Observation Of Quantum Hall Effect Research Articles

Spontaneous doping on high quality talc-graphene-hBN van der Waals heterostructures

Steady doping, added to its remarkable electronic properties, would make graphene a valuable commodity in the solar cell market, as energy power conversion could be substantially increased. Here we report a graphene van der Waals heterostructure which is able to spontaneously dope graphene (p-type) up to n ~ 2.2 × 1013 cm−2 while providing excellent charge mobility ( ~ 25 000 cm2 V−1 s−1). Such properties are achieved via deposition of graphene on atomically flat layered talc, a natural and abundant dielectric crystal. Raman investigation shows a preferential charge accumulation on graphene-talc van der Waals heterostructures, which are investigated through the electronic properties of talc/graphene/hBN heterostructure devices. These heterostructures preserve graphene’s good electronic quality, verified by the observation of quantum Hall effect at low magnetic fields (B = 0.4 T) at T = 4.2 K. In order to investigate the physical mechanisms behind graphene-on-talc p-type doping, we performed first-principles calculations of their interface structural and electronic properties. In addition to potentially improving solar cell efficiency, graphene doping via van der Waals stacking is also a promising route towards controlling the band gap opening in bilayer graphene, promoting a steady n or p type doping in graphene and, eventually, providing a new path to access superconducting states in graphene, predicted to exist only at very high doping.

Observation of Quantum Hall effect in an ultra-thin (Bi0.53Sb0.47)2Te3 film

We report the observation of the Quantum Hall effect from the topological surface states in both the Dirac electron and Dirac hole regions in a 4 quintuple layer (Bi0.53Sb0.47)2Te3 film grown on GaAs (111)B substrates. The Fermi level is sitting within the enlarged bulk band gap due to the quantum confinement of the ultra-thin film and can be tuned through the Dirac point by gate biases. Furthermore, the Hall resistance Rxy shows even denominator plateaus, which could be fractional Quantum Hall states. This may be due to the hybridization between the top and bottom surface states and suggests the possible way to manipulate the interaction of two surfaces for potential spintronic devices.

Observation of quantum Hall effect in a microstrained Bi2Se3 single crystal

We report the observation of quantum Hall effect (QHE) in a Bi2Se3 single crystal having carrier concentration (n)∼1.13×1019cm−3, three dimensional Fermi surface and bulk transport characteristics. The plateaus in Hall resistivity coincide with minima of Shubnikov de Haas oscillations in resistivity. Our results demonstrate that the presence of perfect two dimensional transport is not an essential condition for QHE in Bi2Se3. The results of high resolution X-ray diffraction (HRXRD), energy-dispersive X-ray spectroscopy (EDX), and residual resistivity measurements show the presence of enhanced crystalline defects and microstrain. We discuss the possible origin of the observed QHE and correlate its existence to the crystalline defects.

Observation of Quantum Hall Effect and weak localization in p-type bilayer epitaxial graphene on SiC(0001)

We investigated the magnetotransport properties of a bilayer graphene Hall bar sample epitaxially grown on Si-terminated silicon carbide. Integer quantum Hall effect and weak localization effect were observed. From the weak localization effect, the carrier scattering and phase coherence were extracted. The extracted phase coherence length is 0.5μm at 2K, which is comparable with that of the exfoliated graphene. The temperature dependence of the phase coherence rate shows that electron–electron interaction is the main inelastic-scattering factor and direct Coulomb interaction also exists. Compared with exfoliated bilayer graphene, no sign of weak antilocalization was observed at such high carrier concentration of 1013cm−2 due to the strong intervally scattering. Both the strong intervally scattering and Coulomb interaction of phase coherence are due to the large amount of atomically sharp defects in epitaxial graphene on Si-terminated SiC.

Observation of quantum Hall effect in mono- and bi-layer graphene using pulse magnet

We report on the magnetotransport measurements of mono- and bi-layer graphene in pulsed high magnetic fields up to B = 53 T. In a mono-layer graphene, the Hall resistance RH is quantized to RH = (h/e2)ν−1 with ν = 2, 6, and 10 for either hole or electron doping. In a bi-layer graphene, RH is quantized to RH = (h/e2)ν−1 with ν = 4, 8, and 12. These results indicate that the precise magnetotransport measurements of the graphene can be conducted in the environment of pulse magnetic fields.

The experimental observation of quantum Hall effect of l=3 chiral quasiparticles in trilayer graphene

Low-energy electronic states in monolayer and bilayer graphenes present chiral charge carriers with unique and unusual properties of interest for electronic applications. Here, we report the magnetotransport measurements in the ABC-stacked trilayer graphene as a function of charge carrier density, magnetic field, and temperature, which show clear evidence of l = 3 chiral quasiparticles with cubic dispersion, existing in a large, 20x60 sq. microns device. Shubnikov-deHaas oscillations (SdHO) reveal the Berry's phase 3\pi, and the marked increase of cyclotron mass near charge neutrality, consistent with divergent behavior expected for l = 3 quasiparticles. We also observe the predicted unconventional sequence of quantum Hall effect (QHE) plateaus, +/-6e^2/h, +/-10e^2/h, ... .

Electrical measurement of non-destructively p-type doped graphene using molybdenum trioxide

We demonstrate effective non-destructive p-type doping of graphene via surface modification with molybdenum trioxide (MoO3) thin film using electrical transport measurements. The p-type doping via MoO3 modification of graphene leads to the downward shift of Fermi level towards the valence band. MoO3 modified graphene retains its high charge carrier mobility, facilitating the observation of quantum Hall effect. In-situ ultraviolet photoelectron spectroscopy studies also show that air exposure of MoO3 modified graphene reduces the doping efficiency.

Observation of quantum-Hall effect in gated epitaxial graphene grown on SiC (0001)

Epitaxial graphene films examined were formed on the Si-face of semi-insulating 4H-SiC substrates by a high temperature sublimation process. A high-k gate stack on the epitaxial graphene was realized by inserting a fully oxidized nanometer thin aluminum film as a seeding layer, followed by an atomic-layer deposition process. The electrical properties of epitaxial graphene films are retained after gate stack formation without significant degradation. At low temperatures, the quantum-Hall effect in Hall resistance is observed along with pronounced Shubnikov–de Haas oscillations in diagonal magnetoresistance of gated epitaxial graphene on SiC (0001).

ＺｎＯヘテロ接合の表面・界面制御と量子伝導

We have observed the quantum Hall-effect (QHE) of ZnO/MgxZn1−xO bilayers grown on ScAlMgO4 substrates by using pulsed-laser deposition. Two-dimensional electron gas was spontaneously formed in the interface due to the polarization mismatch between the layers. In order to obtain high electron mobility, we first developed a high-temperature annealed buffer layer, and then carefully investigated the growth temperature dependences of surface morphologies and electrical properties. As the result, electron mobility was recorded to be 440 cm2/Vs at room temperature and 5500 cm2/Vs at 1 K. The observation of QHE allows to access direct determination of the electronic structure of the heterointerface.

First observation of quantum Hall effect in a GaInAsP-InP heterostructure grown by metalorganic vapor deposition

We report the first observation of quantum Hall effect in a Ga0.25In0.75As0.5P0.5 heterostructure grown by metalorganic chemical vapor deposition growth technique.

Observation of quantum hall effect in Si-MOSFET's by means of conventional and Josephson potentiometer systems

Measurements of the quantized Hall resistance <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> ), <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> =4, 8, and 12, have been made for silicon metal-oxide semiconductor field-effect transistors under different experimental conditions <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> =0.5 to 1.4K and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> =10.5 to 14 T, using conventional potentiometer and galvanometer systems. These values of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> (4) are in agreement with those obtained by means of a preliminary system of Josephson potentiometer and SQUID galvanometer to within a few parts in 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> .