Conductance quantization suppression in the quantum Hall regime

Abstract

Conductance quantization is the quintessential feature of electronic transport in non-interacting mesoscopic systems. This phenomenon is observed in quasi one-dimensional conductors at zero magnetic field B, and the formation of edge states at finite magnetic fields results in wider conductance plateaus within the quantum Hall regime. Electrostatic interactions can change this picture qualitatively. At finite B, screening mechanisms in narrow, gated ballistic conductors are predicted to give rise to an increase in conductance and a suppression of quantization due to the appearance of additional conduction channels. Despite being a universal effect, this regime has proven experimentally elusive because of difficulties in realizing one-dimensional systems with sufficiently hard-walled, disorder-free confinement. Here, we experimentally demonstrate the suppression of conductance quantization within the quantum Hall regime for graphene nanoconstrictions with low edge roughness. Our findings may have profound impact on fundamental studies of quantum transport in finite-size, two-dimensional crystals with low disorder.

Quantized Electron Transport Through Graphene Nanoconstrictions

“…We have fabricated GNCs by EBL of mechanical exfoliated graphene flakes transferred to Si/SiO 2 wafers treated before and after the exfoliation with hexamethyldisilazane (HMDS), following a similar procedure to the one used by Caridad et al It is expected that graphene deposited on a hydrophobic substrate has better transport properties due to the HMDS immersion. In particular, these samples show higher carrier mobility and Dirac peaks closer to zero due to the low interaction of graphene with the substrate …”

Oxidation of Suspended Graphene: Etch Dynamics and Stability Beyond 1000 °C

“…1,2 Edge roughness in particular is critical to device performance as devices approach ballistic limits, 3 and changing the edge roughness can lead to suppression of carrier mobility, 4,5 thermal conductivity, 6,7 or a complete change in the physics of a device: for example the recently demonstrated suppression of quantization in the quantum Hall effect in narrow graphene constrictions with smooth edges. 3 As argued by Geim and Novoselov, graphene nanoribbons with widths of about 10 nm are needed to obtain technologically relevant band gaps at room temperature. 8 While such small dimensions no longer present a significant hurdle for modern lithographic technologies, 9 the true bottleneck is now in defining structures in graphene with a sufficiently controlled crystallographic orientation and degree of edge roughness.…”

Fabrication and characterization of Quantum Materials: Graphene heterostructures and Topological Insulators

“…This result, supported by the remarkable agreement with theoretical calculations using realistic profiles of the edge roughness, is a clear indication of ballistic transport due to the very high mobility and smooth edges that arise from the novel use of the cryo-etching procedure in their preparation. The estimated value of t in our structure is also significantly higher than the one obtained in much narrower NCs of width W = 100 nm produced by means of a HMDS treatment [100,101] and reported in the previous section. In these samples, low-roughness edges are generated mainly due to the fact that the etching process on a single layer graphene is more controllable and a clean edge on a single layer of material is easier to attain than the one obtained on a thicker encapsulated graphene nanostructure.…”

“…We have fabricated GNCs [100] through electron beam litography of mechanical exfoliated graphene flakes transferred to Si/SiO2 wafers treated before and after the exfoliation with hexamethyldisilazane, following a similar procedure to the one used by Caridad et al [101]. Details on the fabrication process can be found in section 3.1.1.…”