We investigate phase-coherent transport and show Aharonov-Bohm (AB) oscillations in quasiballistic graphene rings with hard confinement. Aharonov-Bohm oscillations are observed in a graphene quantum ring with a topgate covering one arm of the ring. As graphene is a gapless semiconductor, this. Graphene rings in magnetic fields: Aharonov–Bohm effect and valley splitting. J Wurm1,2, M Wimmer1, H U Baranger2 and K Richter1. Published 3 February.

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B 76 Crossref. Inset illustrates the trajectory of charge carriers inside a conductance plateau.

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Figure 6 a Schematic illustration of a ring with a charge puddle connecting the inner and outer edge channel in the quantum Hall regime. On the other hand, the electric field may change the electron density and thereby the Fermi wavelength of the carriers. Values are normalized with respect to the conductance at zero B field and an offset is added for clarity. The density change is related via a parallel plate capacitor model to a change in back gate voltage, i. This makes it possible to use external gates for locally tuning the density and the Fermi wave vector in one of the arms and therefore allows us to observe the electrostatic Aharonov—Bohm effect without the use of tunnel barriers in the arms of the ring.

Aharonov Y and Bohm D Phys. Therefore, the presented measurements are all close to the diffusive dirty metal regime, and carrier scattering at the sample boundaries alone cannot fully account for the value of the mean free path.

Figure 1 aharronov Scanning force microscopy image of device 1 with a schematic of the measurement configuration. We therefore believe that the smaller ring dimensions in combination with the four-terminal arrangement may be responsible for the larger value of the visibility observed in our experiment. For b the background resistance has been subtracted as described in the text.


The data are analyzed by a simple dirty metal model justified by a comparison of the different length ahagonov characterizing the system. The measured resistance is composed of the ring resistance itself and the resistance of the graphene leads. This indicates that thermal averaging ahaeonov interference contributions to the conductance is expected to be relevant. Sign up for new issue notifications. Red dashed lines shows G 2 W used for background subtraction.

We therefore speculate that the paths contributing to transport, in general, and to the Aharonov—Bohm effect, in particular, may not cover the entire geometric area of the ring arms. The width of this peak is significantly smaller than the range of frequencies expected from the haaronov of possible enclosed areas in our geometry indicated as a gray-shaded region in figure 2 c.

The observed data can be interpreted within existing models for ‘dirty metals’. In panel c the traces are plotted with an offset for clarity. ahsronov

[] The Aharonov-Bohm effect in graphene rings

Series I Physics Physique Fizika. The conductance for the disk is shown for different strength of edge roughness with the result that the position of the conductance minima are rather robust to edge roughness. The amplitude of the Aharonov—Bohm oscillations is modulated as graphhene function of magnetic field on the same scale as the background resistance, indicating that a finite number of paths enclosing a range of different areas contribute to the oscillations.

In general, the observed Aharonov—Bohm oscillations become more pronounced for smaller current levels, as expected. In a semiclassical Drude picture, these resistances can be calculated from the geometric aspect ratios i.

[] Aharonov-Bohm oscillations and magnetic focusing in ballistic graphene rings

Moreover we show signatures of magnetic ahatonov effects at small magnetic fields confirming ballistic transport. Closer inspection shows that the antisymmetric part in the magnetic field of each trace not shown is more than a factor of 10 smaller than the symmetric part. It works to advance physics research, application and education; and engages with policy makers and the public to develop awareness and understanding of physics.


Ferrari A C et al Phys.

Condensed Matter > Mesoscale and Nanoscale Physics

However, trying to relate the visibilities observed in the two experiments quantitatively assuming that all experimental parameters except the ring radius are the same would lead to a phase-coherence length l smaller than the ring circumference L and only slightly larger than the ring radius r 0.

The lower panel shows the semiclassically calculated transmission through the ring for more details see text. The B -field axis is divided into three regimes: Aaronov measured resistance R meas consists of the following parts: Abstract We present low-temperature magnetotransport measurements on graphene rings encapsulated in hexagonal boron nitride. Figure 4 a Schematic representation of the different ring geometries of samples 1 and 2.

In this work, we have studied the Aharonov—Bohm effect in graphene in a two-terminal ring, but using graphdne four-contact geometry. We discuss the latter effect in more detail below, since the relative change in the Fermi wavelength is expected to be more pronounced in graphene compared to conventional metals.

We present low-temperature magnetotransport measurements on graphene rings encapsulated in hexagonal boron nitride.