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Insights into the fundamental properties of graphene's Dirac-Weyl fermions have emerged from studies of electron tunnelling transistors in which an atomically thin layer of hexagonal boron nitride (hBN) is sandwiched between two layers of high purity graphene. Here, we show that when a single defect is present within the hBN tunnel barrier, it can inject electrons into the graphene layers and its sharply defined energy level acts as a high resolution spectroscopic probe of electron-electron interactions in graphene. We report a magnetic field dependent suppression of the tunnel current flowing through a single defect below temperatures of ~2 K. This is attributed to the formation of a magnetically-induced Coulomb gap in the spectral density of electrons tunnelling into graphene due to electron-electron interactions. Electron-electron interactions are known to play an important role in the in-plane transport properties of graphene-based devices. Here, the authors investigate the role of electron-electron interactions on electrons tunnelling between the layers of a graphene/hBN/graphene tunnel transistor and demonstrate the emergence of a Coulomb gap at low temperatures and in quantising magnetic fields. [ABSTRACT FROM AUTHOR]

The quantum Hall effect is widely used for the investigation of fundamental phenomena, ranging from topological phases to composite fermions. In particular, the discovery of a room temperature resistance quantum in graphene is significant for compact resistance standards that can operate above cryogenic temperatures. However, this requires large magnetic fields that are accessible only in a few high magnetic field facilities. Here, we report on the quantum Hall effect in graphene encapsulated by the ferroelectric insulator CuInP2S6. Electrostatic gating of the graphene channel enables the Fermi energy to be tuned so that electrons in the localized states of the insulator are in equilibrium with the current-carrying, delocalized states of graphene. Due to the presence of strongly bound states in this hybrid system, a quantum Hall plateau is observed over a wide range of temperatures in relatively modest magnetic fields. The quantum Hall effect has had a profound impact on solid-state physics and has been investigated using different two-dimensional systems, including graphene. Here, the authors investigate graphene encapsulated by a ferroelectric insulator, CuInP2S6, where they observe a quantum Hall effect that endures over a wide temperature range in relatively modest magnetic fields. [ABSTRACT FROM AUTHOR]

Developments in semiconductor science have led to the miniaturization and improvement of light detection technologies for many applications. However, traditional pn-junctions or three-dimensional device geometries for detection of ultraviolet (UV) light are still limited by the physical properties of the semiconductors used, such as the small penetration depth of UV light in silicon. Van der Waals (vdW) semiconductors and their pn-junctions can offer an alternative solution due to their optical properties and thin pn-junction region. Here, we report on a multi-layer junction that combines single layer graphene and vdW semiconductors (p-GaSe and n-In2Se3) with strong optical absorption in the UV range. The junctions have broadband spectral response (0.3-1.0 μm) and high photoresponsivity under forward and reverse bias, or without any externally applied voltage. The photoresponse differs from that of a traditional pn-junction diode as it is governed by charge transport across thin layers and light-current conversion at three vdW interfaces (e.g. the graphene/GaSe, GaSe/In2Se3 and In2Se3/graphene interfaces). The type-II band alignment at the GaSe/In2Se3 interface and electric field at the three vdW interfaces are beneficial to suppress carrier recombination for enhanced photoresponsivity (up to ~102 A/W) and detectivity (up to ~1013 Jones), beyond conventional UV-enhanced silicon detection technology. [ABSTRACT FROM AUTHOR]

Pristine graphene and graphene-based heterostructures can exhibit exceptionally high electron mobility if their surface contains few electron-scattering impurities. Mobility directly influences electrical conductivity and its dependence on the carrier density. But linking these key transport parameters remains a challenging task for both theorists and experimentalists. Here, we report numerical and analytical models of carrier transport in graphene, which reveal a universal connection between graphene's carrier mobility and the variation of its electrical conductivity with carrier density. Our model of graphene conductivity is based on a convolution of carrier density and its uncertainty, which is verified by numerical solution of the Boltzmann transport equation including the effects of charged impurity scattering and optical phonons on the carrier mobility. This model reproduces, explains, and unifies experimental mobility and conductivity data from a wide range of samples and provides a way to predict a priori all key transport parameters of graphene devices. Our results open a route for controlling the transport properties of graphene by doping and for engineering the properties of 2D materials and heterostructures. Graphene exhibits both extremely high electrical conductivity and electron mobility but an incomplete understanding of the underlying mechanisms so far limits potential applications in electrical devices. Here, the authors theoretically and experimentally investigate the role of charged impurities and optical phonons on the conductivity properties of graphene and establish a universal connection between the mobility and conductivity. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdW) crystals have attracted considerable interest for digital electronics beyond Si-based complementary metal oxide semiconductor technologies. Despite the transformative success of Si-based devices, there are limits to their miniaturization and functionalities. Here we realize a resonant tunnelling transistor (RTT) based on a 2D InSe layer sandwiched between two multilayered graphene (MLG) electrodes. In the RTT the energy of the quantum-confined 2D subbands of InSe can be tuned by the thickness of the InSe layer. By applying a voltage across the two MLG electrodes, which serve as the source and drain electrodes to the InSe, the chemical potential in the source can be tuned in and out of resonance with a given 2D subband, leading to multiple regions of negative differential conductance that can be additionally tuned by electrostatic gating. This work demonstrates the potential of InSe and InSe-based RTTs for applications in quantum electronics. Limits on the functionality and miniaturization of Si-based devices present barriers towards integration into quantum electronics. The authors present an alternative, resonant tunnelling transistor based on a two-dimensional layered heterostructure, exhibiting multiple regions of negative differential conductance. [ABSTRACT FROM AUTHOR]

We report on an example of confined magnetic ions with long spin coherence near room temperature. This was achieved by confining single Mn2+ spins in colloidal semiconductor quantum dots (QDs) and by dispersing the QDs in a proton-spin free matrix. The controlled suppression of Mn-Mn interactions and minimization of Mn-nuclear spin dipolar interactions result in unprecedentedly long phase memory (TM ~ 8 μs) and spin-lattice relaxation (T1 ~ 10 ms) time constants for Mn2+ ions at T = 4.5 K, and in electron spin coherence observable near room temperature (TM ~ 1 μs). [ABSTRACT FROM AUTHOR]