity induced in topological insulators with and without hexagonal warping.

We study the effect of the Fermi surface anisotropy on the odd-frequency spin-triplet pairing component of the induced pair potential. We consider a superconductor/ ferromagnetic insulator (S/FI) hybrid structure formed on the 3D topological insulator (TI) surface. In this case three ingredients ensure the possibility of the odd-frequency pairing: (1) the topological surface states, (2) the induced pair potential, and (3) the magnetic moment of a nearby ferromagnetic insulator.

Andreev Reflection in an s-Type Superconductor Proximized 3D Topological Insulator.

We investigate transport and shot noise in lateral normal-metal-3D topological-insulator-superconductor contacts, where the 3D topological insulator (TI) is based on Bi. In the normal state, the devices are in the elastic diffusive transport regime, as demonstrated by a nearly universal value of the shot noise Fano factor F_{N}≈1/3 in magnetic field and in a reference normal-metal contact. In the absence of magnetic field, we identify the Andreev reflection (AR) regime, which gives rise to the effective charge doubling in shot noise measurements.

Critical behavior at a dynamic vortex insulator-to-metal transition.

An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables investigation of the nature of competing vortex states and phase transitions between them. A square array creates the eggcrate potential in which magnetic field-induced vortices are frozen into a vortex insulator.

Observability of surface Andreev bound states in a topological insulator in proximity to an s-wave superconductor.

To guide experimental work on the search for Majorana zero-energy modes, we calculate the superconducting pairing symmetry of a three-dimensional topological insulator in combination with an s-wave superconductor. We show how the pairing symmetry changes across different topological regimes. We demonstrate that a dominant p-wave pairing relation is not sufficient to realise a Majorana zero-energy mode useful for quantum computation.