Recent experimental work on locally gated graphene layers resulting in p-n junctions have revealed quantum Hall effect in their transport behavior. We explain the observed conductance quantization which is fractional in the bipolar regime and integer in the unipolar regime in terms of quantum Hall edge modes propagating along and across the p-n interface. In the bipolar regime the electron and hole modes can mix at the p-n boundary, leading to current partition and quantized shot noise plateaus similar to those of conductance, while in the unipolar regime transport is noiseless. These quantum Hall phenomena reflect the massless Dirac character of charge carriers in graphene, with particle-hole interplay manifest in mode mixing and noise in the bipolar regime.
The linear conductance spectrum of a metallic graphene junction formed by interconnecting two gapless graphene nanoribbons is calculated. A strong conductance suppression appears in the vicinity of the Dirac point. We found that such a conductance suppression arises from the antiresonance effect associated with the edge state localized at the zigzag-edged shoulder of the junction. The conductance valley due to the antiresonance is rather robust in the presence of the impurity and vacancy scattering. And the center of the conductance valley can be readily tuned by an electric field exerted on t…
We developed a multi-level lithography process to fabricate graphene p-n-p junctions with the novel geometry of contactless, suspended top gates. This fabrication procedure minimizes damage or doping to the single atomic layer, which is only exposed to conventional resists and developers. The process does not require special equipment for depositing gate dielectrics or releasing sacrificial layers, and is compatible with annealing procedures that improve device mobility. Using this technique, we fabricate graphene devices with suspended local top gates, where the creation of high quality graph…
In this review we focus on the effect of the Dirac nature of graphene quasiparticles on two separate aspects. The first of these involves transport across superconducting graphene junctions with barriers of thickness $d_0$ and arbitrary gate voltages $V_0$ applied across the barrier region. The second aspect involves study of the presence of localized magnetic impurities in graphene and we show that Kondo effect in graphene is unconventional and can be tuned by gate voltage. We also discuss scanning tunneling conductance spectra phenomenon for both doped and undoped graphene. We show that the …
We have studied the interplay of an Anderson impurity in Landau quantized graphene, with special emphasis on the influence of the chemical potential. Within the slave-boson mean-field theory, we found reentrant Kondo behaviour by varying the chemical potential or gate voltage. Between Landau levels, the density of states is suppressed, and by changing the graphene's Fermi energy, we cross from metallic to semiconducting regions. Hence, the corresponding Kondo behaviour is also influenced. The f-level spectral function reveals both the presence of Landau levels in the conduction band and the Ko…
Using high quality graphene pnp junctions, we observe prominent conductance fluctuations on transitions between quantum Hall (QH) plateaus as the top gate voltage Vtg is varied. In the Vtg-B plane, the fluctuations form crisscrossing lines that are parallel to those of the adjacent plateaus, with different temperature dependences for the conductance peaks and valleys. These fluctuations arise from Coulomb-induced charging of electron- or hole-doped localized states when the device bulk is delocalized, underscoring the importance of electronic interactions in graphene in the QH regime.
We study the complete tunneling spectroscopy of a normal metal/$p$-wave superconductor junction ($N-pS$) and normal metal/heterostructure superconductor junction ($N-hS$) by Blonder-Tinkham-Klapwijk (BTK) method. We find that, for $p$-wave superconductor with non-trivial topology, there exists a quantized zero-bias conductance peak stably, for heterostructure superconductor with non-trivial topology, the emerging zero-bias conductance peak is non-quantized and usually has a considerable gap to the quantized value. Furthermore, it is sensitive to parameters, especially to spin-orbit coupling an…
We observe a dc electric current in response to terahertz radiation in lateral inter-digitated double-comb graphene p-n junctions. The junctions were fabricated by selective ultraviolet irradiation inducing p-type doping in intrinsic n-type epitaxial monolayer graphene. The photocurrent exhibits a strong polarization dependence and is explained by electric rectification in p-n junctions.
We study spin transport in normal/ferromagnetic/normal graphene junctions where a gate electrode is attached to the ferromagnetic graphene. We find that due to the exchange field of the ferromagnetic graphene, spin current through the junctions has an oscillatory behavior with respect to the chemical potential in the ferromagnetic graphene, which can be tuned by the gate voltage. Especially, we obtain a controllable spin current reversal by the gate voltage. Our prediction of high controllability of spin transport in ferromagnetic graphene junction may contribute to the development of the spin…
Using ab-initio methods we investigate the possibility of three-terminal graphene "T-junction" devices and show that these all-graphene edge contacts are energetically feasible when the 1D interface itself is free from foreign atoms. We examine the energetics of various junction structures as a function of the atomic scale geometry. Three-terminal equilibrium Green's functions are used to determine the transmission spectrum and contact resistance of the system. We find that the most symmetric structures have a significant binding energy, and we determine the contact resistances in the junction…
Thermopower of graphene-superconductor (GS) junction is analyzed within the extended Blonder- Tinkham-Klapwijk formalism. Within this approach we have also calculated the temperature de- pendence of the zero-bias conductance for GS junction. Both quantities reflect quasi-relativistic nature of massless Dirac fermions in graphene. Both, the linear and the non-linear regimes are considered.
We show that the wavefunctions form caustics in circular graphene p-n junctions which in the framework of geometrical optics can be interpreted with negative refractive index.
In this work, we investigate thermoelectric properties of junctions consisting of two partially overlapped graphene sheets coupled to each other in the cross-plane direction. It is shown that because of the weak van-der Waals interactions between graphene layers, the phonon conductance in these junctions is strongly reduced, compared to that of single graphene layer structures, while their electrical performance is weakly affected. By exploiting this effect, we demonstrate that the thermoelectric figure of merit can reach values higher than 1 at room temperature in junctions made of gapped gra…
Imperfections change essentially the electronic transport properties of graphene. Motivated by a recent experiment reporting on the possible application of graphene as junctions, we study transport properties in graphene-based junctions with single localized defect. We solve the Dirac-Bogoliubov-de-Gennes equation with a single localized defect superconductor-normal(graphene)-superconductor (SNS) junction. We consider the properties of tunneling conductance and Josephson current through an undoped strip of graphene with heavily doped s-wave superconducting electrodes in the dirty limit. We fin…
We show that an electrostatically created n-p junction separating the electron and hole gas regions in a graphene monolayer transmits only those quasiparticles that approach it almost perpendicularly to the n-p interface. Such a selective transmission of carriers by a single n-p junction would manifest itself in non-local magnetoresistance effect in arrays of such junctions and determines the unusual Fano factor in the current noise universal for the n-p junctions in graphene.
The proper understanding of semiconductor devices begins at the metal-semiconductor interface. The metal/semiconductor interface itself can also be an important device, as Schottky junctions often forms when the doping in the semiconductors is low. Here, we extend the analysis of metal-silicon Schottky junctions by using graphene, an atomically thin semimetal. We show that a fundamentally new transport model is needed to describe the graphene-silicon Schottky junction. While the current-voltage behavior follows the celebrated ideal diode behavior, the details of the diode characteristics is be…
We use the non-equilibrium Green function (NEGF) method in the ballistic limit to provide a quantitative description of the conductance of graphene pn junctions - an important building block for graphene electronics devices. In this paper, recent experiments on graphene junctions are explained by a ballistic transport model, but only if the finite junction transition width, Dw, is accounted for. In particular, the experimentally observed anamolous increase in the resistance asymmetry between nn and np junctions under low source/drain charge density conditions is also quantitatively captured by…
The focusing of electric current by a single \textit{p-n} junction in graphene is predicted. We show that precise focusing can be achieved by fine-tuning the densities of carriers on the n- and p-sides of the junction to equal values, whereas the current distribution in junctions with different densities resembles caustics in optics. This finding can be utilized in the engineering of electronic lenses and focused beam-splitters using gate-controlled \textit{n-p-n} junctions in graphene-based transistors.
We study by first-principles calculations a densely packed island of organic molecules (F4TCNQ) adsorbed on graphene. We find that with electron doping the island naturally forms a p-n junction in the graphene sheet. For example, a doping level of ~ 3 * 10^{13} electrons per cm^2 results in a p-n junction with 800 meV electrostatic potential barrier. Unlike in a conventional p-n junction in graphene, in the case of the junction formed by an adsorbed organic molecular island we expect that the Klein tunneling is inhibited, even without an applied external magnetic field. Here Klein tunneling is…
Focusing of electron waves in graphene p-n junctions is a striking manifestation of fermionic negative refraction. We analyze lensing in smooth p-n junctions and find that it differs in several interesting ways from that in the previously studied sharp p-n junctions. Most importantly, while the overall negative-refraction behavior remains unchanged, the image at the focal point undergoes additional broadening due to Klein tunneling in the junction. We develop a theory of image broadening and estimate the effect for practically interesting system parameter values.
The characteristics of tunnel junctions formed between n- and p-doped graphene are investigated theoretically. The single-particle tunnel current that flows between the two-dimensional electronic states of the graphene (2D-2D tunneling) is evaluated. At a voltage bias such that the Dirac points of the two electrodes are aligned, a large resonant current peak is produced. The magnitude and width of this peak is computed, and its use for devices is discussed. The influence of both rotational alignment of the graphene electrodes and structural perfection of the graphene is discussed.
Accessing intrinsic properties of a graphene device can be hindered by the influence of contact electrodes. Here, we capacitively couple graphene devices to superconducting resonant circuits and observe clear changes in the resonance- frequency and -widths originating from the internal charge dynamics of graphene. This allows us to extract the density of states and charge relaxation resistance in graphene p-n junctions without the need of electrical contacts. The presented characterizations pave a fast, sensitive and non-invasive measurement of graphene nanocircuits.
Transparent contact interfaces in superconductor-graphene hybrid systems are critical for realizing superconducting quantum applications. Here, we examine the effect of the edge-contact fabrication process on the transparency of the superconducting aluminum-graphene junction. We show significant improvement in the transparency of our superconductor-graphene junctions by promoting the chemical component of the edge contact etch process. Our results compare favorably with state-of-the-art graphene Josephson junctions. The findings of our study contribute to advancing the fabrication knowledge of…
We present direct measurements of the current-phase relation for lateral Josephson junctions with a graphene barrier, obtained by a phase-sensitive SQUID interferometry technique. We find that the current-phase relation is forward skewed with respect to the commonly observed sinusoidal behavior for short junctions in the quasi-ballistic transport regime, consistent with predictions for the behavior of Dirac fermions in a Josephson junction. The skewness increases with critical current and decreases sharply with increasing temperature.
We investigate critical current noise in short ballistic graphene Josephson junctions in the open-circuit gate-voltage limit within the McWorther model. We find flicker noise in a wide frequency range and discuss the temperature dependence of the noise amplitude as a function of the doping level. At the charge neutrality point we find a singular temperature dependence $T^{-3}$, strikingly different from the linear dependence expected for short ballistic graphene Josephson junctions under fixed gate voltage.
The stationary Josephson current in a ballistic graphene system is theoretically studied with focus on a planar junction consisting of a monolayer graphene sheet on top of which a pair of superconducting electrodes is deposited. To characterize such a planar junction, we employ two parameters: the coupling strength between the graphene sheet and the superconducting electrodes, and a potential drop induced in the graphene sheet by direct contact with the electrodes. We derive a general formula for the Josephson current by taking these parameters into account in addition to other basic parameter…
We have developed a process to fabricate suspended graphene devices with local bottom gates, and tested it by realizing electrostatically controlled pn junctions on a suspended graphene mono-layer nearly 2 micrometers long. Measurements as a function of gate voltage, magnetic field, bias, and temperature exhibit characteristic Fabry-Perot oscillations in the cavities formed by the pn junction and each of the contacts, with transport occurring in the ballistic regime. Our results demonstrate the possibility to achieve a high degree of control on the local electronic properties of ultra-clean su…
We demonstrate that the phenomenon of current confinement along graphene n-p junctions at high magnetic fields can be used to form an Aharonov-Bohm interferometer. The interference system exploits a closed n-p junction that can be induced by a floating gate within the sample, and coupling of the junction currents with the edge currents in the quantum Hall regime. Operation of the device requires current splitting at the edge and the n-p junction contacts which is found for armchair ribbons at low Fermi energy.
Usually, graphene is used in its horizontal directions to design novel concept devices. Here, we report a single electron tunneling diode based on quantum tunneling through a vertical graphene two-barrier junction. The junction is formed by positioning a scanning tunnelling microscopy (STM) tip above a graphene nanoribbon that was deposited on a graphite surface. Because of the asymmetry of the two-barrier junction, the electrons can unidirectional transfer from the tip to the graphene nanoribbon but not from the graphene to the tip. This result opens intriguing opportunities for designing new…
Combining experiment and theory, we investigate how the naturally created heterojunction at a graphene and metallic contact is modulated via interaction with molecular hydrogen (H2). Due to electrostatic interaction, a Cr/Au electrode induces a pn junction in graphene, leading to an asymmetrical resistance between the charge carriers (electron and hole). This asymmetry is well modeled by considering the preferential charge scattering at the pn junction, and we show that it can be modulated in a reversible, selective and asymmetrical manner by exposing H2 to the metal-graphene interface. Our re…
Graphene is believed to be an excellent candidate material for next-generation electronic devices. However, one needs to take into account the nontrivial effect of metal contacts in order to precisely control the charge injection and extraction processes. We have performed transport calculations for graphene junctions with wetting metal leads (metal leads that bind covalently to graphene) using nonequilibrium Green's functions and density functional theory. Quantitative information is provided on the increased resistance with respect to ideal contacts and on the statistics of current fluctuati…
We report on short ballistic (SB) Josephson coupling in junctions embedded in a planar heterostructure of graphene. Ballistic Josephson coupling is confirmed by the Fabry-Perot-type interference of the junction critical current $I_c$. An exceptionally large $I_cR_N$ product close to $2Δ_0/e$ ($R_N$; normal-state junction resistance, $Δ_0$ ; zero-temperature superconducting energy gap) is an indication of SB strong Josephson coupling. $I_c$ shows a temperature dependence inconsistent with the conventional short-junction-like behavior; $I_c(T)$ curves deviate systematically from the standard Kul…
Graphene nano-ribbons junctions based electronic devices are proposed in this Letter. Non-equilibrium Green function calculations show that nano-ribbon junctions tailored from single layer graphene with different edge shape and width can act as metal-semiconductor junctions and quantum dots can be implemented. In virtue of the possibilities of patterning monolayer graphene down to atomic precision, these structures, quite different from the previously reported two-dimensional bulk graphene or carbon nanotube devices, are expected to be used as the building blocks of the future nano-electronics…
We demonstrate ultra-sharp (${\lesssim}\,10\text{ nm}$) lateral $p\text{-}n$ junctions in graphene using electronic transport, scanning tunneling microscopy, and first principles calculations. The $p\text{-}n$ junction lies at the boundary between differentially-doped regions of a graphene sheet, where one side is intrinsic and the other is charge-doped by proximity to a flake of $α$-RuCl$_3$ across a thin insulating barrier. We extract the $p\text{-}n$ junction contribution to the device resistance to place bounds on the junction width. We achieve an ultra-sharp junction when the boundary bet…
We perform extensive analysis of graphene Josephson junctions embedded in microwave circuits. By comparing a diffusive junction at 15 mK with a ballistic one at 15 mK and 1 K, we are able to reconstruct the current-phase relation.
The stationary Josephson effect in a system of ballistic graphene is studied in the framework of quasiclassical Green's function theory. Reflecting the ultimate two-dimensionality of graphene, a Josephson junction involving a graphene sheet embodies what we call a planar Josephson junction, in which superconducting electrodes partially cover the two-dimensional graphene layer, achieving a planar contact with it. For capturing this feature we employ a model of tunneling Hamiltonian that also takes account of the effects of inhomogeneous carrier density. Within the effective mass approximation w…
We demonstrate the use of a quantum transport model to study heavily graded graphene p-n junctions in the quantum Hall regime. A combination of p-n interface roughness and delta function disorder potential allows us to compare experimental results on different devices from the literature. We find that wide p-n junctions suppress mixing of $n \neq 0$ Landau levels. Our simulations spatially resolve carrier transport in the device, for the first time, revealing separation of higher order Landau levels in strongly graded junctions, which suppresses mixing.
In this work we describe a proposal for a graphene-based nanostructure that modulates electric current even in the absence of a gap in the band structure. The device consists of a graphene p-n junction that acts as a Veselago lens that focuses ballistic electrons on the output lead. Applying external (electric and magnetic) fields changes the position of the output focus, reducing the transmission. Such device can be applied to low power field effect transistors, which can benefit from graphene's high electronic mobility.
We study the electronic transport in a graphene-based superconductor-normal(graphene)-superconductor (SNS) junction by use of the Dirac-Bogoliubov-de Gennes equation. We consider the properties of tunneling conductance through an undoped strip of graphene with heavily doped superconducting electrodes in the dirty limit. We find that spectrum of Andreev bound states are modified in the presence of single localized defect in the bulk. The minimum tunneling conductance remains the same and this result doesn't depend on the actual location of the imperfection.
Creation of sharp lateral p-n junctions in graphene devices, with transition widths well below the Fermi wavelength of graphene charge carriers, is vital to study and exploit these electronic systems for electron-optical applications. The achievement of such junctions is, however, not trivial due to the presence of a considerable out-of-plane electric field in lateral p-n junctions, resulting in large widths. Metal-graphene interfaces represent a novel, promising and easy to implement technique to engineer such sharp lateral p-n junctions in graphene field-effect devices, in clear contrast to …
We investigate adiabatic quantum pumping through a normal metal-insulator-superconductor (NIS) junction in a monolayer of graphene. The pumped current is generated by periodic modulation of two gate voltages, applied to the insulating and superconducting regions respectively. In the bilinear response regime and in the limit of a thin high insulating barrier, we find that the presence of the superconductor enhances the pumped current per mode by a factor of 4 at resonance. Compared to the pumped current in an analogous semiconductor NIS junction, the resonances have a $π/2$ phase difference. We…
We investigate the electronic properties of ballistic planar Josephson junctions with multiple superconducting terminals. Our devices consist of monolayer graphene encapsulated in boron nitride with molybdenum-rhenium contacts. Resistance measurements yield multiple resonant features, which are attributed to supercurrent flow among adjacent and non-adjacent Josephson junctions. In particular, we find that superconducting and dissipative currents coexist within the same region of graphene. We show that the presence of dissipative currents primarily results in electron heating and estimate the a…
We present a theoretical study of electron wave functions in ballistic circular n-p junctions of bilayer graphene. Similarly to the case of a circular n-p junction of monolayer graphene, we find that (i) the wave functions form caustics inside the circular region, and (ii) the shape of these caustics are well described by a geometrical optics model using the concept of a negative refractive index. In contrast to the monolayer case, we show that the strong focusing effect is absent in the bilayer. We explain these findings in terms of the angular dependence of Klein tunneling at a planar n-p ju…
We investigate the conductance of normal-conductor/graphene/normal-conductor (NGN) junctions for arbitrary on-site potentials in the normal and graphitic parts of the system. We find that a ballistic NGN junction can display insulating behavior even when the charge-carrier density in the graphene part is finite. This effect originates in the different k intervals supporting propagating modes in graphene and a normal conductor, and persists for moderate levels of bulk, edge, or interface disorder. The ensuing conductance thresholds could be used as an electronic tool to map out details of the g…
We study quasi-particle transmission through an $n $-$p$ junction in a graphene irradiated by an electromagnetic field (EF). In the absence of EF the electronic spectrum of undoped graphene is gapless, and one may expect the perfect transmission of quasi-particles flowing perpendicular to the junction. We demonstrate that the resonant interaction of propagating quasi-particles with the component of EF parallel to the junction induces a \textit{non-equilibrium dynamic gap} $(2Δ_R)$ between electron and hole bands in the quasi-particle spectrum of graphene. In this case the strongly suppressed q…
Metal-graphene-metal photodetectors utilize photocurrent generated near the graphene/metal junctions and have many advantages including high speed and broad-band operation. Here, we report on photocurrent generation at ABA/ABC stacking domain junctions in tri-layer graphene with a responsivity of 0.18 A/W. Unlike usual metal-graphene-metal devices, the photocurrent is generated in the middle of the graphene channel, not confined to the vicinity of the metal electrodes. The magnitude and the direction of the photocurrent depend on the back-gate bias. Theoretical calculations show that there is …
An algorithm is introduced for predicting quantized resistances in graphene p-n junction devices that utilize more than a single entry and exit point for electron flow. Depending on the configuration of an arbitrary number of terminals, electrical measurements yield fractional multiples of the typical quantized Hall resistance at the $ν=2$ plateau $R_H \approx 12906 Ω$ and take the form: $\frac{a}{b}R_H$. This theoretical formulation is independent of material, and applications to other material systems that exhibit quantum Hall behaviors are to be expected. Furthermore, this formulation is su…
In this paper we carry out a theoretical and experimental study of the nature of graphene/semiconductor Schottky contact. We present a simple and parameter-free carrier transport model of graphene/semiconductor Schottky contact derived from quantum statistical theory, which is validated by the quantum Landauer theory and first-principle calculations. The proposed model can well explain experimental results for samples of different types of graphene/semiconductor Schottky contact.
It has been shown in a recent study [Nguyen et al., Nanotechnol. \textbf{25}, 165201 (2014)] that unstrained/strained graphene junctions are promising candidates to improve the performance of graphene transistors that is usually hindered by the gapless nature of graphene. Although the energy bandgap of strained graphene still remains zero, the shift of Dirac points in the \textbf{\emph{k}}-space due to strain-induced deformation of graphene lattice can lead to the appearance of a finite conduction gap of several hundreds meV in strained junctions with a strain of only a few percent. However, s…
The transmission of the electron across the single normal metal-graphene (NG) and normal-metal-graphene-normal-metal (NGN) junctions has been investigated. For the single NG junction, the profile of the maximum transmission which has been plotted against the dimensionless interface hopping respectively bears similarity to that of the conductance of the system. The minor effect of the incidence energy on transmission can also be found in conductance of the single NG junction whose tunneling behavior poses a striking difference from that of the NGN junction. Concerning with NGN junction, the tra…
This paper is devoted to photocarrier transport across a two-dimensional graphene-semiconductor Schottky junction. We study linear response to monochromatic light with excitation energy well below the semiconductor band gap. The operation mechanism relies on both photoelectric and thermionic emission from graphene to a two-dimensional semiconductor under continuous illumination and zero bias. Due to the thermalization bottleneck for low-energy carriers in graphene, the photoelectric contribution is found to dominate the photoresponse at near-infrared excitation frequencies and below. The exten…
Electronic Whispering Gallery Modes (EWGMs) have been recently observed in several circular graphene junctions, pn and pp0, created in scanning tunnelling microscope experiments. By computing the local density of states within the Dirac-Weyl formalism for massless fermions we demonstrate that the EWGMs may really be emerged in any type of the electrostatic potential induced circular graphene junctions, including uni-junctions (e.g. np- or pp0-junctions) as well as bipolar-junctions (e.g. pnp-heterojunctions). Surprisingly, quantitative analyses show that for all the EWGMs identified (regardles…
We report on a method to fabricate and measure gateable molecular junctions which are stable at room temperature. The devices are made by depositing molecules inside a few-layer graphene nanogap, formed by feedback controlled electroburning. The gaps have separations on the order of 1-2 nm as estimated from a Simmons model for tunneling. The molecular junctions display gateable IV-characteristics at room temperature.
The interaction between doped graphene nanoislands connected by narrow junctions constitutes an ideal testbed to probe quantum effects in plasmonic systems. Here, the interaction between graphene plasmons in neighboring nanoislands is predicted to be extremely sensitive to the size and shape of the junctions. The reported {\it ab initio} calculations reveal three different regimes of interaction: (1) for narrow bridges ($<4$ carbon-atom rows), the conductance of the junction is too low to allow electron transport and the optical response is dominated by a characteristic bonding dipolar dimer m…
Josephson junctions with graphene as the weak link between superconductors have been intensely studied in recent years, with respect to both fundamental physics and potential applications. However, most of the previous work was based on mechanically exfoliated graphene, which is not compatible with mass production. Here we present our research using graphene grown by chemical vapour deposition (CVD) as the weak link of Josephson junctions. We demonstrate that CVD-graphene-based Josephson junctions with Nb electrodes can work effectively without any thermal hysteresis from 1.5 K down to a base …
In this study, we examine multiple encapsulated graphene Josephson junctions to determine which mechanisms may be responsible for the supercurrent observed in the quantum Hall (QH) regime. Rectangular junctions with various widths and lengths were studied to identify which parameters affect the occurrence of QH supercurrent. We also studied additional samples where the graphene region is extended beyond the contacts on one side, making that edge of the mesa significantly longer than the opposite edge. This is done in order to distinguish two potential mechanisms: a) supercurrents independently…
We report on low-temperature transport study of a single layer graphene (SLG)-twisted bilayer graphene (tBLG) junction device. The SLG-tBLG junction in the device is grown by chemical vapor deposition and the device is fabricated in a Hall-bar configuration on Si/SiO$_2$ substrate. The longitudinal resistances across the SLG-tBLG junction (cross-junction resistances) on the two sides of the Hall bar and the Hall resistances of SLG and tBLG in the device are measured. In the quantum Hall regime, the measurements show that the measured cross-junction resistances exhibit a series of new quantized…
Linear conductance of graphene-based p-n junctions with Rashba spin-orbit coupling is considered theoretically. A square potential step is used to model the junctions, while the coupling is introduced in terms of the Kane-Mele model (C.L. Kane and E.J. Mele, Phys.Rev.Lett. 95, 226801(2005)). The main objective is a description of electronic transport in junctions where Rashba parameter is nonuniform. Such a nonuniformity can appear when graphene is asymmetrically covered with atomic layers, or when Rashba coupling is strongly dependent on electric field. It is shown that conductance is signifi…
Ballistic transport in graphene p-n junctions in the presence of magnetic field exhibits two distinct regimes: At low fields, transport is partially suppressed by the field. When the field exceeds a certain critical value, the junction is pinched off by the Landau level formation. Transmission and conductance are found in the entire range of fields using Lorentz boost and mapping to the Landau-Zener problem. We show that perfect transmission occurs at a field-dependent collimation angle, indicating that the chiral dynamics of massless Dirac fermions persists at a finite magnetic field. A curre…
