Selectively enhanced photocurrent generation in twisted bilayer graphene with van Hove singularity

Abstract

Graphene with ultra-high carrier mobility and ultra-short photoresponse time has shown remarkable potential in ultrafast photodetection. However, the broad and weak optical absorption (∼2.3%) of monolayer graphene hinders its practical application in photodetectors with high responsivity and selectivity. Here we demonstrate that twisted bilayer graphene, a stack of two graphene monolayers with an interlayer twist angle, exhibits a strong light-matter interaction and selectively enhanced photocurrent generation. Such enhancement is attributed to the emergence of unique twist-angle-dependent van Hove singularities, which are directly revealed by spatially resolved angle-resolved photoemission spectroscopy. When the energy interval between the van Hove singularities of the conduction and valance bands matches the energy of incident photons, the photocurrent generated can be significantly enhanced (up to ∼80 times with the integration of plasmonic structures in our devices). These results provide valuable insight for designing graphene photodetectors with enhanced sensitivity for variable wavelength.

ARTICLE

Received 1 Oct 2015 | Accepted 12 Jan 2016 | Published 7 Mar 2016

Jianbo Yin1,*, Huan Wang1,*, Han Peng2,*, Zhenjun Tan1,3, Lei Liao1, Li Lin1, Xiao Sun1,3, Ai Leen Koh4, Yulin Chen2, Hailin Peng1 & Zhongfan Liu1

Graphene with ultra-high carrier mobility and ultra-short photoresponse time has shown remarkable potential in ultrafast photodetection. However, the broad and weak optical absorption (B2.3%) of monolayer graphene hinders its practical application in photodetectors with high responsivity and selectivity. Here we demonstrate that twisted bilayer graphene, a stack of two graphene monolayers with an interlayer twist angle, exhibits a strong lightmatter interaction and selectively enhanced photocurrent generation. Such enhancement is attributed to the emergence of unique twist-angle-dependent van Hove singularities, which are directly revealed by spatially resolved angle-resolved photoemission spectroscopy. When the energy interval between the van Hove singularities of the conduction and valance bands matches the energy of incident photons, the photocurrent generated can be signicantly enhanced (up to B80 times with the integration of plasmonic structures in our devices). These results provide valuable insight for designing graphene photodetectors with enhanced sensitivity for variable wavelength.

DOI: 10.1038/ncomms10699 OPEN

Selectively enhanced photocurrent generation in twisted bilayer graphene with van Hove singularity

1 Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, 202 Chengfu Road, Haidian District, Beijing 100871, China. 2 Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK. 3 Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China. 4 Stanford Nano Shared Facilities, Stanford University, Stanford, California 94305, USA. * These authors contributed equally to this work. Correspondence and requests for materials should be addressed to Z.L. (email: mailto:[email protected]

Web End [email protected] ) or to H.P. (email: mailto:[email protected]

Web End [email protected] ) or toY.C. (email: mailto:[email protected]

Web End [email protected] ).

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The unique Dirac-cone band structure makes graphene a promising material for photodetection. Its linearly dispersive band structure near Fermi level results in

massless Dirac fermion type of carriers, large Fermi velocity (B1/300 of the speed of light) and surprisingly high carrier mobility14. In graphene device, the photovoltage generation time is shorter than 50 fs, which is associated with the carrier heating time5. In addition, the rapid cooling process of photoexcited carriers (Bpicoseconds) in the monolayer graphene results in a quick annihilation of photoelectrical signal in the electric circuit512. These advantages of the monolayer graphene facilitate its applications associated with ultrafast photodetection, such as high-speed optical communications1317 and terahertz oscillators18. However, it remains a great challenge to achieve high photoresponsivity and selectivity in the monolayergraphene-based detectors due to the weak and broadband absorption (only 2.3%, from the ultraviolet to the infrared)19 and the short photocarrier cooling time (Bpicoseconds)512.

On the other hand, twisted bilayer graphene (tBLG) is non-AB stacked bilayer graphene in which one graphene monolayer sheet rotates by a certain angle (y) relative to the other (Fig. 1a). Recent theoretical studies of tBLG have shown that the Dirac band dispersions change dramatically and become strongly warped with small twist angles (yr5)2023. Even at relatively large twist angles, the electronic coupling between the two monolayers, albeit weak, can still introduce new band structures2027. Unlike the parabolic band structure in AB-stacked bilayer graphene2834, the band structure of tBLG with large twist angle (typically larger than 5)20,35 maintains linear near the Dirac point and thus it inherits some unique properties of monolayer graphene36. Away from the Dirac point, Dirac cones of the two individual

monolayers intersect and form saddle points in reciprocal space of tBLG24, leading to the formation of van Hove singularities (VHSs) in the density of state (DOS)25,26,35,37,38, which then gives rise to some interesting phenomena such as enhanced optical absorption, Raman G-band resonance and enhanced chemical reactivity of tBLG27,37,3945.

In this study, to address the problem of low photoresponsivity and selectivity in the monolayer graphene photodetection, we explore the high-performance photodetector based on tBLG with VHSs. For the rst time, we report that the VHSs in tBLG leads to a prominent photocurrent enhancement of tBLG photodetectors with a wavelength selectivity under incident light irradiation.

ResultsStructure and Raman spectra. tBLG samples were grown on copper foil via chemical vapour deposition (CVD) method and then transferred to heavily doped Si substrate, which was capped with 90 nm SiO2. As shown in typical optical image and scanning electron microscopy images (Fig. 1b,c), both the overlayer and underlayer in tBLG exhibit hexagonal shapes with sharp edges, which implies highly crystalline qualities of tBLG domains4648. The interlayer twist angle can be measured from the relative misalignment of the straight edges, which is consistent with the observation by transmission electron microscopy (TEM) (Supplementary Fig. 1 and Supplementary Note 1). tBLG domains with different twist angles can be readily obtained in our samples (Fig. 1d), which provide a platform for the study of y-dependent lightmatter interactions. The highly crystalline quality and clean interface between two monolayers of our CVD sample are evidenced by the moir pattern in high-resolution

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Figure 1 | Structures and Raman spectra of tBLG with different twist angles. (a) Schematics for band structure with minigaps (top left) and the corresponding DOS with VHSs (top right) in tBLG (bottom). Blue arrows describe the photoexcitation process as the energy interval of two VHSs (2EVHS)

matches the energy of incident photon. (b) The optical image of tBLG domains grown by CVD on Cu and then transferred onto SiO2 (90 nm)/Si substrate. Scale bar, 30 mm. (c) Scanning electron microscopy (SEM) images of tBLG domains with different twist angles on SiO2/Si. The twist angles are measured from the edges of over- and underlayer of tBLG domains. Scale bars, 5 mm. (d) Histogram of twist angles measured from tBLG domains in the CVD sample as shown in b. (e) Typical high-resolution TEM (HRTEM) image of tBLG. The periodicity of the moir pattern is B0.455 nm. The inset is the fast Fourier transform (FFT) of the image, showing that the twist angle is 29. Scale bar, 2 mm. (f) Left column, Raman spectra of monolayer graphene and tBLG domains with twist angle of 5, 8, 10.5, 13, 16 and 29, respectively. The incident laser wavelength is 532 nm (2.33 eV). Top right: the optical image of 13 tBLG domain on SiO2/Si. Bottom right: G-band intensity mapping image of the 13 tBLG domain shows uniformity of the intensity enhancement of

Raman G-band. Scale bars, 10 mm.

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TEM image (Fig. 1e). This clean interface guarantees the interaction and coupling of electronic states from the over- and underlayer of tBLG. This interlayer electronic coupling is also proved by the enhanced G-band peak in Raman spectra (Fig. 1f). Taking 13 tBLG domain as an example, the Raman G-band intensity displays a tremendous enhancement of B20 folds under 532 nm laser (2.33 eV), which is consistent with the previously reported results27,28,3943. This Raman G-band enhancement implies that an interlayer coupling introduces new band structures in tBLG. In addition, the enhanced G-band intensity of 13 tBLG domain was found to be uniform across the whole domain as shown in the G-band mapping image (Fig. 1f), which further conrms the high quality of our CVD tBLG samples. The Raman G-band enhancement is believed to correlate with the formation of VHSs in tBLG27,37,3942,49.

Micro-ARPES spectra of tBLG. To unravel the nature of VHSs, we directly investigate the band structures of CVD-grown tBLG domains using spatially resolved angle-resolved photoemission spectroscopy with submicrometre spatial resolution (micro-ARPES). Owing to the twist angle (y) between over- and underlayer of tBLG, the two sets of (six) Dirac points originated from each layer are rotated relatively by the angle y as well (see Fig. 2a), which we mark as the k (left cones) and ky (right cones) points, respectively. The band structures of a tBLG domain are shown in Fig. 2, where the constant energy contours (Fig. 2b), the band dispersions cutting across (Fig. 2c) and perpendicular (Fig. 2d) to the two adjacent Dirac points are presented, respectively. In Fig. 2b, the stacking plots of the band contours at different binding energies clearly depict the typical two Dirac-cone dispersions of tBLG and each preserves the linear dispersion of monolayer graphene. One of the Dirac cone exhibits a weaker intensity and higher electron doping level, indicating its origin from the underlayer graphene, as the photoelectrons from the bottom layer are screened by the top layer (thus leading to a weaker intensity), and being closer to the Cu substrate also increases its charge transfer50,51.

By measuring the separation between the two Dirac points (Fig. 2b,c), we can determine the twist angle (y) of this tBLG domain as 19.1 (Supplementary Fig. 2 and Supplementary Note2). Without interlayer coupling, the two Dirac cones in Fig. 2 shall intersect and cross each other at higher binding energy. Instead, the band structure at Fig. 2b clearly shows ne structures at the intersection (indicated by red arrows in Fig. 2b) and the dispersion in Fig. 2c shows the opening of the gap at the crossing point of the dispersions from the two Dirac cones, which is indicated by the faint intensity in the spectra intensity map (left panel) and the dip in the DOS plot (right panel, indicated by red arrows). This gap opening in the band structure is a typical anticrossing behaviour introduced by interlayer electronic coupling24, which leads to the formation of the VHS (Fig. 1a). In addition, from Fig. 2d, one can see that the anticrossing affects the hyperbolic curve as well and results in split and parallel dispersions.

With the same method, we further studied tBLG domains with various different twist angles and tracked the positions of VHSs with respect to the twist angles, as can be seen in Fig. 2e. At small angles, the value of EVHS increases almost linearly with y, in consistence with the theoretical prediction (Supplementary Fig. 2). This dependence also helps explain the Raman G-band enhancement at specic twist angle (Fig. 1f) for a given incident laser frequency. If the energy of incident photon matches the energy interval of the two VHSs of tBLG (_oE2EVHS, see

Fig. 1a), the electrons are excited and transit between the ne band structure, causing the increase of the intensity of Raman G

band peak (see Supplementary Fig. 3 and Supplementary Note 3 for details).

Selectively enhanced photocurrent generation of tBLG. The strong lightmatter interaction of tBLG selectively enhanced by the VHSs can also enhance the generation of photocurrent under illumination. As an example, two adjacent tBLG domains with twist angle of 13 and 7 transferred onto SiO2 (90 nm)/Si were etched into a strip and then embedded into two-terminal devices in parallel (Fig. 3a,b). Raman spectroscopy and two-dimensional maps of the two adjacent tBLG domains were rst measured under the 532-nm laser (2.33 eV). As expected, the G-band intensity of whole 13 domain exhibits a uniformly 20-fold enhancement as compared with the 7 domain (see Fig. 3c), as the energy interval of the two VHSs in 13 domain matches the energy of incident photon (_oE2EVHS). To generate

photocurrent selectively, interfacial junctions of tBLG-metal electrodes were used to separate the photoexcited electrons and holes under illumination52,53. As shown in currentbias voltage curves, both tBLG domains produce pronounced photocurrent

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Figure 2 | Micro-ARPES spectra of tBLG. (a) Schematic illustration of the rst primitive Brillouin zones (hexagons) and Dirac cones of over- and underlayer of tBLG. (b) Stacking plot of constant-energy contours at different binding energies (EB) of tBLG. (c) ARPES spectra along Cut 1 as labelled in a. The right curve is energy spectrum density curve (EDC) integrated from the spectrum. (d) ARPES spectra along Cut 2 as labelled in a. Red arrows in b,c and d indicate the minigap band topology and the split parallel branches arising from interlayer coupling. (e) EVHS versus the twist angle (y) of tBLG domains. The EVHS, measured from micro-ARPES data of tBLG, is the energy interval between the minigap (VHS) and Dirac point.

The EVHS varies almost linearly with twist angle. The black dashed line is a theoretical curve.

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Figure 3 | Selectively enhanced photocurrent generation in tBLG photodetection devices. (a) Schematic illustration of a tBLG photodetection device. The channel comprises of two adjacent tBLG domains with different twist angles of y1 and y2, respectively. (b) Optical image of the tBLG photodetection device.

The y1 and y2 are 7 and 13, respectively. (c) Raman G-band intensity mapping image under 532 nm (2.33 eV) laser. 13 tBLG domain exhibits an enhanced G-band intensity. (d) Current versus source-drain bias (IV) curve without laser on and with laser focusing on 7 (spot A) and 13 (spot B) tBLG domains, respectively. The intercepts at current axis represent the net photocurrents. (e) Scanning photocurrent images of the same tBLG device. A 532-nm laser with power of 200 mW is focused on the device, while the net photocurrent is amplied and then detected by a lock-in amplier. All the photocurrents here are generated without source-drain bias and gate bias. (f) Three-dimensional view of the scanning photocurrent image of the same tBLG device.

(g) Photocurrents generated from 7 (spot A) and 13 (spot B) tBLG domains as a function of incident power, respectively. The white dashed lines in c and e show the positions of graphenemetal electrode interfaces, respectively. Scale bars, 5 mm (all).

shifts (Fig. 3d). Remarkably, the 13 tBLG domain generates a much larger net photocurrent (0.63 mA) at zero bias than that of the 7 domain (0.097 mA), originated from selectively enhanced lightmatter interaction of 13 tBLG domain with the 532-nm laser.

We further conducted net photocurrent mapping of the device by using scanning photocurrent microscopy, in which the net photocurrent was recorded while scanning a focused 532-nm laser spot with a diameter of B1 mm over the device (Fig. 3e,f).

The photocurrent was observed to exhibit contrary directions at the two graphenemetal electrode interfaces in the device. Signicantly, the intensity of photocurrent generated at 13 tBLG domain is B6.6 times stronger than that at the 7 tBLG domain.

This twist angle-related photocurrent enhancement holds great promise in high-selectivity photodetection applications.

To further evaluate the photoresponsivity of tBLG, we performed photocurrent measurements of tBLG devices under different incident power of 532 nm laser illumination, respectively. As shown in Fig. 3g, the photocurrents from 7 and 13 tBLG domains both increase as the incident power rises from

B1 mW to B5 mW. The photoresponsivity of 7 and 13 tBLG domain is measured as B0.15 and B1 mA W 1, respectively, indicating a robust and strong enhancement in 13 tBLG domain under different incident power of 532 nm laser illumination.

From the unravelling of band structures, the energy interval of the two VHSs (2EVHS) of 13 tBLG domain is B2.34 eV, which matches the energy of incident photon (2.33 eV, l 532 nm) and

thus leads to a strong lightmatter interaction. When we changed the wavelength of incident laser from 532 to 632.8 nm (1.96 eV),

the photocurrent was found to be selectively enhanced in a 10.5 tBLG domain device with 2EVHS of B1.89 eV (Supplementary

Fig. 4 and Supplementary Note 4). To further investigate the correlation of 2EVHS with _o in photocurrent generation of 13

and 10.5 tBLG domains, _o was gradually changed from 1.77 to2.48 eV (500 to 700 nm in wavelength), while the power of incident laser was kept unchanged. As shown in Fig. 4a, the photocurrents of 13 and 10.5 tBLG domains exhibit peaks at B2.30 and B1.94 eV, agreeing well with 2EVHS values (B2.34 and B1.89 eV), respectively.

DiscussionThe origin of the photocurrent enhancement can be understood qualitatively when taking the unique electronic state of tBLG into account. In the photoexcitation process, the interband transition has to satisfy both momentum and energy conservation. For momentum conservation, the electrons are conned to transit between states with the same k value in reciprocal space, owing to the very small momentum of incident photons. As for energy conservation, the energy difference between these two states equals to _o. When _oE2EVHS, the initial and nal states are both near VHSs (thus with enhanced DOS, see Fig. 1a). Specically, the effect of VHSs on the photoexcitation process can be evaluated by joint DOS (JDOS), which is dened as:

JDOSo

1 4p3

Z d Ec k

Ev k

_o

dk 1

where EC and EV represent the energies of the conduction and

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valence bands, respectively. JDOS is associated with the process in

which an electron absorbs a photon with energy _o Ec Ev and

then transits from conduction to valence band. A calculated JDOS shows an abrupt increase associated with the VHSs when _oE2EVHS (ref. 40). This leads to an enhanced photo-excitation process, consistent with experimental observations in Raman (Fig. 1f) and absorption spectra27,45. As a result, the intensied photoexcitation process may result in the enhanced photocurrent generation.

Besides the efcient photoexcitation, the improvement of separation efciency of excited carriers can facilitate the photocurrent generation in tBLG. A gate voltage applied on the tBLG photodetection device can manipulate the doping level of

graphene in channel and thus change the value of Seebeck coefcient, which may simultaneously lead to the photocurrent change5457. As shown in Fig. 4b, the photocurrent of 13 tBLG domain has a 2.6-fold increase from B25 to B66 nA when the back-gate voltage decreases from 0 to 20 V. As the back-gate

voltage increases from 0 to 20 V, the photocurrent rst ips its polarity at 2.5 V and then reaches a value of about 82 nA. The

inset in Fig. 4b shows the two band proles of graphene metal electrode junctions in the tBLG photodetection device under the applied back-gate voltage. From the transfer curve (Supplementary Fig. 5 and Supplementary Note 5), we believe that the positive gate voltage manipulates the graphene in channel from p- to n-type doping, which gives rise to the change of Seebeck coefcient. In contrast, owing to the Fermi-level pinning of graphene underneath the metal electrodes, its Seebeck coefcient keeps unchanged. Therefore, the difference of these two Seebeck coefcients could be tuned and ipped by gate voltage, which leads to the value and polarity change of photocurrent.

The responsivity of tBLG is measured as B1 mA W 1 at the resonance frequency, which is about 20 times enhancement compared with that of mechanically exfoliated monolayer graphene (B0.05 mA W 1) with similar device conguration (Supplementary Fig. 6). To further improve the responsivity, we have integrated tBLG with plasmonic electrode structures as shown in Fig. 5a. A tBLG domain and an adjacent monolayer domain were embedded into the same two-terminal electrodes. A nger-patterned plasmonic structure (Ti/Au, 5/45 nm in thickness) with 110 nm nger width and 300 nm pitch58 were fabricated on the tBLG domain as shown in Fig. 5b,c. The Raman mapping image in Fig. 5d exhibits uniformly enhanced G-band intensity, which conrms that the interval of two VHSs (2EVHS)

of the tBLG domain matches the energy of incident photon (532 nm and 2.33 eV). The scanning photocurrent results of the device (Fig. 5e,f) show that the photocurrents of tBLG and the adjacent monolayer domain are measured as B10 and B0.95 nA,

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Figure 4 | The variation of photocurrent with photon energy and gate voltage. (a) Photocurrent versus energy of incident photon (_o). tBLG domains with 10.5 and 13 twist angles show different peak positions. Incident photons with energy o near 2EVHS generate an enhanced photocurrent, while photons with energy lower or higher than 2EVHS excite

ordinary optoelectronic processes. Dotted lines were used to guide the eyes. The plots are normalized with that of AB-stacked bilayer graphene. (b) Plot of photocurrent as function of gate voltage. Insets are the corresponding band proles, where the grey boxes, blue dotted lines and black dotted lines represent Ti electrodes, Fermi levels and positions of Dirac points of tBLG, respectively.

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Figure 5 | tBLG photodetector integrated with plasmonic structure. (a) Schematic illustration of the detector. The channel comprises graphene monolayer domain and tBLG domain which are labelled by 1L and 2L, respectively. The electrode is integrated with nger structure. (b) Optical image of the tBLG photodetector. (c) Scanning electron microscopy (SEM) image of the nger structure labelled by black dashed rectangle in b. (d) Raman G-band intensity mapping image of the device under 532 nm laser. The tBLG domain exhibits an enhanced G-band intensity. (e) Scanning photocurrent image of the photodetector. The exciting light is a focused 532 nm laser with power of 30 mW. (f) Line-scanning photocurrent of the photodetector. The blue, red and black curves correspond to photocurrent distributions along the tBLG near gure structure, tBLG and graphene monolayer, which are labelled by blue, red and black dashed lines in e. The maximum photocurrent at tBLG with the plasmonic structure is 77 nA, while the maximum photocurrents at the tBLG and monolayer graphene are 10 and 0.95 nA, respectively. All the photocurrents here are generated without source-drain bias and gate bias. The red dashed rectangles in b,d and e correspond to the channel of the photodetector. Scale bar, 1 mm (nger structure in c). Scale bars, 5 mm (others).

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respectively. The enhancement of about 10.5 times is achieved. Remarkably, the photocurrent generated on tBLG near the nger structure is further enhanced to the value of B77 nA, which is B80-fold enhancement compared with the photocurrent of adjacent monolayer graphene channel. The mechanism of such strong photoresponsivity enhancements can be ascribed to the combination of the selective resonance enhancement of VHSs in tBLG and plasmonic enhancement of the nger structure.

In summary, we have experimentally demonstrated that the lightmatter interaction in tBLG with VHSs is dependent on the interlayer twist angle (y) and then can lead to a selective enhancement in photocurrent generation. Micro-ARPES was performed to unravel the band structure of CVD-grown tBLG and reveal the emergence of y-dependent VHSs. The photo-current of tBLG photodetectors exhibits a B6.6-fold enhancement at a suitable y, when the energy interval of the VHSs (2EVHS) matches the energy of incident photon (_o). By integrating plasmonic structures, the responsivity of tBLG photodetector can be signicantly enhanced by B80 folds compared with the monolayer graphene. Our results open a new route to graphene-based optoelectronic applications.

Methods

tBLG growth and characterization. The tBLG was grown on copper foil in a home-made low-pressure CVD system. The growth was carried out under the ow of H2 and CH4 (600:1 in volume) with a pressure of 600 Pa at 1,030 C for 40 min.

The samples were characterized by Olympus BX51 microscope, scanning electron microscopy (Hitachi S-4800 operated at 2 kV), TEM (FEI Tecnai F30 operated at 300 kV for the diffraction image and FEI 80-300 Cs image-corrected Titan operated at 80 kV for the moir pattern image) and Raman spectroscopy (Horiba HR800). The micro-ARPES measurements were carried out at the spectromicroscopy beamline at Elettra Synchrotron Radiation lab in Italy, with energy resolutionof 50 meV, spatial resolution of 0.8 mm and angle resolution of 0.5. Before the micro-ARPES measurements, in-situ annealing at 350 C was carried out to clean the sample surface.

Device fabrication and measurement. tBLG samples on copper were transferred to a highly doped Si substrate with 90 nm SiO2 with the help of poly(methyl methacrylate)59. The Ti/Au (20/30 nm) electrodes and Ti/Au (5/45 nm) gure structures were fabricated by electron-beam lithography and the following electron-beam evaporation. The electrical measurements were performed by Keithley SCS-4200. The photoelectrical measurements were performed by a scanning photocurrent microscopy. In the set-up, 532 and 632.8 nm, and Supercontinuum Laser Sources (NKT Photonic) were used as laser sources. The chopper-modulated (B1 kHz) laser beams were focused to B1 mm on the device using 100 objective and the short-circuit photocurrents were then measured by

pre-amplier and lock-in amplier. When scanning the laser spot over the device, the induced photocurrents and beam positions were recorded and displayed simultaneously with the assistance of a computer, which communicated with lock-in amplier and motorized stage (with device on it). A voltage source (Keithley 2400) was used to supply the gate voltage. All the electrical and photoelectrical measurements were performed in air at room temperature.

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Acknowledgements

We are grateful to Dr Yao Guo and Mr Chen Peng from Department of Electronics, Peking University, for their suggestions in device fabrication, and Mr Ziwei Li from School of Physics, Peking University, for the calculation regarding to plasmonic structures. We acknowledge nancial support from the National Basic Research Program of

China (numbers 2014CB932500, 2011CB921904 and 2013CB932603), the National Natural Science Foundation of China (numbers 21173004, 21222303, 51121091 and 51362029), the National Program for Support of Top-Notch Young Professionals and Beijing Municipal Science and Technology Commission (Z131100003213016). Part of this work was performed at the Stanford Nano Shared Facilities.

Author contributions

J.Y. and H.L.P. conceived and designed the experiments. J.Y and H.W. performed the synthesis and structural characterization. J.Y. made the devices and carried out optoelectronic measurements. Z.T., L. Liao, L. Lin and X.S. assisted in experimental work and contributed to the scientic discussions. H.P. and Y.L.C. preformed micro-ARPES. A.L.K. and H.L.P. conducted the TEM, high-resolution TEM and aberration-corrected high-resolution TEM experiments. J.Y., H.L.P. and H.P. wrote the paper. H.L.P., Z.L. and Y.L.C. supervised the project. All the authors discussed the results and commented on the manuscript.

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How to cite this article: Yin, J. et al. Selectively enhanced photocurrent generation in twisted bilayer graphene with van Hove singularity. Nat. Commun. 7:10699doi: 10.1038/ncomms10699 (2016).

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