Dmitri K. Efetov

Specular interband Andreev reflections at van der Waals interfaces between graphene and NbSe2

D. K. Efetov, ∗ L. Wang, C. Handschin, K. B. Efetov, 4 J. Shuang, R. Cava, T. Taniguchi, K. Watanabe, J. Hone, C. R. Dean, and P. Kim † Department of Physics, Columbia University, New York, NY 10027, USA Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA Theoretische Physik III, Ruhr-Universität Bochum, D-44780 Bochum, Germany National University of Science and Technology “MISiS”, Moscow, 119049, Russia Department of Chemistry, Princeton University, Princeton, NJ 08544, USA National Institute for Materials Science, Namiki 1-1, Ibaraki 305-0044, Japan (Dated: May 20, 2015)

High-Responsivity Graphene-Boron Nitride Photodetector and Autocorrelator in a Silicon Photonic Integrated Circuit

Graphene and other two-dimensional (2D) materials have emerged as promising materials for broadband and ultrafast photodetection and optical modulation. These optoelectronic capabilities can augment complementary metal-oxide-semiconductor (CMOS) devices for high-speed and low-power optical interconnects. Here, we demonstrate an on-chip ultrafast photodetector based on a two-dimensional heterostructure consisting of high-quality graphene encapsulated in hexagonal boron nitride. Coupled to the optical mode of a silicon waveguide, this 2D heterostructure-based photodetector exhibits a maximum responsivity of 0.36 A/W and high-speed operation with a 3 dB cutoff at 42 GHz. From photocurrent measurements as a function of the top-gate and source-drain voltages, we conclude that the photoresponse is consistent with hot electron mediated effects. At moderate peak powers above 50 mW, we observe a saturating photocurrent consistent with the mechanisms of electron-phonon supercollision cooling. This nonlinear photoresponse enables optical on-chip autocorrelation measurements with picosecond-scale timing resolution and exceptionally low peak powers.

Tunable and high-purity room temperature single-photon emission from atomic defects in hexagonal boron nitride.

Two-dimensional van der Waals materials have emerged as promising platforms for solid-state quantum information processing devices with unusual potential for heterogeneous assembly. Recently, bright and photostable single photon emitters were reported from atomic defects in layered hexagonal boron nitride (hBN), but controlling inhomogeneous spectral distribution and reducing multi-photon emission presented open challenges. Here, we demonstrate that strain control allows spectral tunability of hBN single photon emitters over 6u2009meV, and material processing sharply improves the single photon purity. We observe high single photon count rates exceeding 7u2009×u2009106 counts per second at saturation, after correcting for uncorrelated photon background. Furthermore, these emitters are stable to material transfer to other substrates. High-purity and photostable single photon emission at room temperature, together with spectral tunability and transferability, opens the door to scalable integration of high-quality quantum emitters in photonic quantum technologies.Inhomogeneous spectral distribution and multi-photon emission are currently hindering the use of defects in layered hBN as reliable single photon emitters. Here, the authors demonstrate strain-controlled wavelength tuning and increased single photon purity through suitable material processing.

Probing the ultimate plasmon confinement limits with a van der Waals heterostructure

Light confined to a single atomic layer The development of nanophotonic technology is reliant on the ability to confine light to spatial dimensions much less than the wavelength of the light itself. Typically, however, in metal plasmonic approaches, there is a trade-off between confinement and losses. Alcaraz Iranzo et al. fabricated heterostructures comprising monolayers of graphene and hexagonal boron nitride (hBN) and an array of metallic rods. The light was confined vertically (as propagating plasmons) between the metal and the graphene, even when the insulating hBN spacer was just a single monolayer. Such heterostructures should provide a powerful and versatile platform for nanophotonics. Science, this issue p. 291 A heterostructure design confines light to a single atomic layer. The ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing, and nanoscale lasers. Although plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the length scale of one atom. This is achieved through far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric spacer between graphene and metal rods. A theoretical model that takes into account the nonlocal optical response of both graphene and metal is used to describe the results. These ultraconfined plasmonic modes, addressed with far-field light excitation, enable a route to new regimes of ultrastrong light-matter interactions.

Crossover from retro to specular Andreev reflections in bilayer graphene

Ongoing experimental progress in the preparation of ultraclean graphene/superconductor (SC) interfaces enabled the recent observation of specular interband Andreev reflections (ARs) at bilayer graphene

Ultrafast Graphene Light Emitters

(mathrm{BLG})/{mathrm{NbSe}}_{2}

Compact mid-infrared graphene thermopile enabled by a nanopatterning technique of electrolyte gates

van der Waals interfaces [Efetov et al., Nat. Phys. 12, 328 (2016)]. Motivated by this experiment we theoretically study the differential conductance across a BLG/SC interface at the continuous transition from high to ultralow Fermi energies

Tunable quantum emission from atomic defects in hexagonal boron nitride

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Self-aligned local electrolyte gating of 2D materials for mid-infrared photodetection

in BLG. Using the Bogoliubov-de Gennes equations and the Blonder-Tinkham-Klapwijk formalism we derive analytical expressions for the differential conductance across the BLG/SC interface. We find a characteristic signature of the crossover from intraband retro (high

Cavity-enhanced narrowband radiation of an electrically driven graphene light emitter

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