Electronic transport properties of a tilted graphenep−njunction (original) (raw)
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Quantum Hall Effect in a Gate-Controlled p-n Junction of Graphene
Science, 2007
The unique band structure of graphene allows reconfigurable electric-field control of carrier type and density, making graphene an ideal candidate for bipolar nanoelectronics. We report the realization of a single-layer graphene p-n junction in which carrier type and density in two adjacent regions are locally controlled by electrostatic gating. Transport measurements in the quantum Hall regime reveal new plateaus of two-terminal conductance across the junction at 1 and 3 /2 times the quantum of conductance, e 2 /h, consistent with recent theory. Beyond enabling investigations in condensed-matter physics, the demonstrated local-gating technique sets the foundation for a future graphene-based bipolar technology.
Valley-isospin dependence of the quantum Hall effect in a graphene p-n junction
Physical Review B, 2007
We calculate the conductance G of a bipolar junction in a graphene nanoribbon, in the highmagnetic field regime where the Hall conductance in the p-doped and n-doped regions is 2e 2 /h. In the absence of intervalley scattering, the result G = (e 2 /h)(1 − cos Φ) depends only on the angle Φ between the valley isospins (= Bloch vectors representing the spinor of the valley polarization) at the two opposite edges. This plateau in the conductance versus Fermi energy is insensitive to electrostatic disorder, while it is destabilized by the dispersionless edge state which may exist at a zigzag boundary. A strain-induced vector potential shifts the conductance plateau up or down by rotating the valley isospin.
Semiclassical magnetotransport in graphene n-p junctions
Physical Review B, 2011
We provide a semiclassical description of the electronic transport through graphene n-p junctions in the quantum Hall regime. This framework is known to experimentally exhibit conductance plateaus whose origin is still not fully understood. In the magnetic regime (E < vF B), we show the conductance of excited states is essentially zero, while that of the ground state depends on the boundary conditions considered at the edge of the sample. In the electric regime (E > vF B), for a step-like electrostatic potential (abrupt on the scale of the magnetic length), we derive a semiclassical approximation for the conductance in terms of the various snake-like trajectories at the interface of the junction. For a symmetric configuration, the general result can be recovered using a simple scattering approach, providing a transparent analysis of the problem under study. We thoroughly discuss the semiclassical predicted behavior for the conductance and conclude that any approach using fully phase-coherent electrons will hardly account for the experimentally observed plateaus.
Manifestation of chiral tunneling at a tilted graphene pn junction
2012
Electrons in graphene follow unconventional trajectories at PN junctions, driven by their pseudospintronic degree of freedom. Significant is the prominent angular dependence of transmission, capturing the chiral nature of the electrons and culminating in unit transmission at normal incidence (Klein tunneling). We theoretically show that such chiral tunneling can be directly observed from the junction resistance of a tilted interface probed with separate split gates. The junction resistance is shown to increase with tilt in agreement with recent experimental evidence. The tilt dependence arises because of the misalignment between modal density and the anisotropic transmission lobe oriented perpendicular to the tilt. A critical determinant is the presence of edge scattering events that can completely reverse the angle-dependence. The absence of such reversals in the experiments indicates that these edge effects are not overwhelmingly deleterious, making the premise of transport governed by electron 'optics' in graphene an exciting possibility.
Graphene n-p junction in a strong magnetic field: A semiclassical study
Physical Review B, 2010
We provide a semiclassical description of the electronic transport through graphene n-p junctions in the quantum Hall regime. A semiclassical approximation for the conductance is derived in terms of the various snake-like trajectories at the interface of the junction. For a symmetric (ambipolar) configuration, the general result can be recovered by means of a simple scattering approach, providing a very transparent qualitative description of the problem under study. Consequences of our findings for the understanding of recent experiments are discussed.
Electrical transport in high-quality graphene pnp junctions
New Journal of Physics, 2009
We fabricate and investigate high quality graphene devices with contactless, suspended top gates, and demonstrate formation of graphene pnp junctions with tunable polarity and doping levels. The device resistance displays distinct oscillations in the npn regime, arising from the Fabry-Perot interference of holes between the two pn interfaces. At high magnetic fields, we observe well-defined quantum Hall plateaus, which can be satisfactorily fit to theoretical calculations based on the aspect ratio of the device. Graphene 1-3 is a two dimensional allotrope of carbon with a unique linear dispersion relation for low-lying excitations. Its gapless electronic band structure allows continuous tuning of charge carrier type and density by an electrostatic gate. Thus, one of the unique device configurations enabled by graphene is a dual-gated device, in which two or more gates are used to individually control charge density in different regions, realizing, for instance, pnp or npn junctions with in situ tunable junction polarity and doping levels 4-6 . Such pnp junctions have been demonstrated experimentally 7-14 , offering unique platforms for investigation of novel phenomena such as Klein tunneling 15, 16 , particle collimation 4, 17 , anisotropic transmission 18 and Veselago lensing effects 19 .
Spin-orbit effects in a graphene bipolar pn junction
EPL (Europhysics Letters), 2009
PACS 73.23-b-Electronic transport in mesoscopic systems PACS 76.63.-b-Electronic transport in nanoscale materials and structures PACS 73.40.-c-Electronic transport in interface structures Abstract.-A graphene pn junction is studied theoretically in the presence of both intrinsic and Rashba spin-orbit couplings. We show that a crossover from perfect reflection to perfect transmission is achieved at normal incidence by tuning the perpendicular electric field. By further studying angular dependent transmission, we demonstrate that perfect reflection at normal incidence can be clearly distinguished from trivial band gap effects. We also investigate how spin-orbit effects modify the conductance and the Fano factor associated with a potential step in both nn and np cases.
Physical Review B, 2016
We report distinctive magnetotransport properties of a graphene p-n-p junction prepared by controlled diffusion of metallic contacts. In most cases, materials deposited on a graphene surface introduce substantial carrier scattering, which greatly reduces the high mobility of intrinsic graphene. However, we show that an oxide layer only weakly perturbs the carrier transport, which enables fabrication of a high-quality graphene p-n-p junction through a one-step and resist-free method. The measured conductance-gate voltage (−) curves can be well described by a metal contact model, which confirms the charge density depinning due to the oxide layer. The graphene p-n-p junction samples exhibit pronounced quantum Hall effect, a well-defined transition point of the zeroth Landau level (LL), and scaling behavior. The scaling exponent obtained from the evolution of the zeroth LL width as a function of temperature exhibits a relatively low value of κ = 0.21 ± 0.01. Moreover, we calculate the energy level for the LLs based on the distribution of plateauplateau transition points, further validating the assignment of the LL index of the QH plateau-plateau transition.
Quenching of the Quantum Hall Effect in Graphene with Scrolled Edges
Physical Review Letters, 2012
Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arc length of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short-circuit the bulk current paths and inhibit the observation of the quantized twoterminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size. PACS numbers: 72.80.Vp,73.22.Pr