Anomalously strong pinning of the filling factorν=2in epitaxial graphene

Abstract

We explore the robust quantization of the Hall resistance in epitaxial graphene grown on Siterminated SiC. Uniquely to this system, the dominance of quantum over classical capacitance in the charge transfer between the substrate and graphene is such that Landau levels (in particular, the one at exactly zero energy) remain completely filled over an extraordinarily broad range of magnetic fields. One important implication of this pinning of the filling factor is that the system can sustain a very high nondissipative current. This makes epitaxial graphene ideally suited for quantum resistance metrology, and we have achieved a precision of 3 parts in 10 10 in the Hall resistance quantization measurements. Graphene is believed to offer an excellent platform for QHE metrology due to the large energy separation between Landau levels (LL) resulting from the Dirac-type "massless" electrons specific for its band structure [12]. The Hall resistance quantization with an accuracy of 3 parts in 10 9 has already been established [7] in Hall-bar devices manufactured from epitaxial graphene grown on Si-terminated face of SiC (SiC/G). However, for graphene to be practically employed as an embodiment of a quantum resistance standard, it needs to satisfy further stringent requirements [11], in particular with respect to robustness over a range of temperature, magnetic field and measurement current. A high measurement current, which a device can sustain at a given temperature without dissipation, is particularly important for precision metrology as it defines the maximum attainable signalto-noise ratio.The extent of the QHE plateaux in conventional 2D electron systems is, usually, set by disorder and temperature. Disorder pins the Fermi energy in the mobility gap of the 2D system, which suppresses dissipative transport at low temperatures over a finite range of magnetic fields around the values corresponding to exactly filled LLs. These values can be calculated from the carrier density n s determined from the low-field Hall resistivity measurements and coincide with the maximum non-dissipative current, the breakdown current. Thus, the breakdown current in conventional two-dimensional semicondutors peaks very close to the field values where the filling factor ν is an even integer [11]. Though less studied experimentally, the behaviour of the breakdown current on the plateaux for the exfoliated graphene, including the ν = 2 plateau corresponding to the topologically protected N = 0 LL, looks quite similar [13].In this Brief Report we explore the robustness of the Hall resistance quantization in SiC/G. Unlike the QHE in conventional 2D systems, where the carrier density is independent of magnetic field, here specifically to SiC/G, we find that the carrier density in graphene varies with magnetic field due to the charge transfer between surface donor states in SiC and graphene. Most importantly, we find magnetic field intervals of several Tesla, where the carrier density in graphene increases linearly with the magnetic field, resulting ...

Towards a graphene-based quantum impedance standard

“…A second remarkable difference is that the graphene plateau is much wider than in GaAs devices. This was first observed by Janssen et al [20] in dc QHR measurements and is explained by charge transfer between the substrate and the epitaxial graphene pinning the filling factor over a wide range of magnetic flux density.…”

“…From the slope of the Hall resistance at low magnetic flux densities (see the dashed line in Fig. 2), the electron concentration of the device was determined as n = 6.3×10 11 cm -2 , predicting ν = 2 at around B = 13 T (disregarding the fact that the ν = 2 state continues to much higher magnetic flux densities due to the Fermi level pinning effect reported in [20]). The electron mobility of µ = 1730 cm 2 /Vs was determined from n and R xx at zero magnetic field.…”

Nonequilibrium mesoscopic conductance fluctuations as the origin of 1/f noise in epitaxial graphene

“…In epitaxial graphene, surface-donor states in the underlying SiC substrate act as a charge reservoir in proximity to the two-dimensional electron gas [65,66]. In strong magnetic fields, the carrier concentration of epitaxial graphene varies with the magnetic flux density due to a charge transfer between the surface-donor states and the graphene.…”

Weak localization scattering lengths in epitaxial, and CVD graphene

“…The fittings are used to demonstrate the validity of this method for devices with carrier densities ranging from 1 × 10 11 cm −2 to 1.43 × 10 13 cm −2 . Devices are analyzed from graphene produced by epitaxial growth on SiC 7 and chemical vapor deposition (CVD) onto thin metal films. 8 The results are compared with those obtained from the literature [9][10][11][12] and together are used to measure trends in the scattering lengths with carrier density.…”