A. K. Ott

Atomically thin quantum light-emitting diodes

Transition metal dichalcogenides are optically active, layered materials promising for fast optoelectronics and on-chip photonics. We demonstrate electrically driven single-photon emission from localized sites in tungsten diselenide and tungsten disulphide. To achieve this, we fabricate a light-emitting diode structure comprising single-layer graphene, thin hexagonal boron nitride and transition metal dichalcogenide mono- and bi-layers. Photon correlation measurements are used to confirm the single-photon nature of the spectrally sharp emission. These results present the transition metal dichalcogenide family as a platform for hybrid, broadband, atomically precise quantum photonics devices.

Large-scale quantum-emitter arrays in atomically thin semiconductors

Quantum light emitters have been observed in atomically thin layers of transition metal dichalcogenides. However, they are found at random locations within the host material and usually in low densities, hindering experiments aiming to investigate this new class of emitters. Here, we create deterministic arrays of hundreds of quantum emitters in tungsten diselenide and tungsten disulphide monolayers, emitting across a range of wavelengths in the visible spectrum (610–680 nm and 740–820 nm), with a greater spectral stability than their randomly occurring counterparts. This is achieved by depositing monolayers onto silica substrates nanopatterned with arrays of 150-nm-diameter pillars ranging from 60 to 190 nm in height. The nanopillars create localized deformations in the material resulting in the quantum confinement of excitons. Our method may enable the placement of emitters in photonic structures such as optical waveguides in a scalable way, where precise and accurate positioning is paramount.

p-wave triggered superconductivity in single layer graphene on an electron-doped oxide superconductor

Electron pairing in the vast majority of superconductors follows the Bardeen–Cooper–Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.

Graphene-silicon phase modulators with gigahertz bandwidth

V. Sorianello, M. Midrio,G. Contestabile,I. Asselberg,J. Van Campenhout,C. Huyghebaerts,I. Goykhman,A. K. Ott,A. C. Ferrari,M.Romagnoli Consorzio Nazionale per le Telecomunicazioni (CNIT), National Laboratory of Photonic Networks, Via G. Moruzzi 1, 56124 Pisa, Italy Consorzio Nazionale per le Telecomunicazioni (CNIT), University of Udine, Via delle Scienze 206, 33100 Udine, Italy Consorzio Nazionale per le Telecomunicazioni (CNIT), Scuola Superiore Sant’Anna, via G. Moruzzi 1, 56124 Pisa, Italy IMEC, Kapeldreef 75, 3001 Leuven, Belgium Cambridge Graphene Centre, Cambridge University, 9 JJ Thomson Avenue, Cambridge CB3 OFA, UK

Carbon-Based Resistive Memories

Carbon-based nonvolatile resistive memories are an emerging technology. Switching endurance remains a challenge in carbon memories based on tetrahedral amorphous carbon (ta-C). One way to counter this is by oxygenation to increase the repeatability of reversible switching. Here, we overview the current status of carbon memories. We then present a comparative study of oxygen-free and oxygenated carbon-based memory devices, combining experiments and molecular dynamics (MD) simulations.

Broadband, electrically tunable third-harmonic generation in graphene

Optical harmonic generation occurs when high intensity light (>1010 W m–2) interacts with a nonlinear material. Electrical control of the nonlinear optical response enables applications such as gate-tunable switches and frequency converters. Graphene displays exceptionally strong light–matter interaction and electrically and broadband tunable third-order nonlinear susceptibility. Here, we show that the third-harmonic generation efficiency in graphene can be increased by almost two orders of magnitude by controlling the Fermi energy and the incident photon energy. This enhancement is due to logarithmic resonances in the imaginary part of the nonlinear conductivity arising from resonant multiphoton transitions. Thanks to the linear dispersion of the massless Dirac fermions, gate controllable third-harmonic enhancement can be achieved over an ultrabroad bandwidth, paving the way for electrically tunable broadband frequency converters for applications in optical communications and signal processing.Gate tunable and ultrabroadband third-harmonic generation can be achieved in graphene, paving the way for electrically tunable broadband frequency converters for applications in optical communications and signal processing.

Joule heating effects in nanoscale carbon-based memory devices

One of the emerging candidates to bridge the gap between fast but volatile DRAM and non-volatile but slow storage devices is tetrahedral amorphous carbon (ta-C) based memory [1]-[3]. This offers a very good scalability, data retention and sub-5ns switching [2], [3]. Amorphous carbon memory devices can be electrically and optically switched from a high resistance state (HRS) to a low resistance state (LRS) [4]. The electrical conduction in the LRS is thought to be through sp2 clusters that form a conductive filament [4].

Tetrahedral amorphous carbon resistive memories with graphene-based electrodes

Resistive-switching memories are alternative to Si-based ones, which face scaling and high power consumption issues. Tetrahedral amorphous carbon (ta-C) shows reversible, non-volatile resistive switching. Here we report polarity independent ta-C resistive memory devices with graphene-based electrodes. Our devices show ON/OFF resistance ratios

Phonon anomalies in Graphene induced by highly excited charge carriers

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Corrigendum: p -wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor

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