Helical states can be measured through the observation of the reentrant behaviour, which is a dip in the conductance probed in semiconducting nanowires (NWs) with strong spin-orbit coupling (SOC) under the presence of an external perpendicular magnetic field. We investigate the effects of deformations in the electronic transport in NWs considering the coupling between different transverse modes. Within this approach, we show that the dip in the conductance of a NW is affected by the presence of a local constriction. Moreover, we find that the reentrant feature in the conductance can appear in NWs with a local expansion of its radius, even in the absence of SOC and magnetic field. Furthermore, we develop a numerical approach to calculate transport properties, which is able to include the deformation and the coupling among several scattering channels.
The demonstration of strong photoluminescence polarization anisotropy in semiconducting nanowires embodies both technological promise and scientific challenge. Here we present progress on both fronts through the study of the photoluminescence polarization anisotropy of randomly oriented nanowire ensembles in materials without/with crystalline anisotropy, small/wide bandgap, and both III-V/II-VI chemistry (InP/ZnO nanowires, respectively). Comprehensive control of the polarization anisotropy is realized by dielectric matching with conformally deposited Ta2O5 (dielectric ratios of 9.6:4.41 and 4…
We have probed the superconducting proximity effect through long high-quality monocrystalline Ag nanowires, by realizing Josephson junctions of different lengths, with different superconducting materials. Thanks to the high number of junctions probed, both the contact resistance and electron diffusion constant could be determined, enabling a comparison of the measured critical current to theoretical expectation, over the entire regime from short to long diffusive junction. Although the length dependence of the critical current is as expected, the amplitude of the $R_{N}I_c$ product is smaller …
We propose a new orbital controlled model to explain the gate field induced switching of current in a semiconducting PbS-nanowire junction. A single particle scattering formalism in conjunction with a posteriori density functional approach involving hybrid functional is used to study the electronic current; both first and higher order Stark effects are explicitly treated in our model. Our calculation reveals that after a threshold gate-voltage, orbital mixing produces p-components at the S atoms in the participating orbitals. This results in an inter-layer orbital interaction that allows elect…
We investigate the effect of electron-electron interactions on proximity-induced $s$-wave superconductivity in one-dimensional nanowires. We treat the interactions on a self-consistent mean-field level, and find an analytic expression for the effective pairing potential in the presence of interactions, valid for a weakly tunnel coupled wire. We show that for a set of two nanowires placed in parallel on a superconducting substrate, the interaction-induced reduction of the pairing energy could result in the effective interwire pairing potential exceeding the intrawire potential, which is one of …
We study both analytically and numerically the role of orbital effects caused by a magnetic field applied along the axis of a semiconducting Rashba nanowire in the topological regime hosting Majorana fermions. We demonstrate that the orbital effects can be effectively taken into account in a one-dimensional model by shifting the chemical potential, and, thus modifying the topological criterion. We focus on the energy splitting between two Majorana fermions in a finite nanowire and find a striking interplay between orbital and Zeeman effects on this splitting. In the limit of strong spin-orbit …
Semiconducting-superconducting nanowires attract widespread interest owing to the possible presence of non-abelian Majorana zero modes, which hold promise for topological quantum computation. However, the search for Majorana signatures is challenging because reproducible hybrid devices with desired nanowire lengths and material parameters need to be reliably fabricated to perform systematic explorations in gate voltages and magnetic fields. Here, we exploit a fabrication platform based on shadow walls that enables the in-situ, selective and consecutive depositions of superconductors and normal…
The dielectric environment of thin semiconductor nanowires can affect the charge transport properties inside the wire. In this work, it is shown that Coulomb impurity scattering inside thin nanowires can be damped strongly by coating the wire with a high-k dielectric. This will lead to an increase in the mobility of free charges inside the wire.
We study Josephson junctions made of semiconducting nanowires with Rashba spin-orbit coupling, where superconducting correlations are induced by the proximity effect. In the presence of a suitably directed magnetic field, the system displays the anomalous Josephson effect: a nonzero supercurrent in the absence of a phase bias between two superconductors. We show that this anomalous current can be increased significantly by tuning the nanowire into the helical regime. In particular, in a short junction, a large anomalous current is a signature for topologically nontrivial superconductivity in t…
Many thermoelectrics like Bi exhibit Rashba spin-orbit surface bands for which topological insulator behavior consisting of ultrahigh mobilities and enhanced thermopower has been predicted. Bi nanowires realize surface-only electronic transport since they become bulk insulators when they undergo the bulk semimetal-semiconductor transition as a result of quantum confinement for diameters close to 50 nm. We studied 20-, 30-, 50- and 200-nm trigonal Bi wires. Shubnikov-de Haas magnetoresistance oscillations caused by surface electrons and bulklike holes enable the determination of their densities…
Following significant progress in the visualization and characterization of Majorana end modes in hybrid systems of semiconducting nanowires and superconducting islands, much attention is devoted to the investigation of the electronic structure at the buried interface between the semiconductor and the superconductor. The properties of that interface and the structure of the electronic wavefunctions that occupy it determine the functionality and the topological nature of the superconducting state induced therein. Here we study this buried interface by performing spectroscopic mappings of superc…
Spin-momentum locking in a semiconductor device with strong spin-orbit coupling (SOC) is a fundamental goal of nanoscale spintronics and an important prerequisite for the formation of Majorana bound states. Such a helical state is predicted in one-dimensional (1D) nanowires subject to strong Rashba SOC and spin-mixing, its hallmark being a characteristic reentrant behaviour in the conductance. Here, we report the first direct experimental observations of the reentrant conductance feature, which reveals the formation of a helical liquid, in the lowest 1D subband of an InAs nanowire. Surprisingl…
The recent proposals of devices with overlapping Andreev bound states (ABS) open up the opportunities to control and fine-tune their spectrum, that can be used in various applications. In this Article, we study the ABS in a device consisting of a semiconducting nanowire covered with three superconducting leads. The ABS are formed at two junctions where the wire is not covered. They overlap in the wire where the electron propagation is 1D, and in one of the leads where the propagation is 3D. We identify a number of regimes where these two overlaps either dominate or compete, depending on the ju…
We report on a theoretical study of quantum charge transport in atomistic models of silicon nanowires with surface roughness-based disorder. Depending on the nanowires features (length, roughness profile) various conduction regimes are explored numerically by using efficient real space order N computational approaches of both Kubo-Greenwood and Landauer-Buttiker transport frameworks. Quantitative estimations of the elastic mean free paths, charge mobilities and localization lengths are performed as a function of the correlation length of the surface roughness disorder. The obtained values for …
We investigate transmon qubits made from semiconductor nanowires with a fully surrounding superconducting shell. In the regime of reentrant superconductivity associated with the destructive Little-Parks effect, numerous coherent transitions are observed in the first reentrant lobe, where the shell carries 2π winding of superconducting phase, and are absent in the zeroth lobe. As junction density was increased by gate voltage, qubit coherence was suppressed then lost in the first lobe. These observations and numerical simulations highlight the role of winding-induced Andreev states in the junct…
One of the most promising platforms for one-dimensional topological superconductivity is based on semiconducting nanowires with strong spin-orbit coupling (SOC), where s-wave superconductivity is induced by proximity effect and an external Zeeman field drives the system into the topological superconducting phase with Majorana bound states (MBSs) at the end of the wire. During last years this idea has led to a great number of important experiments in hybrid superconductor-semiconductor systems, where the main signature is an emergent zero-bias peak (ZBP) in the differential conductance as the Z…
The tunneling of quasiparticles (QPs) across Josephson junctions (JJs) detrimentally affects the coherence of superconducting and charge-parity qubits, and is shown to occur more frequently in magnetic fields. Here we demonstrate the parity lifetime to survive in excess of 50$\,\mathrmμ$s in magnetic fields up to 1$\,$T, utilising a semiconducting nanowire transmon to detect QP tunneling in real time. We exploit gate-tunable QP filters and find magnetic-field-enhanced parity lifetimes, consistent with increased QP trapping by the ungated nanowire due to orbital effects. Our findings highlight …
This review focuses on the investigation and enhancement of the thermoelectric properties of semiconducting nanowires (NWs). NWs are nanostructures with typical diameters between few to hundreds of nm and length of few to several microns, exhibiting a high surface-to-volume ratio. Nowadays an extraordinary control over their growth has been achieved, enabling also the integration of different types of heterostructures, which can lead to the engineering of the functional properties of the NWs. In this review, we discuss all concepts which have been presented and achieved so far for the improvem…
In this paper we present a detailed analysis of the atomic and electronic structure of GaAs nanowires using first-principles pseudopotential calculations. We consider six different types of nanowires with different diameters all grown along [111] direction and reveal interesting trends between cohesive energy and nanowire type with varying diameters. Generally, the average cohesive energy of nanowires with wurtzite stacking is higher than those with zinc blende stacking for small diameters. We found that most of the bare nanowires considered here are semiconducting and continue to be semicondu…
We report the realization of quantum microwave circuits using hybrid superconductor-semiconductor Josephson elements comprised of InAs nanowires contacted by NbTiN. Capacitively-shunted single elements behave as transmon qubits with electrically tunable transition frequencies. Two-element circuits also exhibit transmon-like behavior near zero applied flux, but behave as flux qubits at half the flux quantum, where non-sinusoidal current-phase relations in the elements produce a double-well Josephson potential. These hybrid Josephson elements are promising for applications requiring microwave su…
The modern understanding of the Josephson effect in mesosopic devices derives from the physics of Andreev bound states, fermionic modes that are localized in a superconducting weak link. Recently, Josephson junctions constructed using semiconducting nanowires have led to the realization of superconducting qubits with gate-tunable Josephson energies. We have used a microwave circuit QED architecture to detect Andreev bound states in such a gate-tunable junction based on an aluminum-proximitized InAs nanowire. We demonstrate coherent manipulation of these bound states, and track the bound-state …
The short coherence lengths characteristic of low-dimensional superconductors are associated with usefully high critical fields or temperatures. Unfortunately, such materials are often sensitive to disorder and suffer from phase fluctuations in the superconducting order parameter which diverge with temperature $T$, magnetic field $H$ or current $I$. We propose an approach to overcome synthesis and fluctuation problems: building superconductors from inhomogeneous composites of nanofilaments. Macroscopic crystals of quasi-one-dimensional Na$_{2-δ}$Mo$_6$Se$_6$ featuring Na vacancy disorder ($δ\a…
The novel idea that spin-orbit coupling (SOC) and $s$-wave pairing can lead to induced $p$-wave pairing at strong magnetic limit has stimulated widespread interests in the whole community for the searching of Majorana Fermions (MFs), a self-hermitian particle, in semiconductor-superconductor hybrid structures. However, this system has several inherent limitations that prohibit the realization and identification of MFs with the major advances of semiconductor nanotechnology. We show that these limitations can be resolved by replacing the $s$-wave superconductor with type-II Fulde-Ferrell (FF) s…
We propose a scheme in semiconducting quantum nanowires structure to demonstrate the non-Abelian statistics for Majorana fermions in terms of braid group. The Majorana fermions are localized at the endpoints of semiconducting wires, which are deposited on an \emph{s}-wave superconductor. The non-Abelian nature of Majorana fermion is manifested by the fact that the output of the different applied orders of two operations, constructed by the braid group elements, are different. In particular, the difference can be unambiguously imprinted on the quantum states of a superconducting flux qubit.
We show that Majorana edge modes appear in a strongly correlated phase of semiconducting nanowires with discrete rotational symmetry in the cross section. These modes exist in the absence of spin-orbit coupling, magnetic fields and superconductivity. They appear purely due to the combination of the three-dimensional Coulomb interaction and orbital physics, which generates a fermionic condensate exhibiting a topological ground state degeneracy in a sector of the spectrum which is gapped to continuum modes. The gap can be comparable in magnitude to the topological superconducting gap in other so…
Majorana Zero Modes (MZMs) are prime candidates for robust topological quantum bits, holding a great promise for quantum computing. Semiconducting nanowires with strong spin orbit coupling offers a promising platform to harness one-dimensional electron transport for Majorana physics. Demonstrating the topological nature of MZMs relies on braiding, accomplished by moving MZMs around each other in a certain sequence. Most of the proposed Majorana braiding circuits require nanowire networks with minimal disorder. Here, the electronic transport across a junction between two merged InSb nanowires i…
By utilizing the effective-field theory based on the Glauber-type stochastic dynamics, the dynamic behaviors of the hexagonal Ising nanowire (HIN) system in the presence of a time dependent magnetic field are obtained. The time variations of average order parameters and the thermal behavior of the dynamic order parameters are studied to analyze the nature of transitions and to obtain the dynamic phase transition points. The dynamic phase diagrams are introduced in the plane of the reduced temperature versus magnetic field amplitude. The dynamic phase diagrams exhibit coexistence phase region, …
We show that the boundary charge and spin can be used as alternative signatures of the topological phase transition in topological models such as semiconducting nanowires with strong Rashba spin-orbit interaction in the presence of a magnetic field and in proximity to an $s$-wave superconductor. We identify signatures of the topological phase transition that do not rely on the presence of Majorana zero-energy modes and, thus, can serve as independent probes of topological properties. The boundary spin component along the magnetic field, obtained by summing contributions from all states below t…
We study theoretically transport through a semiconducting nanowire (NW) in the presence of Rashba spin orbit interaction, uniform magnetic field, and spatially modulated magnetic field. The system is fully gapped, and the interplay between the spin orbit interaction and the magnetic fields leads to fractionally charged fermion (FF) bound states of Jackiw-Rebbi type at each end of the nanowire. We investigate the transport and noise behavior of a N/NW/N system, where the wire is contacted by two normal leads (N), and we look for possible signatures that could help in the experimental detection …
We consider time-reversal-symmetric two-channel semiconducting quantum wires proximity coupled to an s-wave superconductor. We analyze the requirements for a nontrivial topological phase and find that necessary conditions are 1) the determinant of the pairing matrix in channel space must be negative, 2) inversion symmetry must be broken, and 3) the two channels must have different spin-orbit couplings. The first condition can be implemented in semiconducting nanowire systems where interactions suppress intra-channel pairing, while the inversion symmetry can be broken by tuning the chemical pot…
We study hybrid superconducting-semiconducting nanowires in the presence of Rashba spin-orbit interaction as well as helical magnetic fields. We show that the interplay between them leads to a competition of phases with two topological gaps closing and reopening, resulting in unexpected reentrance behavior. Besides the topological phase with localized Majorana fermions (MFs) we find new phases characterized by fractionally charged fermion (FF) bound states of Jackiw-Rebbi type. The system can be fully gapped by the magnetic fields alone, giving rise to FFs that transmute into MFs upon turning …
A semiconducting nanowire fully wrapped by a superconducting shell has been proposed as a platform for obtaining Majorana modes at small magnetic fields. In this study, we demonstrate that the appearance of subgap states in such structures is actually governed by the junction region in tunneling spectroscopy measurements, and not the full-shell nanowire itself. Short tunneling regions never show subgap states, whereas longer junctions always do. This can be understood in terms of quantum dots forming in the junction and hosting Andreev levels in the Yu-Shiba-Rusinov regime. The intricate magne…
We show a hard induced superconducting gap in a Ge-Si nanowire Josephson transistor up to in-plane magnetic fields of $250$ mT, an important step towards creating and detecting Majorana zero modes in this system. A hard induced gap requires a highly homogeneous tunneling heterointerface between the superconducting contacts and the semiconducting nanowire. This is realized by annealing devices at $180$ $^\circ$C during which aluminium inter-diffuses and replaces the germanium in a section of the nanowire. Next to Al, we find a superconductor with lower critical temperature ($T_\mathrm{C}=0.9$ K…
Finding ways of creating, measuring and manipulating Majorana bound states (MBSs) in superconducting-semiconducting nanowires is a highly pursued goal in condensed matter physics. It was recently proposed that a periodic covering of the semiconducting nanowire with superconductor fingers would allow both gating and tuning the system into a topological phase while leaving room for a local detection of the MBS wavefunction. We perform a detailed, self-consistent numerical study of a three-dimensional (3D) model for a finite-length nanowire with a superconductor superlattice including the effect …
We have investigated the stability and conductivity of unsupported, two dimensional infinite gold nanowires using ab-initio density functional theory (DFT). Two dimensional ribbon like nanowires, with 1-5 rows of gold atoms in the non-periodic direction and with different possible structures have been considered. The nanowires with > 2 rows of atoms exhibit dimerization, similar to finite wires, along the non-periodic direction. Our results show that in these zero thickness nanowires, the parallelogram motif is the most stable. A comparison between parallelogram and rectangular shaped nanowire…
Recent advances in the growth of III-V semiconductor nanowires (NWs) hold great promise for nanoscale optoelectronic device applications. Recently, it was found that a small amount of nitrogen (N) incorporation in III-V semiconductor NWs can effectively red-shift their wavelength of operation and tailor their electronic properties for specific applications. However, understanding the impact of N incorporation on non-equilibrium charge carrier dynamics and transport in semiconducting NWs is critical in achieving efficient semiconducting NW devices. In this work, ultrafast optical pump-terahertz…
We report on sub-gap transport measurements of an InAs nanowire coupled to niobium nitride leads at high magnetic fields. We observe a zero-bias anomaly (ZBA) in the differential conductance of the nanowire for certain ranges of magnetic field and chemical potential. The ZBA can oscillate in width with either magnetic field or chemical potential; it can even split and reform. We discuss how our results relate to recent predictions of hybridizing Majorana fermions in semiconducting nanowires, while considering more mundane explanations.
A superconductor-semiconducting nanowire-superconductor heterostructure in the presence of spin orbit coupling and magnetic field can support a supercurrent even in the absence of phase difference between the superconducting electrodes. We investigate this phenomenon, the anomalous Josephson effect, employing a model capable of describing many bands in the normal region. We discuss geometrical and symmetry conditions required to have finite anomalous supercurrent and in particular we show that this phenomenon is enhanced when the Fermi level is located close to a band opening in the normal reg…
The motion of an electron and its spin are generally not coupled. However in a one dimensional material with strong spin-orbit interaction (SOI) a helical state may emerge at finite magnetic fields, where electrons of opposite spin will have opposite momentum. The existence of this helical state has applications for spin filtering and Cooper pair splitter devices and is an essential ingredient for realizing topologically protected quantum computing using Majorana zero modes. Here we report electrical conductance measurements of a quantum point contact (QPC) formed in an indium antimonide nanow…
Multiply connected superconductors smaller than the coherence length show destructive superconductivity, characterized by reentrant quantum phase transitions driven by magnetic flux. We investigate the dependence of destructive superconductivity on flux, transverse magnetic field, temperature, and current in InAs nanowires with a surrounding epitaxial Al shell, finding excellent agreement with mean-field theory across multiple reentrant transitions. Near the crossover between destructive and nondestructive regimes, an anomalous metal phase is observed with temperature-independent resistance, c…
We report a method for making epitaxial superconducting contacts to semiconducting nanowires. The temperature and gate characteristics demonstrate barrier-free electrical contact, and the properties in the superconducting state are investigated at low temperature. Half-covering aluminum contacts are realized without the need of lithography and we demonstrate how to controllably insert high-band gap layers in the interface region. These developments are relevant to hybrid superconductor-nanowire devices that support Majorana zero energy states.
We report an experimental study of one-dimensional (1D) electronic transport in an InSb semiconducting nanowire. Three bottom gates are used to locally deplete the nanowire creating a ballistic quantum point contact with only a few conducting channels. In a magnetic field, the Zeeman splitting of the corresponding 1D subbands is revealed by the emergence of conductance plateaus at multiples of $e^2$/h, yet we find a quantized conductance pattern largely dependent on the configuration of voltages applied to the bottom gates. In particular, we can make the first plateau disappear leaving a first…
We study theoretically the spin-orbit interaction of low-energy electrons in semiconducting nanowires with a zinc-blende lattice. The effective Dresselhaus term is derived for various growth directions, including <11(-2)>-oriented nanowires. While a specific configuration exists where the Dresselhaus spin-orbit coupling is suppressed even at confinement potentials of low symmetry, many configurations allow for a strong Dresselhaus coupling. In particular, we discuss qualitative and quantitative results for nanowire cross-sections modeled after sectors of rings or circles. The parameter depende…
A semiconductor transmon with an epitaxial Al shell fully surrounding an InAs nanowire core is investigated in the low $E_J/E_C$ regime. Little-Parks oscillations as a function of flux along the hybrid wire axis are destructive, creating lobes of reentrant superconductivity separated by a metallic state at a half-quantum of applied flux. In the first lobe, phase winding around the shell can induce topological superconductivity in the core. Coherent qubit operation is observed in both the zeroth and first lobes. Splitting of parity bands by coherent single-electron coupling across the junction …
Compound semiconducting nanowires are promising building blocks for several nanoelectronic devices yet the inability to reliably control their growth morphology is a major challenge. Here, we report the Au-catalyzed vapor-liquid-solid (VLS) growth of GaN nanowires with controlled growth direction, surface polarity and surface roughness. We develop a theoretical model that relates the growth form to the kinetic frustration induced by variations in the V(N)/III(Ga) ratio across the growing nanowire front. The model predictions are validated by the trends in the as-grown morphologies induced by s…
Semiconducting nanowires (NWs) are a versatile, highly tunable material platform at the heart of many new developments in nanoscale and quantum physics. Here, we demonstrate charge pumping, i.e., the controlled transport of individual electrons through an InAs NW quantum dot (QD) device at frequencies up to $1.3\,$GHz. The QD is induced electrostatically in the NW by a series of local bottom gates in a state of the art device geometry. A periodic modulation of a single gate is enough to obtain a dc current proportional to the frequency of the modulation. The dc bias, the modulation amplitude a…
Density functional theory and molecular dynamics simulations have been used to optimize the structure of nanowires of SiO2. The starting structures were based on b-cristobalite, orthotridymite, b-tridymite, and rutile crystals. The analysis of the electronic structure has been validated by many-body perturbation calculations using the G0W0 and GW + Bethe-Salpeter equation approximations, in order to account for quasi-particle and excitonic effects. The calculations indicate that many of these nanowires have semiconducting character, while the corresponding bulk solids are insulators. In the ca…
In ferromagnetic nanostructures, the ballistic anisotropic magnetoresistance (BAMR) is a change in the ballistic conductance with the direction of magnetization due to spin-orbit interaction. Very recently, a directional dependent ballistic conductance has been predicted to occur in a number of newly synthesized nonmagnetic semiconducting nanostructures subject to externally applied magnetic fields, without necessitating spin-orbit coupling. In this article, we review past works on the prediction of this BAMR effect in core-shell nanowires and rolled-up nanotubes. This is complemented by new r…
Hybrid semiconducting nanowire devices combining epitaxial superconductor and ferromagnetic insulator layers have been recently explored experimentally as an alternative platform for topological superconductivity at zero applied magnetic field. In this proof-of-principle work we show that the topological regime can be reached in actual devices depending on some geometrical constraints. To this end, we perform numerical simulations of InAs wires in which we explicitly include the superconducting Al and magnetic EuS shells, as well as the interaction with the electrostatic environment at a self-…
In a recent high-quality experimental work on normal metal--superconducting nanowire junctions arXiv:1807.01940 (2018), strong anisotropic suppression of induced superconductivity has been observed in tunnel conductance measurements in the presence of applied magnetic field with variable orientation. Following this finding, we investigate theoretically the dependence of tunnel conductance on the direction of the Zeeman field in order to understand the operational mechanisms and to extract effective system parameters. Second, motivated by a generic discrepancy between experiment and theory, i.e…
Semiconducting nanowire (NW) devices have garnered attention in self-powered electronic and optoelectronic applications. This work explores and exhibits, for the first time for visible light, a clear evidence of the zero-biased optoelectronic switching in randomly dispersed Ge and Si NW networks. The test bench, on which the NWs were dispersed for optoelectronic characterization, was fabricated using standard CMOS fabrication process, and utilized metal contacts with dissimilar work functions - Al and Ni. The randomly dispersed NWs respond to light by exhibiting substantial photocurrents and, …
We theoretically study the differential conductance of a one-dimensional normal-superconductor-normal-superconductor (N-SNS) junction with a phase bias applied between the two superconductors. We consider specifically a junction formed by a spin-orbit coupled semiconducting nanowire with regions of the nanowire having superconducting pairing induced by a bulk $s$-wave superconductor. When the nanowire is tuned into a topologically non-trivial phase by a Zeeman field, it hosts zero-energy Majorana modes at its ends as well as at the interface between the two superconductors. The phase-dependent…
We consider electronic transport through semiconducting nanowires (W) with spin-orbit interaction (SOI), in a hybrid N-W-N setup where the wire is contacted by normal-metal leads (N). We investigate the conductance behavior of the system as a function of gate and bias voltage, magnetic field, wire length, temperature, and disorder. The transport calculations are performed numerically and are based on standard recursive Green's function techniques. In particular, we are interested in understanding if and how it is possible to deduce the strength of the SOI from the transport behavior. This is a…
Quantum dots inserted in semiconducting nanowires are a promising platform for the fabrication of single photon devices. However, it is difficult to fully comprehend the electro-optical behaviour of such quantum objects without correlated studies of the structural and optical properties on the same nanowire. In this work, we study the spectral tunability of the emission of a single quantum dot in a GaN nanowire by applying external bias. The nanowires are dispersed and contacted on electron beam transparent Si3N4 membranes, so that transmission electron microscopy observations, photocurrent an…
Sub-gap states in semiconducting-superconducting nanowire hybrid devices are controversially discussed as potential topologically non-trivial quantum states. One source of ambiguity is the lack of an energetically and spatially well defined tunnel spectrometer. Here, we use quantum dots directly integrated into the nanowire during the growth process to perform tunnel spectroscopy of discrete sub-gap states in a long nanowire segment. In addition to sub-gap states with a standard magnetic field dependence, we find topologically trivial sub-gap states that are independent of the external magneti…
We study the magnetic and superconducting proximity effects in a semiconducting nanowire (NW) attached to superconducting leads and a ferromagnetic insulator (FI). We show that a sizable equilibrium spin polarization arises in the NW due to the interplay between the superconducting correlations and the exchange field in the FI. The resulting magnetization has a nonlocal contribution that spreads in the NW over the superconducting coherence length and is opposite in sign to the local spin polarization induced by the magnetic proximity effect in the normal state. For a Josephson-junction setup, …
Coupling a semiconducting nanowire to a microwave cavity provides a powerfull means to assess the presence or absence of isolated Majorana fermions in the nanowire. These exotic bound states can cause a significant cavity frequency shift but also a strong cavity nonlinearity leading for instance to light squeezing. The dependence of these effects on the nanowire gate voltages gives direct signatures of the unique properties of Majorana fermions, such as their self-adjoint character and their exponential confinement.
