$^{13}$CO molecules are intercalated under a single layer graphene film on Ru(0001) and interrogated with helium low energy ion scattering. Single scattering is used to determine the mass distribution of atomic species visible to the ion beam and detector, and the scattering angle is varied to distinguish adsorbed from intercalated molecules. At room temperature, CO intercalates as molecules that sit upright with the O end on top, as on clean Ru. The intercalated CO tilts, more than it does on clean Ru, when the temperature is raised. This is presumably due to increased vibrational amplitudes combined with the confining effect of the graphene film.
Intercalation of rare earth metals ($RE$ = Eu, Dy, and Gd) is achieved by depositing the $RE$ metal on graphene that is grown on silicon-carbide (SiC) and by subsequent annealing at high temperatures to promote intercalation. STM images of the films reveal that the graphene layer is defect free and that each of the intercalated metals has a distinct nucleation pattern. Intercalated Eu forms nano-clusters that are situated on the vertices of a Moir{è} pattern, while Dy and Gd form randomly distributed nano-clusters. X-ray magnetic circular dichroism (XMCD) measurements of intercalated films rev…
We demonstrate a new method to control the Fermi level around the van Hove singularity (VHS) in Li-intercalated graphene on the SiC substrate. By angle-resolved photoemission spectroscopy, we observed a clear Lifshitz transition in the vicinity of the VHS by increasing the graphene thickness. This behavior is unexpected in a free-standing Li-intercalated graphene model. The calculation including the substrate suggests that the surface state stabilizes the Fermi level around the VHS of the Dirac bands via hybridization. In addition, we found that a sizable Schottky barrier is formed between gra…
X-ray magnetic circular dichroism (XMCD) reveal the magnetic properties of intercalated europium metal under graphene on SiC(0001). Intercalation of Eu nano-clusters (average size 2.5 nm) between graphene and SiC substate are formed by deposition of Eu on epitaxially grown graphene that is subsequently annealed at various temperatures while keeping the integrity of the graphene layer. Using sum-rules analysis of the XMCD of Eu M$_{4,5}$ edges at $T = 15$ K, our samples show paramagnetic-like behavior with distinct anomaly at T $\approx$ 90 K which may be related to the N{è}el transition, T$_N$…
Here we report on a "new" type of ordering which allows to modify the electronic structure of a graphene monolayer (ML). We have intercalated small gold clusters between the top monolayer graphene and the buffer layer of epitaxial graphene. We show that these clusters perturb the quasiparticles on the ML graphene, and act as quantum dots creating a superlattice of resonators on the graphene ML, as revealed by a strong pattern of standing waves. A detailed analysis of the standing wave patterns using Fourier Transform Scanning Tunneling Spectroscopy strongly indicates that this phenomenon can a…
Doping graphene near the 1/4 filling to shift the extended flat band and van Hove singularity below E$_F$ has been highly desirable. Here we report the experimental observation of an extended flat band below E$_F$ in Li-intercalated graphene. Strong electron-phonon interaction is clearly identified by notable kinks in the band dispersion. Moreover, the evolution of the band structure upon Li intercalation shows that the extended flat band and the Kekulé order emerge simultaneously. Our work provides opportunities for investigating flat band related instabilities and its interplay with the Keku…
Ultrafast carrier dynamics of pristine bilayer graphene (BLG) and bilayer graphene intercalated with FeCl3 (FeCl3-G), were studied using time-resolved transient differential reflection (delta R/R). Compared to BLG, the FeCl3-G data showed an opposite sign of delta R/R, a slower rise time, and a single (instead of double) exponential relaxation. We attribute these differences in dynamics to the down-shifting of the Fermi level in FeCl3-G, as well as the formation of numerous horizontal bands arising from the d-orbitals of Fe. Our work shows that intercalation can dramatically change the electro…
The diffusive motion of metal nanoparticles Au and Ag on monolayer and between bilayer heterostructures of transition metal dichalcogenides and graphene are investigated in the framework of density functional theory. We found that the minimum energy barriers for diffusion and the possibility of cluster formation depend strongly on both the type of nanoparticle and the type of monolayers and bilayers. Moreover, the tendency to form clusters of Ag and Au can be tuned by creating various bilayers. Tunability of the diffusion characteristics of adatoms in van der Waals heterostructures holds promi…
Understanding the interactions of ambient molecules with graphene and adjacent dielectrics is of fundamental importance for a range of graphene-based devices, particularly sensors, where such interactions could influence the operation of the device. It is well-known that water can be trapped underneath graphene and its host substrate, however, the electrical effect of water beneath graphene and the dynamics of how it changes with different ambient conditions has not been quantified. Here, using a metal-oxide-graphene variable-capacitor (varactor) structure, we show that graphene can be used to…
We use angle-resolved photoemission spectroscopy to investigate the electronic structure of bilayer graphene at high n-doping and extreme displacement fields, created by intercalating epitaxial monolayer graphene on silicon carbide with magnesium to form quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide. Angle-resolved photoemission spectroscopy reveals that upon magnesium intercalation, the single massless Dirac band of epitaxial monolayer graphene is transformed into the characteristic massive double-band Dirac spectrum of quasi-freestanding bilayer graphene. Analys…
Intercalation of Au can produce giant Rashba-type spin-orbit splittings in graphene but this has not yet been achieved on a semiconductor substrate. For graphene/SiC(0001), Au intercalation yields two phases with different doping. Here, we report the preparation of an almost pure p-type graphene phase after Au intercalation. We observe a 100 meV Rashba-type spin-orbit splitting at 0.9 eV binding energy. We show that this giant splitting is due to hybridization and much more limited in energy and momentum space than for Au-intercalated graphene on Ni.
Electrode-tunable nonlocal charge to spin conversion in WSe$_2$-intercalated bilayer graphene
Institute of Informatics, Slovak Academy of Sciences（斯洛伐克科学院信息学研究所）；Faculty of Physics, University of Belgrade（贝尔格莱德大学物理学院）；Institute of Physics, Pavol Jozef Šafárik University in Košice（科希策帕维尔·约瑟夫·沙法里克大学物理研究所）；Institute of Experimental Physics, Slovak Academy of Sciences（斯洛伐克科学院实验物理研究所）；New Technologies Research Centre, University of West Bohemia（西波希米亚大学新技术研究中心）
Recent observation of proximity effect \cite{Morpurgo:2007} has ignited interest in superconductivity in graphene and its derivatives. We consider Ca-intercalated graphene bilayer and argue that it is a superconductor, and likely with a sizeable $T_{c}$. We find substantial and suggestive similarities between Ca-intercalated bilayer (C$_{6}$CaC$_{6}$), and CaC$_{6} $, an established superconductor with $T_{c}$ = 11.5 K. In particular, the nearly free electron band, proven to be instrumental for superconductivity in intercalated graphites, does cross the chemical potential in (C$_{6}$CaC$% _{6}…
The interlayer gallery between two adjacent sheets of van der Waals materials is expected to modify properties of atoms and molecules confined at the atomic interfaces. Here, we directly image individual hydrogen atom intercalated between two graphene sheets and investigate its dynamics by scanning tunnelling microscope (STM). The intercalated hydrogen atom is found to be remarkably different from atomic hydrogen chemisorbed on external surface of graphene. Our STM measurements, complemented by first-principles calculations, show that the hydrogen atom intercalated between two graphene sheets …
We have performed an \it {ab initio} investigation of transition metals (TMs = Mo, Ru, Co, and Pt) embedded in twisted bilayer graphene (tBG) layers. Our total energy results reveal that, triggered by the misalignment between the graphene layers, Mo and Ru atoms may form a quasi-periodic (triangular) array of intercalated atoms. In contrast, the formation of those structures is not expected for the other TMs, Co and Pt atoms. The net magnetic moment (m) of Mo and Ru atoms may be quenched upon intercalation, depending on the stacking region (AA or AB). For instance, we find a magnetic moment of…
Graphene intercalation materials are potentially promising for the implementation of the ultra-low power, excitonic-condensate-based Bilayer pseudoSpin Field-Effect Transistor (BiSFET) concept, as well as other novel device concepts requiring a graphene interlayer dielectric. Using density functional theory (DFT) we study the structural and electronic properties of bilayer graphene intercalated with iodine monochloride (ICl) and iodine monobromide (IBr). We determine the structural configuration of ICl and IBr graphene intercalation compounds (GICs). We also conduct an in-depth exploration of …
Functional manipulation of graphene is an important topic in view of both fundamental researches and practical applications. In this study, we show that intercalation of 5$d$ transition metals in epitaxial graphene on SiC is a promising approach to realize topologically nontrivial phases with a finite band gap in graphene. Using first-principles calculations based on density functional theory, we show that the Re- and Ta-intercalated graphene become two-dimensional topological insulators which exhibit linear Dirac cones and quadratic bands with topological band gaps, respectively. The appearan…
Point defects and their dynamic behaviors in silver monolayer intercalated between graphene and SiC
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e. V.（柏林莱布尼茨固体电子学保罗·德鲁德研究所）；Department of Materials Science and Engineering, The Pennsylvania State University（宾夕法尼亚州立大学材料科学与工程系）；Dimensional Crystal Consortium, The Pennsylvania State University（宾夕法尼亚州立大学二维晶体联盟）；Center for 2-Dimensional and Layered Materials, The Pennsylvania State University（宾夕法尼亚州立大学二维与层状材料中心）；Center for Atomically Thin Multifunctional Coatings, The Pennsylvania State University（宾夕法尼亚州立大学原子级薄多功能涂层中心）
Our first-principles calculations show that an energy gap around 0.12-0.25 eV can be engineered in epitaxial graphene on SiC(0001) through the non-covalent intercalation of transition- or alkali-metals, yet originated from the distinct mechanisms. The former is attributed to the combined effects of metal induced perpendicular electric field and interaction while the latter is solely attributed to the built-in electric field. A great advantage of this scheme is that the gap size is almost independent of the gate voltage up to 1 V/nm, thus reserving the electric means to tune the Fermi level of …
Among two-dimensional atomic crystals, hexagonal boron nitride (hBN) is one of the most remarkable materials to fabricate heterostructures revealing unusual properties. We perform first-principles calculations to determine whether intercalated metal atoms and vacancies can mediate interfacial coupling and influence the structural and electronic properties of the graphene/hBN heterostructure. Metal impurity atoms (Li, K, Cr, Mn, Co, and Cu) as extrinsic defects between the graphene and hBN sheets produce $n$-doped graphene. We also consider intrinsic vacancy defects and find that a boron monova…
Ca-intercalation has opened a way for superconductivity in graphene on SiC. However, the atomic and electronic structures being critical for superconductivity are still under discussion. We find the essential role of the interface between monolayer graphene and the SiC substrate for superconductivity. In the Ca-intercalation process, at the interface a carbon layer terminating SiC changes to graphene by Ca-termination of SiC (monolayer graphene becomes bilayer) with inducing more carriers than a free-standing model. Then, Ca is intercalated in-between graphene layers, which shows superconducti…
We investigate the structure, chemical bonding, electronic properties, and magnetic behavior of a three-dimensional graphitic network in aba and aaa stacking with intercalated transition metal atoms (Mn, Fe, Co, Ni, and Cu). Using density functional theory, we find induced spin-polarization of the C atoms both when the graphene sheets are aba stacked (forming graphite) and aaa stacked (resembling bi-layer graphene). The magnetic moment induced by Mn, Fe, and Co turns out to vary from 1.38 μB to 4.10 μB, whereas intercalation of Ni and Cu does not lead to a magnetic state. The selective inducti…
An iterative method bridging DFT, disorder averaging, and experiment in intercalated materials: application to Au-intercalated graphene
Université Paris Saclay（巴黎萨克雷大学）；CNRS（法国国家科学研究中心）；CEA（法国原子能和替代能源委员会）；Institut de Physique Théorique（理论物理研究所）；Laboratoire de Physique des Solides（固体物理实验室）；Instituto de Física, Universidade Federal de Goiás（戈亚斯联邦大学物理研究所）；Aix Marseille Univ（艾克斯-马赛大学）；Université de Toulon（土伦大学）；CPT（凝聚态物理中心）；Institut de Sciences des Matériaux de Mulhouse（米卢斯材料科学研究院）；CNRS-UMR 7361 Université de Haute Alsace（上阿尔萨斯大学）
It is generally believed that the inter-edge coupling destroys the quantum spin Hall (QSH) effect along with the gap opening at the Dirac points. Using first-principles calculations, we find that the quantized edge transport persists in the presence of inter-edge coupling in Ta intercalated epitaxial graphene on SiC(0001), being a QSH insulator with the non-trivial gap of 81 meV. In this case, the band is characterized by two perfect Dirac cones with different Fermi velocities, yet only one maintains the edge state feature. We attribute such an anomalous behavior to the orbital-dependent decay…
Graphene is a fascinating 2D material that is being widely investigated for use in electronic devices due to its unique electronic and materials properties. Also, because of its high thermal stability and inertness, it is considered a promising candidate for use as a protection layer for metal substrates. Here, graphene films grown on Ru(0001) are held at 600 K while reacted with oxygen (O$_2$) and then investigated with helium low energy ion scattering (LEIS). LEIS spectra collected at different scattering angles confirm that oxygen does not adsorb to graphene, but instead intercalates betwee…
We perform a femtosecond-THz optical pump-probe spectroscopy to investigate the cooling dynamics of hot carriers in quasi-free standing bilayer epitaxial graphene. We observed longer decay time constants, in the range of 2.6 to 6.4 ps, compared to previous studies on monolayer graphene, which increase nonlinearly with excitation intensity. The increased relaxation times are due to the decoupling of the graphene layer from the SiC substrate after hydrogen intercalation which increases the distance between graphene and substrate. Furthermore, our measurements do not show that the supercollision …
Graphene holds promises for exploring exotic superconductivity with Dirac-like fermions. Making graphene a superconductor at large scales is however a long-lasting challenge. A possible solution relies on epitaxially-grown graphene, using a superconducting substrate. Such substrates are scarce, and usually destroy the Dirac character of the electronic band structure. Using electron diffraction (reflection high-energy, and low-energy), scanning tunneling microscopy and spectroscopy, atomic force microscopy, angle-resolved photoemission spectroscopy, Raman spectroscopy, and density functional th…
A suspended layer made up of ferromagnetically ordered spins could be created between two mono/multilayer graphene through intercalation. Stability and electronic structure studies show that, when fluorine molecules are intercalated between two mono/multilayer graphene, their bonds get stretched enough ($\sim$ 1.9$-$2.0 Å) to weaken their molecular singlet eigenstate. Geometrically, these stretched molecules form a pseudoatomized fluorine layer by maintaining a van der Waals separation of $\sim$ 2.6 Å from the adjacent carbon layers. As there is a significant charge transfer from the adjacent …
Intercalation is an established technique for tailoring the electronic structure of epitaxial graphene. Moreover, it enables the synthesis of otherwise unstable two-dimensional (2D) layers of elements with unique physical properties compared to their bulk versions due to interfacial quantum confinement. In this work, we present uniformly Pb-intercalated quasi-freestanding monolayer graphene on SiC, which turns out to be essentially charge neutral with an unprecedented $p$-type carrier density of only $(5.5\pm2.5)\times10^9$ cm$^{-2}$. Probing the low-energy electronic structure throughout the …
Metal-intercalated graphene on Ir(111) exhibits phonon signatures in inelastic elec- tron tunneling spectroscopy with strengths that depend on the intercalant. Extraor- dinarily strong graphene phonon signals are observed for Cs intercalation. Li interca- lation likewise induces clearly discriminable phonon signatures, albeit less pronounced than observed for Cs. The signal can be finely tuned by the alkali metal coverage and gradually disappears upon increasing the junction conductance from tunneling to con- tact ranges. In contrast to Cs and Li, for Ni-intercalated graphene the phonon signal…
The interband pi and pi+sigma plasmons in pristine graphene and the Dirac plasmon in doped graphene are not applicable, since they are broad or weak, and weakly couple to an external longitudinal or electromagnetic probe. Therefore, the ab initio Density Function Theory is used to demonstrate that the chemical doping of the graphene by the alkali or alkaline earth atoms dramatically changes the poor graphene excitation spectrum in the ultra-violet frequency range (4 - 10 eV). Four prominent modes are detected. Two of them are the intra-layer plasmons with the square-root dispersion, characteri…
We present a systematical study via scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) on the effect of the exposure of Lithium (Li) on graphene on silicon carbide (SiC). We have investigated Li deposition both on epitaxial monolayer graphene and on buffer layer surfaces on the Si-face of SiC. At room temperature, Li immediately intercalates at the interface between the SiC substrate and the buffer layer and transforms the buffer layer into a quasi-free-standing graphene. This conclusion is substantiated by LEED and STM evidence. We show that intercalation occurs th…
The prospect of a Dirac half metal, a material which is characterized by a bandstructure with a gap in one spin channel but a Dirac cone in the other, is of both fundamental interest and a natural candidate for use in spin-polarized current applications. However, while the possibility of such a material has been reported based on model calculations[H. Ishizuka and Y. Motome, Phys. Rev. Lett. 109, 237207 (2012)], it remains unclear what material system might realize such an exotic state. Using first-principles calculations, we show that the experimentally accessible Mn intercalated epitaxial gr…
Collagen micro fibrils bio mimetically intercalate graphitic structures in aqueous media to form graphene nano platelets collagen complex (G Cl). Synthesized G Cl based stable, aqueous bio nanocolloids exhibit anomalously augmented charge transportation capabilities over simple collagen or graphene based colloids. The concentration tunable electrical transport properties of synthesized aqueous G Cl bio nanocolloids has been experimentally observed, theoretically analyzed and mathematically modeled. A comprehensive approach to mathematically predict the electrical transport properties of simple…
In this paper, we study the morphologic interaction between graphene and Si nanowires on a SiO2 substrate, using molecular mechanics simulations. Two cases are considered: 1) a graphene nanoribbon intercalated by a single Si nanowire on a SiO2 substrate and 2) a blanket graphene flake intercalated by an array of Si nanowires evenly patterned in parallel on a SiO2 substrate. Various graphene morphologies emerge from the simulation results of these two cases, which are shown to depend on both geometric parameters (e.g., graphene nanoribbon width, nanowire diameter, and nanowire spacing) and mate…
We present an orbital-resolved density functional theory study on the electronic properties of hydrogen and lithium intercalated graphene grown on the Si face of SiC. Starting from the $(6\sqrt3\times6\sqrt3)R30^{\circ}$ surface reconstruction of the graphene/SiC heterosystem, we find that both H and Li can restore the ideal structural characteristics of the two nonequivalent junction parts (i.e. graphene and the SiC substrate) when inserted at the interface. However, the chemical/electrostatic interactions remain different for the two cases. Hence, H-intercalated epitaxial graphene is subject…
It is highly desirable to integrate graphene into existing semiconductor technology, where the combined system is thermodynamically stable yet maintain a Dirac cone at the Fermi level. Firstprinciples calculations reveal that a certain transition metal (TM) intercalated graphene/SiC(0001), such as the strongly-bound graphene/intercalated-Mn/SiC, could be such a system. Different from free-standing graphene, the hybridization between graphene and Mn/SiC leads to the formation of a dispersive Dirac cone of primarily TM d characters. The corresponding Dirac spectrum is still isotropic, and the tr…
The field of plasmonics seeks to find materials with an intensive plasmon (large plasmon pole weight) with low Landau, phonon and other losses (small decay width). In this paper we propose a new class of materials that show exceptionally good plasmonic properties. These materials consist of van der Waals stacked 'plasmon active' layers (atomically thin metallic layers) and 'supporting' layers (atomically thin wide band gap insulating layers). One such material that can be experimentally realized - lithium intercalated hexagonal boron-nitride is studied in detail. We show that its 2D plasmon in…
We use density functional theory to determine the equilibrium shape of graphene flakes, through the calculation of the edge orientation dependence of the edge energy and edge stress of graphene nanoribbons. The edge energy is a nearly linear function of edge orientation angle; increasing from the armchair orientation to the zigzag orientation. Reconstruction of the zigzag edge lowers its energy to less than that of the armchair edge. The edge stress for all edge orientations is compressive, however, reconstruction of the zigzag edge reduces this edge stress to near zero. Hydrogen adsorption is…
Magnetic domain structure and spin-dependent reflectivity measurements on cobalt thin films intercalated at the graphene / Ir(111) interface are investigated using spin-polarised low-energy electron microscopy. We find that graphene-covered cobalt films have surprising magnetic properties. Vectorial imaging of magnetic domains reveals an unusually gradual thickness-dependent spin reorientation transition, in which magnetisation rotates from out-of-the-film plane to the in-plane direction by less than 10$^\circ$ per cobalt monolayer. During this transition, cobalt films have a meandering spin t…
We show the successful intercalation of large area (1 cm$^2$) epitaxial few-layer graphene grown on 4H-SiC with FeCl$_3$. Upon intercalation the resistivity of this system drops from an average value of $\approx 200 \ Ω/sq$ to $\approx 16 \ Ω/sq$ at room temperature. The magneto-conductance shows a weak localization feature with a temperature dependence typical of graphene Dirac fermions demonstrating the decoupling into parallel hole gases of each carbon layer composing the FeCl$_3$ intercalated structure. The phase coherence length ($\approx 1.2 μ$m at 280 mK) decreases rapidly only for temp…
Electron transport in a graphene quantum well can be analogous to photon transmission in an optical fiber. In this work, we present a detailed theoretical analysis to study the transport characteristics of graphene waveguides under the influence of different edge orientations. Non-equilibrium Green's function approach in combination with tight-binding Hamiltonian has been utilized to investigate the conductance properties of straight armchair and zigzag oriented graphene waveguides. Conductance plateaus at integer steps of $4e^2/h$ have been observed in both orientations while the zigzag orien…
On the basis of the Kubo formula we evaluated the optical conductivity of a graphene sheet. The full behavior of frequency as well as temperature dependence of the optical conductivity is presented. We show that the anisotropy of conductivity can be significantly enhanced at high frequencies. The photon absorption depends on the field polarization direction. At the frequency comparable to the maximum separation of upper and lower bands the photon-induced conduction of electrons is strongly suppressed if the polarization of field is along the zigzag direction. The corresponding optical conducti…
Organic charge-transfer complexes (CTCs) formed by strong electron acceptor and strong electron donor molecules are known to exhibit exotic effects such as superconductivity and charge density waves. We present a low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) study of a two-dimensional (2D) monolayer CTC of tetrathiafulvalene (TTF) and fluorinated tetracyanoquinodimethane (F4TCNQ), self-assembled on the surface of oxygen-intercalated epitaxial graphene on Ir(111) (G/O/Ir(111)). We confirm the formation of the charge-transfer complex by dI/dV spectroscopy and direct…
Two-dimensional confinement of lattices produces a variety of order and disorder phenomena. When the confining walls have atomic granularity, unique structural phases are expected, of relevance in nanotribology, porous materials or intercalation compounds where \textit{e.g.} electronic states can emerge accordingly. The interlayer's own order is frustrated by the competing interactions exerted by the two confining surfaces. We revisit the concept of orientational ordering, introduced by Novaco and McTague to describe the twist of incommensurate monolayers on crystalline surfaces. We predict a …
We present a comprehensive study of graphene grown by chemical vapor deposition on copper single crystals with exposed (100), (110) and (111) faces. Direct examination of the as-grown graphene by Raman spectroscopy using a range of visible excitation energies and microRaman mapping shows distinct strain and doping levels for individual Cu surfaces. Comparison of results from Raman mapping with X-ray diffraction techniques and Atomic Force Microscopy shows it is neither the crystal quality nor the surface topography responsible for the specific strain and doping values, but it is the Cu lattice…
Zhang et al. reported in [Phys. Rev. B 77, 241402(R) (2008)] a theoretical study of the optical spectra of monolayer graphene employing the Kubo formula within a tight-binding model. Their calculations predicted that at high frequencies the optical conductivity of graphene becomes strongly anisotropic. In particular, at frequencies comparable to the energy separation of the upper and lower bands at the $Γ$-point, the optical conductivity is strongly suppressed if the field polarization is along the zigzag direction while it is significantly high for the armchair one. We find that, unfortunatel…
We propose spin valves where a 2D non-magnetic conductor is intercalated between two ferromagnetic insulating layers. In this setup, the relative orientation of the magnetizations of the insulating layers can have a strong impact on the in-plane conductivity of the 2D conductor. We first show this for a graphene bilayer, described with a tight-binding model, placed between two ferromagnetic insulators. In the anti-parallel configuration, a band gap opens at the Dirac point, whereas in the parallel configuration, the graphene bilayer remains conducting. We then compute the electronic structure …
The introduction of 'twist' or relative rotation between two atomically thin van der Waals (vdW) membranes gives rise to periodic Moire potential, leading to a substantial altercation of the band structure of the planar assembly. While most of the recent experiments primarily focus on the electronic-band hybridization by probing in-plane transport properties, here we report out-of-plane thermoelectric measurements across the van der Waals gap in twisted bilayer graphene (tBLG), which exhibits an interplay of twist-dependent inter-layer electronic and phononic hybridization. We show that at a l…
We report observation of graphene plasmon interference fringes across a wide spectral range using a scattering scanning near-field optical microscope (s-SNOM) that employs a widely tunable bank of quantum cascade lasers. We use plasmon interference to measure the dispersion curve of graphene plasmons over more than an order of magnitude of plasmon wavelength, from $λ_{sp}$ ~140 to ~1700 nm, and extract the electron Fermi energy of 298$\pm$4 meV for hydrogen-intercalated single layer epitaxial graphene on SiC. Furthermore, we demonstrate the appearance of wavelength tuneable graphene plasmon re…
