Quantum Hall Effect and Quantum Point Contact in Bilayer-Patched Epitaxial Graphene (original) (raw)

Quantum Hall Effect in a Gate-Controlled p-n Junction of Graphene

Science, 2007

The unique band structure of graphene allows reconfigurable electric-field control of carrier type and density, making graphene an ideal candidate for bipolar nanoelectronics. We report the realization of a single-layer graphene p-n junction in which carrier type and density in two adjacent regions are locally controlled by electrostatic gating. Transport measurements in the quantum Hall regime reveal new plateaus of two-terminal conductance across the junction at 1 and 3 /2 times the quantum of conductance, e 2 /h, consistent with recent theory. Beyond enabling investigations in condensed-matter physics, the demonstrated local-gating technique sets the foundation for a future graphene-based bipolar technology.

Experimental evidence for direct insulator-quantum Hall transition in multi-layer graphene

We have performed magnetotransport measurements on a multi-layer graphene flake. At the crossing magnetic field B c , an approximately temperature-independent point in the measured longitudinal resistivity ρ xx , which is ascribed to the direct insulator-quantum Hall (I-QH) transition, is observed. By analyzing the amplitudes of the magnetoresistivity oscillations, we are able to measure the quantum mobility μ q of our device. It is found that at the direct I-QH transition, μ q B c ≈ 0.37 which is considerably smaller than 1. In contrast, at B c , ρ xx is close to the Hall resistivity ρ xy , i.e., the classical mobility μB c is ≈ 1. Therefore, our results suggest that different mobilities need to be introduced for the direct I-QH transition observed in multi-layered graphene. Combined with existing experimental results obtained in various material systems, our data obtained on graphene suggest that the direct I-QH transition is a universal effect in 2D.

Gate-Defined Graphene Quantum Point Contact in the Quantum Hall Regime

Physical Review Letters, 2011

We investigate transport in a gate-defined graphene quantum point contact in the quantum Hall regime. Edge states confined to the interface of p and n regions in the graphene sheet are controllably brought together from opposite sides of the sample and allowed to mix in this split-gate geometry. Among the expected quantum Hall features, an unexpected additional plateau at 0.5 h/e 2 is observed. We propose that chaotic mixing of edge channels gives rise to the extra plateau.

Quantum Hall conductance of two-terminal graphene devices

Physical Review B, 2009

Measurement and theory of the two-terminal conductance of monolayer and bilayer graphene in the quantum Hall regime are compared. We examine features of conductance as a function of gate voltage that allow monolayer, bilayer, and gapped samples to be distinguished, including N-shaped distortions of quantum Hall plateaus and conductance peaks and dips at the charge neutrality point. Generally good agreement is found between measurement and theory. Possible origins of discrepancies are discussed.

Two-dimensional ferromagnetism detected by proximity-coupled quantum Hall effect of graphene

npj Quantum Materials, 2022

The recent discovery of a two-dimensional van der Waals magnet has paved the way for an enhanced understanding of two-dimensional magnetic systems. The development of appropriate heterostructures in this emerging class of materials is required as the next step towards applications. Here, we report on the electrical transport in monolayer graphene coupled with the two-dimensional ferromagnet Cr2Ge2Te6 (CGT). Graphene that forms an interface with CGT is electron-doped owing to charge transfer. The temperature-dependent resistance of graphene/CGT undergoes a nontrivial sudden change near the Curie temperature (Tc) of CGT. Apart from this, the behavior of various transport parameters also differs before and after Tc. Moreover, the contribution of the magnetization of CGT to the enhanced magnetic flux density leads to the critical evolution of the quantum Hall state. These results imply that graphene in the graphene/CGT hybrid structure can be utilized to electrically monitor the magneti...

Manipulating quantum Hall edge channels in graphene through scanning gate microscopy

Physical Review B

We show evidence of the backscattering of quantum Hall edge channels in a narrow graphene Hall bar, induced by the gating effect of the conducting tip of a Scanning Gate Microscope, which we can position with nanometer precision. We show full control over the edge channels and are able, due to the spatial variation of the tip potential, to separate co-propagating edge channels in the Hall bar, creating junctions between regions of different charge carrier density, that have not been observed in devices based on top-or split-gates. The solution of the corresponding quantum scattering problem is presented to substantiate these results, and possible follow-up experiments are discussed.

Mapping quantum Hall edge states in graphene by scanning tunneling microscopy

Physical Review B

Quantum Hall edge states are the paradigmatic example of bulk-boundary correspondence. They are prone to intricate reconstructions calling for their detailed investigation at high spatial resolution. Here, we map quantum Hall edge states of monolayer graphene at a magnetic field of 7 T with scanning tunneling microscopy. Our graphene sample features a gate-tunable lateral interface between areas of different filling factor. We compare the results with detailed tight-binding calculations, quantitatively accounting for the perturbation by the tip-induced quantum dot. We find that an adequate choice of gate voltage allows for mapping the edge state pattern with little perturbation. We observe extended compressible regions, the antinodal structure of edge states, and their meandering along the lateral interface.

AC Quantum Hall Effect in Epitaxial Graphene

IEEE Transactions on Instrumentation and Measurement, 2017

This paper describes the measurements of the ac quantum Hall effect (QHE) in epitaxial graphene in a set of six different devices. In typical graphene devices, capacitive losses cause a negative frequency dependence of the quantum Hall resistance, in contrast to the positive frequency dependence observed in GaAs devices. In one sample, very low ac dissipation was measured along with a quantum Hall resistance decreasing by less than one part in 10 7 between 0 and 10 kHz, which demonstrates the potential of the QHE in graphene samples to be used as a primary standard of impedance.