Role of the charge inhomogeneity on the breakdown of the quantum Hall effect in narrow single layer graphene devices (original) (raw)
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Operation of graphene quantum Hall resistance standard in a cryogen-free table-top system
2D Materials, 2015
We demonstrate quantum Hall resistance measurements with metrological accuracy in a small cryogen-free system operating at a temperature of around 3.8 K and magnetic fields below 5 T. Operating this system requires little experimental knowledge or laboratory infrastructure, thereby greatly advancing the proliferation of primary quantum standards for precision electrical metrology. This significant advance in technology has come about as a result of the unique properties of epitaxial graphene on SiC.
Quantum resistance metrology in graphene
Applied Physics Letters, 2008
We have performed a metrological characterization of the quantum Hall resistance in a 1 µm wide graphene Hall-bar. The longitudinal resistivity in the center of the ν = ±2 quantum Hall plateaus vanishes within the measurement noise of 20 mΩ upto 2 µA. Our results show that the quantization of these plateaus is within the experimental uncertainty (15 ppm for 1.5 µA current) equal to that in conventional semiconductors. The principal limitation of the present experiments are the relatively high contact resistances in the quantum Hall regime, leading to a significantly increased noise across the voltage contacts and a heating of the sample when a high current is applied.
Local breakdown of the quantum Hall effect in narrow single layer graphene Hall devices
Solid State Communications, 2013
""We have analyzed the breakdown of the quantum Hall effect in 1 μm wide Hall devices fabricated from an exfoliated monolayer graphene transferred on SiOx. We have observed that the deviation of the Hall resistance from its quantized value is weakly dependent on the longitudinal resistivity up to current density of 5 A/m, where the Hall resistance remains quantized even when the longitudinal resistance increases monotonously with the current. Then a collapse in the quantized resistance occurs while longitudinal resistance keeps its gradual increase. The exponential increase of the conductivity with respect to the current suggests impurity mediated inter-Landau level scattering as the mechanism of the breakdown. The results are interpreted as the strong variation of the breakdown behavior throughout the sample due to the randomly distributed scattering centers that mediates the breakdown.""
A prototype of RK/200 quantum Hall array resistance standard on epitaxial graphene
Journal of Applied Physics, 2015
Epitaxial graphene on silicon carbide is a promising material for the next generation of quantum Hall resistance standards. Single Hall bars made of graphene have already surpassed their state-of-the-art GaAs based counterparts as an R K =2 (R K ¼ h=e 2 Þ standard, showing at least the same precision and higher breakdown current density. Compared to single devices, quantum Hall arrays using parallel or series connection of multiple Hall bars can offer resistance values spanning several orders of magnitude and (in case of parallel connection) significantly larger measurement currents, but impose strict requirements on uniformity of the material. To evaluate the quality of the available material, we have fabricated arrays of 100 Hall bars connected in parallel on epitaxial graphene. One out of four devices has shown quantized resistance that matched the correct value of R K =200 within the measurement precision of 10 À4 at magnetic fields between 7 and 9 T. The defective behaviour of other arrays is attributed mainly to non-uniform doping. This result confirms the acceptable quality of epitaxial graphene, pointing towards the feasibility of well above 90% yield of working Hall bars. V
2014
Replacing GaAs-based quantum Hall resistance standards (QHRS) by more convenient graphene based ones is still an ongoing goal in metrology. Although the required 10 −9 -precision has been reported in graphene based QHRS, these demonstrations were presented from a unique epitaxial graphene source and under high magnetic fields. A requirement to set graphene-based QHRS is the availability of other sources of graphene allowing the operation at lower magnetic fields. Here, we report on a 10 −9accurate quantized resistance over a 9 T range starting from 10 T on the ν = 2 plateau, at a temperature of 1.4 K, in a large Hall bar QHRS made of graphene grown by chemical vapor deposition (CVD) on SiC. The relative discrepancy between the quantized Hall resistances in the graphene sample and in a reference GaAs one is equal to (−2 ± 4) × 10 −10 . Using a current amplifier based on a superconducting quantum interference device to study the low dissipation in the QHE regime, we show that the physics of the Hall resistance plateau is characterized by a localization length of states at Fermi energy locked to the magnetic length over a large magnetic field range. This behavior is correlated with the structural properties of the CVD graphene. These results give a new proof of the universality of the QHE and constitute a further step towards a more convenient QHRS. They also demonstrate that CVD on SiC, a recently developed, hybrid and scalable growth technique, is now mature for applications.
Quantum Hall resistances of a multiterminal top-gated graphene device
Physical Review B, 2009
Four-terminal resistances, both longitudinal and diagonal, of a locally gated graphene device are measured in the quantum-Hall (QH) regime. In sharp distinction from previous two-terminal studies [J. R. Williams et al., Science 317, 638 (2007); B.Özyilmaz et al., Phys. Rev. Lett. 99, 166804 (2007)], asymmetric QH resistances are observed, which provide information on reflection as well as transmission of the QH edge states. Most quantized values of resistances are well analyzed by the assumption that all edge states are equally populated. Contrary to the expectation, however, a 5/2 transmission of the edge states is also found, which may be caused by incomplete mode mixing and/or by the presence of counter-propagating edge states. This four-terminal scheme can be conveniently used to study the edge-state equilibration in locally gated graphene devices as well as mono-and multi-layer graphene hybrid structures.
Towards a quantum resistance standard based on epitaxial graphene
Nature Nanotechnology, 2010
We report development of a quantum Hall resistance standard accurate to a few parts in a billion at 300 mK and based on large area epitaxial graphene. The remarkable precision constitutes an improvement of four orders of magnitude over the best results obtained in exfoliated graphene and is similar to the accuracy achieved in well-established semiconductor standards. Unlike the traditional resistance standards the novel graphene device is still accurately quantized at 4.2 K, vastly simplifying practical metrology. This breakthrough was made possible by exceptional graphene quality achieved with scalable silicon carbide technology on
Comparison Between Graphene and GaAs Quantized Hall Devices With a Dual Probe
IEEE Transactions on Instrumentation and Measurement, 2020
A graphene quantized Hall resistance (QHR) device fabricated at the National Institute of Standards and Technology (NIST) was measured alongside a GaAs QHR device fabricated by the National Research Council of Canada (NRC) by comparing them to a 1 kΩ standard resistor using a cryogenic current comparator. The two devices were mounted in a custom developed dual probe that was then assessed for its viability as a suitable apparatus for precision measurements. The charge carrier density of the graphene device exhibited controllable tunability when annealed after Cr(CO) 3 functionalization. These initial measurement results suggest that making resistance comparisons is possible with a single probe wired for two types of quantum standards-GaAs, the established material, and graphene, the newer material that may promote the development of more user-friendly equipment.
Epitaxial graphene for quantum resistance metrology
Metrologia
Graphene-based quantised Hall resistance standards promise high precision for the unit ohm under less exclusive measurement conditions, enabling the use of compact measurement systems. To meet the requirements of metrological applications, national metrology institutes developed large-area monolayer graphene growth methods for uniform material properties and optimized device fabrication techniques. Precision measurements of the quantised Hall resistance showing the advantage of graphene over GaAs-based resistance standards demonstrate the remarkable achievements realized by the research community. This work provides an overview over the state-of-the-art technologies in this field.