Quantum resistance metrology in graphene

Abstract

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. The Hall resistance in two-dimensional electron systems (2DESs) is quantized in terms of natural constants only, R H = h/ie 2 with i an integer number [1]. Due to its high accuracy and reproducibility this quantized Hall resistance in conventional 2DESs is nowadays used as a universal resistance standard [2].Recently a new type of half-integer quantum Hall effect [3,4] was found in graphene, the purely twodimensional form of carbon [5]. Its unique electronic properties [6] (mimicking the behavior of charged chiral Dirac fermions [7,8]) allow the observation of a quantized Hall resistance up to room-temperature [9, 10], making graphene a promising candidate for a high-temperature quantum resistance standard. Although the quantized resistance in graphene around the ν = 2 plateau is generally believed to be equal to h/2e 2 , up to now it has not been shown to meet a metrological standard. In this Letter we present results of the first metrological characterization of the quantum Hall resistance in graphene. In particular, we will address the present accuracy of quantization (15 ppm) and the experimental conditions limiting this accuracy.Our sample consists of a graphene Hall-bar on a Si/SiO 2 substrate forming a charge-tunable ambipolar field-effect transistor (A-FET), where the carrier concentration can be tuned with a back-gate voltage V g [11]. In order to remove most of the surface dopants that make graphene generally strongly hole doped and limit its mobility, we have annealed the sample in-situ for several hours at 380 K prior to cooling it down slowly (∆T /∆t < 3 K/min) to the base temperature (0.35 K) of a toploading 3 He-system equipped with a 15 T superconducting magnet. After annealing, the charge neutrality point in the A-FET was situated at 5 V and the sample dis- * Electronic address: J.Giesbers@science.ru.nl † Electronic address: U.Zeitler@science.ru.nl 2 µm

Nonlinear screening of charges induced in graphene by metal contacts

“…The latter has been recently observed by scanning photocurrent microscopy, 8 and might also be seen for graphene in the quantum Hall regime. 24,33 The contact effects also result in the formation of a p-p , n-n or p-n junction at the near contact area that breaks the electron-hole symmetry and contributes to the contact resistance.…”

Unconventional Correlation between Quantum Hall Transport Quantization and Bulk State Filling in Gated Graphene Devices

“…Achieving high accuracy of QH resistance quantization requires minimization of dissipation, favoring wide incompressible regions. Our results suggest that the edge carrier profile should be carefully considered when gated graphene devices are used for such purpose [31] because it can alter the configuration of incompressible regions at QH plateaux. 3) Transport-based analysis of localization during the transition between LL plateaux may need to be revisited since the evolution of the bulk state during the transition is different from the conventional assumption.…”

Preparation and characterisation of exfoliated graphene for quantum resistance metrology

“…van Elferen (2) , A.J.M. Giesbers (2) , A. Veligura (4) , U. Zeitler (2) , K.S. Novoselov (3) , B.J.…”