Crystal defects can confine isolated electronic spins and are promising candidates for solid-state quantum information. Alongside research focusing on nitrogen-vacancy centres in diamond, an alternative strategy seeks to identify new spin systems with an expanded set of technological capabilities, a materials-driven approach that could ultimately lead to ‘designer’ spins with tailored properties. Here we show that the 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states, including states in all three with room-temperature quantum coherence. The prevalence of this spin coherence shows that crystal polymorphism can be a degree of freedom for engineering spin qubits. Long spin coherence times allow us to use double electron–electron resonance to measure magnetic dipole interactions between spin ensembles in inequivalent lattice sites of the same crystal. Together with the distinct optical and spin transition energies of such inequivalent states, these interactions provide a route to dipole-coupled networks of separately addressable spins.

The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries 1

We study photodetection in graphene near a local electrostatic gate, which enables active control of the potential landscape and carrier polarity. We find that a strong photoresponse only appears when and where a p-n junction is formed, allowing on-off control of photodetection.Photocurrents generated near p-n junctions do not require biasing and can be realized using submicron gates. Locally modulated photoresponse enables a new range of applications for graphene-based photodetectors including, for example, pixilated infrared imaging with control of response on subwavelength dimensions. MANUSCRIPT TEXTGraphene is a promising photonic material 1 whose gapless band structure allows electron-hole pairs to be generated over a broad range of wavelengths, from UV, visible 2 , and telecommunication bands, to IR and THz frequencies 3 . Previous studies of photocurrents in graphene have demonstrated photoresponse near metallic contacts [4][5][6][7] , at the interface between single-layer and bilayer regions 8 , or at the edge of chemically doped regions 10 . Photocurrents generated near metal contacts were attributed to electric fields in the graphene that arise from band bending near the contacts 5-7 , and could be modulated by sweeping a global back-gate voltage with the potential of the contacts fixed. In these studies, photocurrent away from contacts and interfaces was typically very weak. In contrast, the present study concerns devices with top gates, separated from otherwise homogeneous graphene by an insulator, Al2O3, deposited by atomic layer deposition (ALD). When the top gate inverts the carrier type under the gate, a p-n junction is formed at the gate edges, and a highly localized photocurrent is observed using a 1 * These authors contributed equally to this work. focussed scanning laser. A density difference induced by the top gate that does not create a p-n junction does not create local photosensitivity.Comparing experimental results to theory suggests that the photocurrent generated at the p-n interface results from a combination of direct photogeneration of electron-hole pairs in a potential gradient, and a photothermoelectric effect in which electric fields result from optically induced temperature gradients 8,11 . Both effects are strongly enhanced at p-n interfaces: The enhancement of direct photocurrent results from its scaling inversely with local conductivity, while the thermoelectric contribution is enhanced by the strong spatial dependence of the Seebeck coefficient near the p-n interface. As neither mechanism is wavelength selective, the overall effect should provide broadband photosensitivity. We further anticipate that the ability to activate local photosensitive regions using gate voltages will provide pixel-controlled bolometers for imaging or spectroscopy with broadband sensitivity and subwavelength spatial resolution.A typical device layout and micrograph are shown in Fig. 1. Graphene was deposited onto ~300 nm of silicon dioxide on degenerately doped silicon by mechanical exfoliat...

* These authors contribute equally to this work.Photonic circuits can be much faster than their electronic counterparts, but they are difficult to miniaturize below the optical wavelength scale. Nanoscale photonic circuits based on surface plasmon polaritons (SPs) are a promising solution to this problem because they can localize light below the diffraction limit 1-8 . However, there is a general tradeoff between the localization of an SP and the efficiency with which it can be detected with conventional far-field optics. Here we describe a new all-electrical SP detection technique based on the near-field coupling between guided plasmons and a nanowire field-effect transistor. We use our detectors to electrically detect the plasmon emission from an individual colloidal quantum dot coupled to an SP waveguide. The detectors are both nanoscale and highly efficient (0.1 electrons/plasmon), and a plasmonic gating effect can be used to amplify the signal even higher (up to 50 electrons/plasmon). These results enable new on-chip optical sensing applications and fulfill a key requirement for "dark" optoplasmonic nanocircuits in which SPs can be generated, manipulated, and detected without involving far-field radiation.2 SPs are charge-density waves that propagate along metal-dielectric interfaces. They can be concentrated and guided by current carrying wires, suggesting an integrated approach to optical and electrical signal processing. Our near-field plasmon detection scheme consists of an Ag nanowire (NW) crossing a Ge NW field-effect transistor (Fig. 1, Methods). The Ag NW guides 10 SPs to the Ag/Ge junction, where they are converted to electron-hole (e-h) pairs 11-13 and detected as current through the Ge NW. The Ag NWs are highly crystalline and defect-free 8,14,15 , allowing SPs to propagate over distances of several microns without scattering into free-space photons. The Ge NWs are lightly p-doped, covered with a thin native oxide layer, and sensitive to visible light 16 .Electrical plasmon detection is demonstrated by scanning a focused laser beam across an Ag/Ge crossbar device and recording the current (I) through the Ge NW as a function of the diffraction-limited laser spot position. These data, recorded at V b = V gate = 0, show that current flows through the Ge NW only when the laser beam is focused on four distinct spots on the device (Fig. 1b). First, current is detected when the laser is focused near the Ag/Ge junction, due to the direct photoresponse of the Ge NW 16 . The photocurrent induced on the left (I left ) and right (I right ) sides of the junction have opposite signs (discussed below). Moreover, current through the Ge NW (I plas ) is recorded when the laser is focused at either end of the Ag NW.This I plas signal is the key signature for electrical SP detection. Propagating SPs can be launched in the Ag NW only when the excitation laser is incident on the Ag NW ends 15 . Away from the ends, free space photon-to-SP conversion is strongly suppressed by the wave vector mismatch between the two ...