We investigate the electronic properties of ballistic planar Josephson junctions with multiple superconducting terminals. Our devices consist of monolayer graphene encapsulated in boron nitride with ...molybdenum–rhenium contacts. Resistance measurements yield multiple resonant features, which are attributed to supercurrent flow among adjacent and nonadjacent Josephson junctions. In particular, we find that superconducting and dissipative currents coexist within the same region of graphene. We show that the presence of dissipative currents primarily results in electron heating and estimate the associated temperature rise. We find that the electrons in encapsulated graphene are efficiently cooled through the electron–phonon coupling.
Mobile phones, tablets, and other devices with capacitive touchscreens are ubiquitous in modern society. Consequently, the battery health of such devices along with the potential public health ...impacts of their typical use is of high importance. Here, we investigate the AC electric field present near the touchscreen surface during device charging. Using a Trifield TF2 meter for magnitude and a Faraday pickup coil for frequency, we study the AC electric field at the surface of an Apple iPhone 8 mobile phone in the 0–200 kHz range, well below the uplink/downlink bands used for cellular signals. We find the addition of the frequency content throughout this range and with integrated magnitude of the order of 500 V/m rms under certain phone charging conditions. Our findings suggest that the field is being generated by the lithium-ion battery. We note also that these AC electric fields are not present when the device is charged from a portable power bank.
The efficiency of organic solar cells can be increased by careful control of the nanoscale morphology of a dispersed bulk heterojunction device. Atomic force microscopy (AFM) has often been used to ...characterize morphology but debate persists over the value of traditional AFM measurements since the technique only addresses the active layer topography, and provides insufficient contrast to differentiate between components in a well-mixed composite. Using newer Kelvin Probe Force Microscopy (KPFM) and Quantitative Nanomechanical Mapping (QNM) modes, we demonstrate contrast due to differing elastic modulus and surface potentials between donor and acceptor materials and highlight the value of these techniques to understand critical materials properties as part of a comprehensive nanomorphology study. We test the value of our approach using blends of each of two anilinic squaraines with phenyl-C61-butyric acid methylester. These two squaraine materials differ in chemical compatibility with the standard fullerene acceptor. We vary annealing conditions for our blended films and use the described AFM approaches to demonstrate changing domain sizes, which are affected by chemical compatibility with the fullerene. We demonstrate how KPFM measurements go beyond QNM to provide contrast between materials with reproducibility at a higher image resolution. With the ability to measure contrast between donor and acceptor material, we make a strong case for non-destructive microscopy data to measure effects of variations in annealing temperature on squaraine film morphology, which we confirm influences device performance and efficiency. These conclusions are important for informing material selection for long-term use of associated commercial devices in the field.
•Two squaraine compounds are blended with a fullerene for organic solar cells.•Mechanical and electrical property maps characterize morphology of the films.•Domain size increases when chemical compatibility with the fullerene lessens.•Film annealing conditions are varied, also impacting domain size.
We present a study of a graphene-based Josephson junction with dedicated side gates carved from the same sheet of graphene as the junction itself. These side gates are highly efficient and allow us ...to modulate carrier density along either edge of the junction in a wide range. In particular, in magnetic fields in the 1- to 2-T range, we are able to populate the next Landau level, resulting in Hall plateaus with conductance that differs from the bulk filling factor. When counter-propagating quantum Hall edge states are introduced along either edge, we observe a supercurrent localized along that edge of the junction. Here, we study these supercurrents as a function of magnetic field and carrier density.
In this study, we examine multiple encapsulated graphene Josephson junctions to determine which mechanisms may be responsible for the supercurrent observed in the quantum Hall (QH) regime. ...Rectangular junctions with various widths and lengths were studied to identify which parameters affect the occurrence of QH supercurrent. We also studied additional samples where the graphene region is extended beyond the contacts on one side, making that edge of the mesa significantly longer than the opposite edge. This is done in order to distinguish two potential mechanisms: (a) supercurrents independently flowing along both non-contacted edges of graphene mesa, and (b) opposite sides of the mesa being coupled by hybrid electron–hole modes flowing along the superconductor/graphene boundary. The supercurrent appears suppressed in extended junctions, suggesting the latter mechanism.
The vanishing band gap of graphene has long presented challenges for making high-quality quantum point contacts (QPCs)the partially transparent p–n interfaces introduced by conventional split gates ...tend to short circuit the QPCs. This complication has hindered the fabrication of graphene quantum Hall Fabry–Pérot interferometers, until recent advances have allowed split-gate QPCs to operate utilizing the highly resistive ν = 0 state. Here, we present a simple recipe to fabricate QPCs by etching a narrow trench in the graphene sheet to separate the conducting channel from self-aligned graphene side gates. We demonstrate operation of the individual QPCs in the quantum Hall regime and further utilize these QPCs to create and study a quantum Hall interferometer.
The tendency of aerosols to carry viral particles featured significantly in public discourse during the SARS Covid-19 pandemic. In this research, the potential significance of the aerosol electric ...charge, especially as it relates to indoor relative humidity (RH) is considered. While electrostatic interactions may occur at any level of humidity, the level of humidity has a strong influence on these interactions. Above 55 % RH, there is sufficient moisture in the air to facilitate neutralization of the electric charges of particles and surfaces, whereas, at lower humidity levels, less moisture and higher surface resistivities enable increasingly stronger electrostatic interactions. Experiments were designed and conducted to study the behavior of electrically charged aerosols in fields emanating from capacitive touchscreens and permanent magnets. These preliminary experimental results suggest that operating indoor environments closer to the 55–60 % RH range could reduce interactions between these charged aerosols and capacitive touchscreens. This relative humidity range is within the acceptable ranges of humidity recommended by ASHRAE standard 55 which defines thermal environmental conditions for human occupancy.
•High surface resistivity and low moisture strengthens electrostatics at low relative humidity (RH < 50 %).•AC electric fields on the order of ∼500 V/m RMS were measured on phones charging on a wall charger.•The effective DC electrostatic charge, as measured by a Faraday pail, appears to be higher during charging.•Preliminary experiments show that these electric and magnetic fields may be interacting with charged aerosol streams.•Suggestions for better mobile phone hygiene are provided to minimize any potential risk.
Multiterminal Inverse AC Josephson Effect Arnault, Ethan G; Larson, Trevyn F. Q; Seredinski, Andrew ...
Nano letters,
11/2021, Letnik:
21, Številka:
22
Journal Article
Recenzirano
Odprti dostop
When a Josephson junction is exposed to microwave radiation, it undergoes the inverse AC Josephson effectthe phase of the junction locks to the drive frequency. As a result, the I–V curves of the ...junction acquire “Shapiro steps” of quantized voltage. If the junction has three or more superconducting contacts, coupling between different pairs of terminals must be taken into account and the state of the junction evolves in a phase space of higher dimensionality. Here, we study the multiterminal inverse AC Josephson effect in a graphene sample with three superconducting terminals. We observe robust fractional Shapiro steps and correlated switching events, which can only be explained by considering the device as a completely connected Josephson network. We successfully simulate the observed behaviors using a modified two-dimensional RCSJ model. Our results suggest that multiterminal Josephson junctions are a playground to study highly connected nonlinear networks with novel topologies.
The coupling of a superconductor to topological states is expected to bring about non-abelian excitations which may enable fault-tolerant quantum computing. The observation of supercurrent in hybrid ...superconductor / quantum Hall devices was an important step towards the realization of these modes in a gate- and field- tunable platform. However, early studies of quantum Hall supercurrent led to ambiguity regarding the microscopic mechanism at play, leaving doubt as to whether this current was nontrivial. This work sheds light on the mechanisms by which supercurrent is mediated in graphene Josephson junctions at both low and high magnetic fields through interference measurements. Magnetic interference patterns provide information about the spatial distribution of supercurrent and their periodicity can serve as an indication of nontrivial behavior. Anomalous interference patterns observed around zero field hint at undiscovered graphene physics. At higher fields, unchanged patterns in devices with thin trenches provide evidence that quantum Hall supercurrent in traditional graphene Josephson junctions is mediated by trivial states at the vacuum edge. This motivates distancing vacuum edges from superconducting leads and the introduction of efficient, native graphene side gates. These enable the induction of local quantum Hall states, which are shown via interference patterns to independently carry supercurrent - the most persuasive evidence to date of supercurrent mediated by quantum Hall edge states.
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