Results for "A. K. Geim"

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The rise of grapheneFeb 26 2007Graphene is a rapidly rising star on the horizon of materials science and condensed matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality and, despite its short history, has already revealed ... More
Electron scattering on microscopic corrugations in grapheneJun 17 2007Sep 11 2007We discuss various scattering mechanisms for Dirac fermions in single-layer graphene. It is shown that scattering on a short-range potential (due to, for example, neutral impurities) is mostly irrelevant for electronic quality of graphene, which is likely ... More
Chiral tunneling and the Klein paradox in grapheneApr 12 2006Aug 14 2006The so-called Klein paradox - unimpeded penetration of relativistic particles through high and wide potential barriers - is one of the most exotic and counterintuitive consequences of quantum electrodynamics (QED). The phenomenon is discussed in many ... More
Energy gaps, topological insulator state and zero-field quantum Hall effect in graphene by strain engineeringSep 09 2009Among many remarkable qualities of graphene, its electronic properties attract particular interest due to a massless chiral character of charge carriers, which leads to such unusual phenomena as metallic conductivity in the limit of no carriers and the ... More
Scattering of electrons by clusters of charged impurities in grapheneJan 10 2009May 25 2009It is shown that clustering of charged impurities on graphene can suppress their contribution to the resistivity by a large factor of about the number of impurities per cluster, while leaving the density dependence unchanged. If the cluster size is large ... More
Fine Structure in Magnetization of Individual Fluxoid StatesJan 11 2000Each time a vortex enters or exits a small superconductor, a different fluxoid state develops. We have observed splitting and sharp kinks on magnetization curves of such individual states. The features are the manifestation of first and second order transitions, ... More
The optical conductivity of graphene in the visible region of the spectrumMar 12 2008Aug 27 2008We compute the optical conductivity of graphene beyond the usual Dirac cone approximation, giving results that are valid in the visible region of the conductivity spectrum. The effect of next nearest neighbor hoping is also discussed. Using the full expression ... More
Giant Spin-Hall Effect induced by Zeeman Interaction in GrapheneMar 24 2011We propose a new approach to generate and detect spin currents in graphene, based on a large spin-Hall response arising near the neutrality point in the presence of external magnetic field. Spin currents result from the imbalance of the Hall resistivity ... More
The electronic properties of grapheneSep 07 2007Feb 29 2008This article reviews the basic theoretical aspects of graphene, a one atom thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic ... More
Cyclotron Resonance study of the electron and hole velocity in graphene monolayersApr 03 2007Jul 11 2007We report studies of cyclotron resonance in monolayer graphene. Cyclotron resonance is detected using the photoconductive response of the sample for several different Landau level occupancies. The experiments measure an electron velocity at the K- (Dirac) ... More
Room-temperature electric field effect and carrier-type inversion in graphene filmsOct 25 2004The ability to control electronic properties of a material by externally applied voltage is at the heart of modern electronics. In many cases, it is the so-called electric field effect that allows one to vary the carrier concentration in a semiconductor ... More
Raman Fingerprint of Charged Impurities in GrapheneSep 17 2007We report strong variations in the Raman spectra for different single-layer graphene samples obtained by micromechanical cleavage, which reveals the presence of excess charges, even in the absence of intentional doping. Doping concentrations up to ~10^13 ... More
Unimpeded permeation of water through helium-leak-tight graphene-based membranesDec 15 2011Permeation through nanometer pores is important in the design of materials for filtration and separation techniques and because of unusual fundamental behavior arising at the molecular scale. We found that submicron-thick membranes made from graphene ... More
Magnetization of mesoscopic superconducting discsJul 02 1997Oct 07 1997Solutions of Ginzburg-Landau eqns. coupled with three dimensional Maxwell eqns. reveal intriguing magnetic response of small superconducting particles, qualitatively different from the two dimensional approximation but in agreement with recent experiments. ... More
Generic Miniband Structure of Graphene on a Hexagonal SubstrateNov 20 2012May 02 2013Using a general symmetry-based approach, we provide a classification of generic miniband structures for electrons in graphene placed on substrates with the hexagonal Bravais symmetry. In particular, we identify conditions at which the first moir\'e miniband ... More
Graphene Spin Valve DevicesApr 24 2007Graphene - a single atomic layer of graphite - is a recently-found two-dimensional form of carbon, which exhibits high crystal quality and ballistic electron transport at room temperature. Soft magnetic NiFe electrodes have been used to inject polarized ... More
Stacking boundaries and transport in bilayer grapheneNov 18 2013Mar 13 2014Pristine bilayer graphene behaves in some instances as an insulator with a transport gap of a few meV. This behaviour has been interpreted as the result of an intrinsic electronic instability induced by many-body correlations. Intriguingly, however, some ... More
Generating quantizing pseudomagnetic fields by bending graphene ribbonsOct 30 2009We analyze the mechanical deformations that are required to create uniform pseudomagnetic fields in graphene. It is shown that, if a ribbon is bent in-plane into a circular arc, this can lead to fields exceeding 10T, which is sufficient for the observation ... More
Two Dimensional Atomic CrystalsMar 21 2005We report free-standing atomic crystals that are strictly 2D and can be viewed as individual atomic planes pulled out of bulk crystals or as unrolled single-wall nanotubes. By using micromechanical cleavage, we have prepared and studied a variety of 2D ... More
Subatomic movements of a domain wall in the Peierls potentialDec 24 2003Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice ... More
Scalable and efficient separation of hydrogen isotopes using graphene-based electrochemical pumpingFeb 24 2017May 17 2017Thousands of tons of isotopic mixtures are processed annually for heavy-water production and tritium decontamination. The existing technologies remain extremely energy intensive and require large capital investments. New approaches are needed to reduce ... More
Indirect excitons in van der Waals heterostructures at room temperatureSep 20 2017Indirect excitons (IXs) in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by a high binding energy making them stable at room temperature and giving the opportunity for exploring fundamental phenomena in excitonic ... More
Resonant scattering by realistic impurities in grapheneMar 02 2010Jul 29 2010We develop a first-principles theory of resonant impurities in graphene and show that a broad range of typical realistic impurities leads to the characteristic sublinear dependence of the conductivity on the carrier concentration. By means of density ... More
Graphene bubbles on a substrate : Universal shape and van der Waals pressureApr 01 2016Trapped substances between a 2D crystal, such as graphene, and an atomically flat substrate, for example, hexagonal boron nitride, give rise to the formation of bubbles. We show that the size, shape and internal pressure inside these bubbles are determined ... More
Revealing common artifacts due to ferromagnetic inclusions in highly-oriented pyrolytic graphiteJan 30 2012We report on an extensive investigation to figure out the origin of room-temperature ferromagnetism that is commonly observed by SQUID magnetometry in highly-oriented pyrolytic graphite (HOPG). Electron backscattering and X-ray microanalysis revealed ... More
A graphene-based electrochemical switchDec 12 2007Conventional field effect transistor operation in graphene is limited by its zero gap and minimum quantum conductivity. In this work, we report on controlled electrochemical modification of graphene such that its conductance changes by more than six orders ... More
Magnetophonon resistance oscillations in graphene and carrier screening of the longitudinal acoustic modesMay 09 2019Recently observed magnetophonon resonances in the magnetoresistance of graphene are investigated using the Kubo formalism. This analysis provides a quantitative fit to the experimental data over a wide range of carrier densities. It demonstrates the predominance ... More
Magnetophonon spectroscopy of Dirac Fermion scattering by transverse and longitudinal acoustic phonons in grapheneMay 09 2019May 29 2019Recently observed magnetophonon resonances in the magnetoresistance of graphene are investigated using the Kubo formalism. This analysis provides a quantitative fit to the experimental data over a wide range of carrier densities. It demonstrates the predominance ... More
Reply to Comment by D. Spemann et al [EPL 98 (2012) 57006, arXiv:1204.2992]Jun 20 2012This article is a reply to the Comment by D. Spemann et al (arXiv:1204.2992) in response to our paper 'Revealing common artifacts due to ferromagnetic inclusions in highly oriented pyrolytic graphite' (EPL, 97 (2012) 47001).
Thermal conductivity of graphene in Corbino membrane geometryMar 18 2010Local laser excitation and temperature readout from the intensity ratio of Stokes to anti-Stokes Raman scattering signals are employed to study the thermal properties of a large graphene membrane. The concluded value of the heat conductivity coefficient ... More
Multiple flux jumps and irreversible behavior of thin Al superconducting ringsSep 11 2002An experimental and theoretical investigation was made of flux jumps and irreversible magnetization curves of mesoscopic Al superconducting rings. In the small magnetic field region the change of vorticity with magnetic field can be larger than unity. ... More
Non-volatile switching in graphene field effect devicesMay 27 2008The absence of a band gap in graphene restricts its straight forward application as a channel material in field effect transistors. In this letter, we report on a new approach to engineer a band gap in graphene field effect devices (FED) by controlled ... More
Commensurability Effects in Viscosity of Nanoconfined WaterJan 09 2016Mar 20 2016The rate of water flow through hydrophobic nanocapillaries is greatly enhanced as compared to that expected from macroscopic hydrodynamics. This phenomenon is usually described in terms of a relatively large slip length, which is in turn defined by such ... More
Impermeable Barrier Films and Protective Coatings Based on Reduced Graphene OxideMay 09 2014Barrier films preventing permeation of gases and moistures are important for many industries ranging from food to medical and from chemical to electronic. From this perspective, graphene has recently attracted particular interest because its defect free ... More
Infrared spectroscopy of electronic bands in bilayer grapheneOct 14 2008Nov 02 2008We present infrared spectra (0.1-1 eV) of electrostatically gated bilayer graphene as a function of doping and compare it with tight binding calculations. All major spectral features corresponding to the expected interband transitions are identified in ... More
Scaling of the quantum-Hall plateau-plateau transition in grapheneAug 04 2009The temperature dependence of the magneto-conductivity in graphene shows that the widths of the longitudinal conductivity peaks, for the N=1 Landau level of electrons and holes, display a power-law behavior following $\Delta \nu \propto T^{\kappa}$ with ... More
Two Dimensional Electron and Hole Gases at the Surface of GraphiteMay 12 2005We report high-quality two-dimensional (2D) electron and hole gases induced at the surface of graphite by the electric field effect. The 2D carriers reside within a few near-surface atomic layers and exhibit mobilities up to 15,000 and 60,000 cm2/Vs at ... More
Single Layer Behavior and Its Breakdown in Twisted Graphene LayersOct 19 2010We report high magnetic field scanning tunneling microscopy and Landau level spectroscopy of twisted graphene layers grown by chemical vapor deposition. For twist angles exceeding ~3 degrees the low energy carriers exhibit Landau level spectra characteristic ... More
Graphene bubbles with controllable curvatureAug 08 2011Aug 25 2011Raised above the substrate and elastically deformed areas of graphene in the form of bubbles are found on different substrates. They come in a variety of shapes, including those which allow strong modification of the electronic properties of graphene. ... More
On the roughness of single- and bi-layer graphene membranesMar 01 2007We present a detailed transmission electron microscopy and electron diffraction study of the thinnest possible membrane, a single layer of carbon atoms suspended in vacuum and attached only at its edges. Membranes consisting of two graphene layers are ... More
Lifting of the Landau level degeneracy in graphene devices in a tilted magnetic fieldNov 26 2015We report on transport and capacitance measurements of graphene devices in magnetic fields up to 30 T. In both techniques, we observe the full splitting of Landau levels and we employ tilted field experiments to address the origin of the observed broken ... More
The effect of electron dielectric response on the quantum capacitance of graphene in a strong magnetic fieldJul 08 2013The quantum capacitance of graphene can be negative when the graphene is placed in a strong magnetic field, which is a clear experimental signature of positional correlations between electrons. Here we show that the quantum capacitance of graphene is ... More
Graphene-hexagonal boron nitride resonant tunneling diodes as high-frequency oscillatorsJun 16 2015Mar 22 2016We assess the potential of two-terminal graphene-hBN-graphene resonant tunneling diodes as high-frequency oscillators, using self-consistent quantum transport and electrostatic simulations to determine the time-dependent response of the diodes in a resonant ... More
Giant Intrinsic Carrier Mobilities in Graphene and Its BilayerOct 28 2007Jan 07 2008We have studied temperature dependences of electron transport in graphene and its bilayer and found extremely low electron-phonon scattering rates that set the fundamental limit on possible charge carrier mobilities at room temperature. Our measurements ... More
Non-Quantized Penetration of Magnetic Field in the Vortex State of SuperconductorsSep 08 2000As first pointed out by Bardeen and Ginzburg in the early sixties, the amount of magnetic flux carried by vortices depends on their distance to the sample edge and can be smaller than one flux quantum, f0 = h/2e. In bulk superconductors, this reduction ... More
Chaotic Dirac billiard in graphene quantum dotsDec 30 2007We report on transport characteristics of quantum dot devices etched entirely in graphene. At large sizes, they behave as conventional single-electron transistors, exhibiting periodic Coulomb blockade peaks. For quantum dots smaller than 100 nm, the peaks ... More
Density of states and zero Landau level probed through capacitance of grapheneMay 26 2010We report capacitors in which a finite electronic compressibility of graphene dominates the electrostatics, resulting in pronounced changes in capacitance as a function of magnetic field and carrier concentration. The capacitance measurements have allowed ... More
Spectroscopic ellipsometry of graphene and an exciton-shifted van Hove peak in absorptionMar 12 2010Apr 06 2010We demonstrate that optical transparency of any two-dimensional system with a symmetric electronic spectrum is governed by the fine structure constant and suggest a simple formula that relates a quasi-particle spectrum to an optical absorption of such ... More
Strong suppression of weak (anti)localization in grapheneMar 30 2006Jun 29 2006Low-field magnetoresistance is ubiquitous in low-dimensional metallic systems with high resistivity and well understood as arising due to quantum interference on self-intersecting diffusive trajectories. We have found that in graphene this weak-localization ... More
Scaling approach to tight-binding transport in realistic graphene devices: the case of transverse magnetic focusingMay 23 2016Ultra-clean graphene sheets encapsulated between hexagonal boron nitride crystals host two-dimensional electron systems in which low-temperature transport is solely limited by the sample size. We revisit the theoretical problem of carrying out microscopic ... More
Detection of Individual Gas Molecules Absorbed on GrapheneOct 29 2006Aug 19 2007The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been ... More
The structure of suspended graphene sheetsJan 16 2007The recent discovery of graphene has sparked significant interest, which has so far been focused on the peculiar electronic structure of this material, in which charge carriers mimic massless relativistic particle. However, the structure of graphene - ... More
Circular dichroism of magneto-phonon resonance in doped grapheneJul 30 2012Nov 04 2012Polarization resolved, Raman scattering response due to E$_{2g}$ phonon in monolayer graphene has been investigated in magnetic fields up to 29 T. The hybridization of the E$_{2g}$ phonon with only the fundamental inter Landau level excitation (involving ... More
Dissipative Quantum Hall Effect in Graphene near the Dirac PointFeb 06 2007We report on the unusual nature of nu=0 state in the integer quantum Hall effect (QHE) in graphene and show that electron transport in this regime is dominated by counter-propagating edge states. Such states, intrinsic to massless Dirac quasiparticles, ... More
Control of excitons in multi-layer van der Waals heterostructuresOct 15 2015Dec 15 2015We report an experimental study of excitons in a double quantum well van der Waals heterostructure made of atomically thin layers of \Mo* and hexagonal boron nitride (hBN). The emission of neutral and charged excitons is controlled by gate voltage, temperature, ... More
Strong Plasmonic Enhancement of Photovoltage in GrapheneJul 21 2011Amongst the wide spectrum of potential applications of graphene, ranging from transistors and chemical-sensors to nanoelectromechanical devices and composites, the field of photonics and optoelectronics is believed to be one of the most promising. Indeed, ... More
Sub-bandgap voltage electroluminescence and magneto-oscillations in a WSe2 light-emitting van der Waals heterostructureFeb 27 2017We report on experimental investigations of an electrically driven WSe2 based light-emitting van der Waals heterostructure. We observe a threshold voltage for electroluminescence significantly lower than the corresponding single particle band gap of monolayer ... More
Limits on intrinsic magnetism in grapheneJul 02 2010Nov 23 2010We have studied magnetization of graphene nanocrystals obtained by sonic exfoliation of graphite. No ferromagnetism is detected at any temperature down to 2 K. Neither do we find strong paramagnetism expected due to the massive amount of edge defects. ... More
Electrochemically Top Gated Graphene: Monitoring Dopants by Raman ScatteringSep 08 2007We demonstrate electrochemical top gating of graphene by using a solid polymer electrolyte. This allows to reach much higher electron and hole doping than standard back gating. In-situ Raman measurements monitor the doping. The G peak stiffens and sharpens ... More
Direct Observation of Vortex Shells and Magic Numbers in Mesoscopic Superconducting DisksJun 24 2005We have visualised and studied vortex configurations in mesoscopic superconducting disks using the Bitter decoration technique. For a broad range of vorticities L the circular geometry is found to result in the formation of concentric shells of vortices. ... More
Subjecting a graphene monolayer to tension and compressionOct 04 2009The mechanical behaviour of graphene flakes under both tension and compression is examined using a cantilever-beam arrangement. Two different sets of samples were employed involving flakes just supported on a plastic bar but also embedded within the plastic ... More
Anomalously low dielectric constant of confined waterJun 12 2018The dielectric constant of interfacial water has been predicted to be smaller than that of bulk water (= 80) because the rotational freedom of water dipoles is expected to decrease near surfaces, yet experimental evidence is lacking. We report local capacitance ... More
Making Graphene LuminescentSep 20 2009We show that strong photoluminescence (PL) can be induced in single-layer graphene on using an oxygen plasma treatment. PL characteristics are spatially uniform across the flakes and connected to elastic scattering spectra distinctly different from those ... More
Micrometer-scale ballistic transport in encapsulated graphene at room temperatureMar 23 2011Jun 10 2011Devices made from graphene encapsulated in hexagonal boron-nitride exhibit pronounced negative bend resistance and an anomalous Hall effect, which are a direct consequence of room-temperature ballistic transport on a micrometer scale for a wide range ... More
Strong Coulomb drag and broken symmetry in double-layer grapheneJun 28 2012Spatially separated electron systems remain strongly coupled by electron-electron interactions even when they cannot exchange particles, provided that the layer separation d is comparable to a characteristic distance l between charge carriers within layers. ... More
Gap opening in the zeroth Landau level of grapheneApr 06 2009We have measured a strong increase of the low-temperature resistivity $\rho_{xx}$ and a zero-value plateau in the Hall conductivity $\sigma_{xy}$ at the charge neutrality point in graphene subjected to high magnetic fields up to 30 T. We explain our results ... More
Surface Enhanced Raman Spectroscopy of GrapheneMay 18 2010Surface enhanced Raman scattering (SERS) exploits surface plasmons induced by the incident field in metallic nanostructures to significantly increase the Raman intensity. Graphene provides the ideal prototype two dimensional (2d) test material to investigate ... More
Complete steric exclusion of ions and proton transport through confined monolayer waterNov 22 2018Dec 21 2018It has long been an aspirational goal to create artificial structures that allow fast permeation of water but reject even the smallest hydrated ions, replicating the feat achieved by nature in protein channels (e.g., aquaporins). Despite recent progress ... More
Influence of metal contacts and charge inhomogeneity on transport properties of graphene near the neutrality pointNov 10 2008Jun 20 2009There is an increasing amount of literature concerning electronic properties of graphene close to the neutrality point. Many experiments continue using the two-probe geometry or invasive contacts or do not control samples' macroscopic homogeneity. We ... More
Effect of high-k environment on charge carrier mobility in grapheneSep 06 2008May 08 2009It is widely assumed that the dominant source of scattering in graphene is charged impurities in a substrate. We have tested this conjecture by studying graphene placed on various substrates and in high-k media. Unexpectedly, we have found no significant ... More
Singular-phase nanooptics: towards label-free single molecule detectionApr 16 2014Non-trivial topology of phase is crucial for many important physics phenomena such as, for example, the Aharonov-Bohm effect 1 and the Berry phase 2. Light phase allows one to create "twisted" photons 3, 4 , vortex knots 5, dislocations 6 which has led ... More
Making graphene visibleMay 02 2007Sep 22 2007Microfabrication of graphene devices used in many experimental studies currently relies on the fact that graphene crystallites can be visualized using optical microscopy if prepared on top of silicon wafers with a certain thickness of silicon dioxide. ... More
Resonant tunnelling and negative differential conductance in graphene transistorsMar 27 2013May 01 2013The chemical stability of graphene and other free-standing two-dimensional crystals means that they can be stacked in different combinations to produce a new class of functional materials, designed for specific device applications. Here we report resonant ... More
Cross-sectional imaging of individual layers and buried interfaces of graphene-based heterostructures and superlatticesJun 28 2012Sep 04 2012By stacking various two-dimensional (2D) atomic crystals [1] on top of each other, it is possible to create multilayer heterostructures and devices with designed electronic properties [2-5]. However, various adsorbates become trapped between layers during ... More
Two-Dimensional Gas of Massless Dirac Fermions in GrapheneSep 13 2005Electronic properties of materials are commonly described by quasiparticles that behave as non-relativistic electrons with a finite mass and obey the Schroedinger equation. Here we report a condensed matter system where electron transport is essentially ... More
Ballistic molecular transport through two-dimensional channelsMay 15 2018Gas permeation through nanoscale pores is ubiquitous in nature and plays an important role in a plethora of technologies. Because the pore size is typically smaller than the mean free path of gas molecules, their flow is conventionally described by the ... More
From One Electron to One Hole: Quasiparticle Counting in Graphene Quantum Dots Determined by Electrochemical and Plasma EtchingJul 26 2010Graphene is considered to be a promising material for future electronics. The envisaged transistor applications often rely on precision cutting of graphene sheets with nanometer accuracy. In this letter we demonstrate graphene-based quantum dots created ... More
Electric Field Effect in Atomically Thin Carbon FilmsOct 21 2004We report a naturally-occurring two-dimensional material (graphene that can be viewed as a gigantic flat fullerene molecule, describe its electronic properties and demonstrate all-metallic field-effect transistor, which uniquely exhibits ballistic transport ... More
Accurate determination of electron-hole asymmetry and next-nearest neighbor hopping in grapheneSep 11 2013Sep 15 2013The next-nearest neighbor hopping term t' determines a magnitude and, hence, importance of several phenomena in graphene, which include self-doping due to broken bonds and the Klein tunneling that in the presence of t' is no longer perfect. Theoretical ... More
Graphene as a transparent conductive support for studying biological molecules by transmission electron microscopyOct 23 2010We demonstrate the application of graphene as a support for imaging individual biological molecules in transmission electron microscope (TEM). A simple procedure to produce free-standing graphene membranes has been designed. Such membranes are extremely ... More
The Raman Fingerprint of GrapheneJun 12 2006Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensionality. It can be stacked into 3d graphite, rolled into 1d nanotubes, or wrapped into 0d fullerenes. Its recent discovery in free state has finally provided ... More
Molecular Doping of GrapheneMar 15 2007Graphene, a one-atom thick zero gap semiconductor [1, 2], has been attracting an increasing interest due to its remarkable physical properties ranging from an electron spectrum resembling relativistic dynamics [3-12] to ballistic transport under ambient ... More
Gate tunable charged-phonon effect in bilayer grapheneJun 11 2009Sep 10 2009We observe a giant increase of the infrared intensity and a softening of the in-plane antisymmetric phonon mode Eu (~0.2 eV) in bilayer graphene as a function of the gate-induced doping. The phonon peak has a pronounced Fano-like asymmetry. We suggest ... More
Macroscopic graphene membranes and their extraordinary stiffnessMay 13 2008Jun 18 2008The properties of suspended graphene are currently attracting enormous interest, but the small size of available samples and the difficulties in making them severely restrict the number of experimental techniques that can be used to study the optical, ... More
Transport of hydrogen isotopes through interlayer spacing in van der Waals crystalsFeb 09 2018Atoms start behaving as waves rather than classical particles if confined in spaces commensurate with their de Broglie wavelength. At room temperature this length is only about one angstrom even for the lightest atom, hydrogen. This restricts quantum-confinement ... More
Quantum Hall activation gaps in bilayer grapheneSep 28 2010Oct 08 2010We have measured the quantum Hall activation gaps in bilayer graphene at filling factors $\nu=\pm4$ and $\nu=\pm8$ in high magnetic fields up to 30 T. We find that energy levels can be described by a 4-band relativistic hyperbolic dispersion. The Landau ... More
Magnetotransport in single layer graphene in a large parallel magnetic fieldFeb 04 2016Jul 18 2016Graphene on hexagonal boron-nitride (h-BN) is an atomically flat conducting system that is ideally suited for probing the effect of Zeeman splitting on electron transport. We demonstrate by magneto-transport measurements that a parallel magnetic field ... More
Limits on electron quality in suspended graphene due to flexural phononsAug 15 2010The temperature dependence of the mobility in suspended graphene samples is investigated. In clean samples, flexural phonons become the leading scattering mechanism at temperature $T \gtrsim 10\,\,$K, and the resistivity increases quadratically with $T$. ... More
Size effect in ion transport through angstrom-scale slitsSep 12 2017It has been an ultimate but seemingly distant goal of nanofluidics to controllably fabricate capillaries with dimensions approaching the size of small ions and water molecules. We report ion transport through ultimately narrow slits that are fabricated ... More
Quantum resistance metrology in grapheneOct 22 2008We have performed a metrological characterization of the quantum Hall resistance in a 1 $\mu$m wide graphene Hall-bar. The longitudinal resistivity in the center of the $\nu=\pm 2$ quantum Hall plateaus vanishes within the measurement noise of 20 m$\Omega$ ... More
Universal Dynamic Conductivity and Quantized Visible Opacity of Suspended GrapheneMar 26 2008We show that the optical transparency of suspended graphene is defined by the fine structure constant, alpha, the parameter that describes coupling between light and relativistic electrons and is traditionally associated with quantum electrodynamics rather ... More
Precise and ultrafast molecular sieving through graphene oxide membranesJan 14 2014There has been intense interest in filtration and separation properties of graphene-based materials that can have well-defined nanometer pores and exhibit low frictional water flow inside them. Here we investigate molecular permeation through graphene ... More
Sieving hydrogen isotopes through two dimensional crystalsNov 20 2015Jan 02 2016One-atom-thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. We show that monolayers of graphene and boron nitride can be used to separate hydrogen ion isotopes. Employing electrical measurements ... More
Failure of conductance quantization in two-dimensional topological insulators due to non-magnetic impuritiesJun 27 2018Jan 05 2019Despite topological protection and the absence of magnetic impurities, two-dimensional topological insulators display quantized conductance only in surprisingly short channels, which can be as short as 100 nm for atomically thin materials. We show that ... More
Room-Temperature Quantum Hall Effect in GrapheneFeb 17 2007The quantum Hall effect (QHE), one example of a quantum phenomenon that occur on a truly macroscopic scale, has been attracting intense interest since its discovery in 1980 and has helped elucidate many important aspects of quantum physics. It has also ... More
Localized bright luminescence of indirect excitons and trions in MoSe$_2$/WSe$_2$ van der Waals heterostructureJan 24 2019Indirect excitons (IX) in semiconductor heterostructures are bosons, which can cool below the temperature of quantum degeneracy and can be effectively controlled by voltage and light. IX quantum Bose gases and IX devices were explored in GaAs heterostructures ... More
Superconductivity in Ca-doped grapheneAug 27 2015Graphene, a zero-gap semimetal, can be transformed into a metallic, semiconducting or insulating state by either physical or chemical modification. Superconductivity is conspicuously missing among these states despite considerable experimental efforts ... More
Unconventional quantum Hall effect and Berry's phase of 2pi in bilayer grapheneFeb 23 2006There are known two distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems, and the other is its relativistic counterpart recently observed in graphene, where ... More
Dual origin of defect magnetism in graphene and its reversible switching by molecular dopingJan 31 2013May 10 2013A possibility to control magnetic properties by using electric fields is one of the most desirable characteristics for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is ... More
Unraveling the 3D atomic structure of a suspended graphene/hBN van der Waals heterostructureFeb 09 2017In this work we demonstrate that a free-standing van der Waals heterostructure, usually regarded as a flat object, can exhibit an intrinsic buckled atomic structure resulting from the interaction between two layers with a small lattice mismatch. We studied ... More