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Electrons in two dimensions and strong magnetic fields can form an insulating two-dimensional system with conducting one-dimensional channels along the edge. Electron interactions in these edges can lead to independent transport of charge and heat, even in opposite directions. Here, we heat the outer edge of such a quantum Hall system using a quantum point contact. By placing quantum dots upstream and downstream from the heater, we measure both the chemical potential and temperature of that edge to study charge and heat transport, respectively. We find that charge is transported exclusively downstream, but heat can be transported upstream when the edge has additional structure related to fractional quantum Hall (FQH) physics. Surprisingly, this can occur even when the bulk is in an integer quantum Hall state and the edge contains no signatures of FQH charge transport. We also find an unexpected bulk contribution to heat transport at ν  = 1. In most electrical conductors, heat is transported by charge carriers and so both usually flow in the same direction; but in two-dimensional electron systems subject to strong magnetic fields, certain fractional quantum Hall states can cause charge and heat to flow in opposite directions.

Conventional s -wave superconductivity arises from singlet pairing of electrons with opposite Fermi momenta, forming Cooper pairs with zero net momentum. Recent studies have focused on coupling s -wave superconductors to systems with an unusual configuration of electronic spin and momentum at the Fermi surface, where the nature of the paired state can be modified and the system may even undergo a topological phase transition. Here we present measurements and theoretical calculations of HgTe quantum wells coupled to aluminium or niobium superconductors and subject to a magnetic field in the plane of the quantum well. We find that this magnetic field tunes the momentum of Cooper pairs in the quantum well, directly reflecting the response of the spin-dependent Fermi surfaces. In the high electron density regime, the induced superconductivity evolves with electron density in agreement with our model based on the Hamiltonian of Bernevig, Hughes and Zhang. This agreement provides a quantitative value for g ̃/ v F , where g ̃ is the effective g -factor and v F is the Fermi velocity. Our new understanding of the interplay between spin physics and superconductivity introduces a way to spatially engineer the order parameter from singlet to triplet pairing, and in general allows investigation of electronic spin texture at the Fermi surface of materials. The interplay between spin physics and superconductivity is examined in HgTe quantum wells, revealing a tunable momentum of the Cooper pairs that drives changes in their superconducting behaviour.

•Viral infectivity methods are often slow, tedious, labor intensive, and difficult to standardize.•Laser Force Cytology uses optical and fluidic forces to quantify cellular changes upon infection.•Non-subjective measurements were made in 16 h that correlated with TCID50 results requiring 72 h.•Real-time Laser Force Cytology based measurements were correlated with TCID50 of the supernatant.•Rapid infectivity measurements can improve vaccine research, development and manufacturing. The ability to rapidly and accurately determine viral infectivity can help improve the speed of vaccine product development and manufacturing. Current methods to determine infectious viral titers, such as the end-point dilution (50% tissue culture infective dose, TCID50) and plaque assays are slow, labor intensive, and often subjective. In order to accelerate virus quantification, Laser Force Cytology (LFC) was used to monitor vesicular stomatitis virus (VSV) infection in Vero (African green monkey kidney) cells. LFC uses a combination of optical and fluidic forces to interrogate single cells without the use of labels or antibodies. Using a combination of variables measured by the Radiance™ LFC instrument (LumaCyte), an infection metric was developed that correlates well with the viral titer as measured by TCID50 and shortens the timeframe from infection to titer determination from 3 days to 16 h (a 4.5 fold reduction). A correlation was also developed between in-process cellular measurements and the viral titer of collected supernatant, demonstrating the potential for real-time infectivity measurements. Overall, these results demonstrate the utility of LFC as a tool for rapid infectivity measurements throughout the vaccine development process.

Topological superconductors can support localized Majorana states at their boundaries 1 – 5 . These quasi-particle excitations obey non-Abelian statistics that can be used to encode and manipulate quantum information in a topologically protected manner 6 , 7 . Although signatures of Majorana bound states have been observed in one-dimensional systems, there is an ongoing effort to find alternative platforms that do not require fine-tuning of parameters and can be easily scaled to large numbers of states 8 – 21 . Here we present an experimental approach towards a two-dimensional architecture of Majorana bound states. Using a Josephson junction made of a HgTe quantum well coupled to thin-film aluminium, we are able to tune the transition between a trivial and a topological superconducting state by controlling the phase difference across the junction and applying an in-plane magnetic field 22 . We determine the topological state of the resulting superconductor by measuring the tunnelling conductance at the edge of the junction. At low magnetic fields, we observe a minimum in the tunnelling spectra near zero bias, consistent with a trivial superconductor. However, as the magnetic field increases, the tunnelling conductance develops a zero-bias peak, which persists over a range of phase differences that expands systematically with increasing magnetic field. Our observations are consistent with theoretical predictions for this system and with full quantum mechanical numerical simulations performed on model systems with similar dimensions and parameters. Our work establishes this system as a promising platform for realizing topological superconductivity and for creating and manipulating Majorana modes and probing topological superconducting phases in two-dimensional systems. Majorana bound states are created in a two-dimensional architecture by confining Majorana channels within a planar Josephson junction, using the phase difference across the junction and an in-plane magnetic field.

Majorana fermions, which are their own antiparticles, are expected to exist in topological superconductors. A study using superconducting leads in contact with a quantum well reveals the presence of supercurrents along one-dimensional sample edges of a quantum spin Hall state. These edge supercurrents are topological. Topological insulators are a newly discovered phase of matter characterized by gapped bulk states surrounded by conducting boundary states 1 , 2 , 3 . Since their theoretical discovery, these materials have encouraged intense efforts to study their properties and capabilities. Among the most striking results of this activity are proposals to engineer a new variety of superconductor at the surfaces of topological insulators 4 , 5 . These topological superconductors would be capable of supporting localized Majorana fermions, particles whose braiding properties have been proposed as the basis of a fault-tolerant quantum computer 6 . Despite the clear theoretical motivation, a conclusive realization of topological superconductivity remains an outstanding experimental goal. Here we present measurements of superconductivity induced in two-dimensional HgTe/HgCdTe quantum wells, a material that becomes a quantum spin Hall insulator when the well width exceeds d C  = 6.3 nm (ref.  7 ). In wells that are 7.5 nm wide, we find that supercurrents are confined to the one-dimensional sample edges as the bulk density is depleted. However, when the well width is decreased to 4.5 nm the edge supercurrents cannot be distinguished from those in the bulk. Our results provide evidence for supercurrents induced in the helical edges of the quantum spin Hall effect, establishing this system as a promising avenue towards topological superconductivity. In addition to directly confirming the existence of the topological edge channels, our results also provide a measurement of their widths, which range from 180 nm to 408 nm.

The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a two-dimensional system. A superconductor (SC) contacting these states can provide correlations of the quasiparticles in the dissipationless edge states. Here we fabricated highly transparent and nanometre-scale SC junctions to graphene. We demonstrate that the QH edge states can couple via superconducting correlations through the SC electrode narrower than the superconducting coherence length. We observe that the chemical potential of the edge state exhibits a sign reversal across the SC electrode. This provides direct evidence of conversion of the incoming electron to the outgoing hole along the chiral edge state, termed crossed Andreev conversion (CAC). We show that CAC can successfully describe the temperature, bias and SC electrode width dependences. This hybrid SC/QH system could provide a novel route to create isolated non-Abelian anyonic zero modes, in resonance with the chiral edge states. A superconductor–graphene junction is shown to exhibit the quantum Hall effect, with the chemical potential of the edge state displaying a sign reversal. Such a system could provide a platform for observing isolated non-Abelian anyonic zero modes.

There are many good reasons to make a tiling around some discrete set of points. For example, maybe you need to know what regions are served by some set of post offices or cell phone satellites. Once you have a tiling, there are many reasons to define a point set with it. For instance, you might want to decorate each tile with a few points to create or destroy symmetry, or to obtain combinatorial information. Since you can go from point sets to tilings and back again, you might come across some interesting ways to associate one set of points to another. Once you have a map from a class of objects back to itself, you can take a dynamical systems viewpoint to analyze the situation. This paper does exactly that, with a new dynamical system based on the vertices of Voronoï tessellations.

Charge-transport models are usually developed by first finding an appropriate density of states (DOS) which is extracted from experimental data. For organic materials, two of the more common ones include the Gaussian density of states and the exponential density of states (EDOS). This article will focus on the latter. Charge-transport models which employ an EDOS have been extensively researched, and many articles are still being published. However, from an analytical point of view, only approximate mathematical expressions for the charge carrier density are ever used. This, in general, forces a charge-transport model to be valid only within a limited temperature range. This article illustrates a more mathematically exact way to handle an organic semiconductor whose DOS can be represented by an exponential function.

A small volume flowcell for fluorescence detection in capillary flow injection (CFI) analysis has been created by using a low cost, commercially available fluidic device. Fluorescence detection is achieved using an optical fiber to deliver excitation light to the sample flowing through the device and another optical fiber to collect fluorescence emission. The flowcell is a standard fluidic cross with a swept volume of 721 nL. Optical fibers were oriented at right angles using standard sleeves and ferrules to set their position near the cross intersection. Multiple excitation sources were used including a low power UV laser and blue and UV light emitting diodes (LED). The full emission spectrum detection limits, using the laser, for fluorescein and bovine serum albumin (BSA) were 0.30 ppb and 2.1 x 10(-4)% (w/w), respectively. Two fluidic crosses were used in series for multi-wavelength fluorescence excitation using fiber-optically coupled LED.