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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The density change is related via a parallel plate capacitor model to a change in back gate voltage, i. Red dashed lines shows G 2 W used for background subtraction. The Deutsche Physikalische Gesellschaft DPG with a tradition extending back to is the largest physical society in the world with more than 61, members. B 75 Crossref. We investigate the magnetoresistance of a side-gated ring structure etched out of single-layer graphene.

The measured resistance R meas consists of the following parts: Figure 6 a Schematic illustration of a ring with a charge puddle connecting the inner and outer edge channel in aharohov quantum Hall regime. Frequency range of individual AB oscillation modes marked by arrows. 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 ahqronov ring arms.

Red box indicates the selected B -field region.

B 76 Crossref. Figure 4 a Schematic representation of the different ring geometries of samples 1 and 2. The B -field axis is divided into three regimes: The DPG sees itself as the forum and mouthpiece for physics and is a non-profit organisation that does not pursue financial interests. Electron beam lithography followed by reactive ion etching is used to define the structure.


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The Aharonov–Bohm effect in a side-gated graphene ring

These oscillations are well explained by taking disorder into account allowing for a coexistence of hard- and soft-wall confinement. One possible interpretation is that the sample has rough unordered edges leading to a region along the edges that does not contribute to the electrical transport.

B 40 Crossref. The amplitude of the Aharonov—Bohm oscillations is modulated as a function of magnetic field on the same scale as the background resistance, indicating that a finite haaronov of paths enclosing a range of different areas contribute to the oscillations.

We remark here that this assumption, and the reasoning based on it as given in the main text, corresponds to the usual argument made for dirty metals. The measured resistance is composed of the ring resistance itself and the resistance of the graphene leads.

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

A magnetic field is applied perpendicular to the sample plane. In this work, we have studied the Aharonov—Bohm effect in graphene in a two-terminal ring, but using a four-contact geometry. Zoom In Zoom Out Reset image size. For aharoonv the background resistance has been subtracted as described in the text. We also note that the diffusive regime investigated in our device is quite extended in abaronov gate voltage. 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.

While the earlier research interests were focused on the most basic nanostructures, e. The inset highlights cycloid drift motion of an edge channel along the charge puddle.

Therefore measurements presented here were taken over only small ranges of back gate voltage aharonv having allowed the sample to stabilize in this range.


On the other hand, the electric field may change the electron density and thereby the Fermi wavelength of the carriers. In a semiclassical Drude picture, these resistances can be calculated from the geometric aspect ratios i.

[] The Aharonov-Bohm effect in graphene rings

We present low-temperature magnetotransport measurements on graphene rings encapsulated in hexagonal boron nitride. The inset shows a close-up of the FFT spectrum.

The lower panel shows the semiclassically calculated transmission through the ring for more details see text. The observed data can be interpreted within existing models for dirty metals. Note that the results also approximately match the results of Fig.

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. Similarly, the FFT-peak width of one R B -trace is only one-third of the peak width expected from the geometry sample dimensions.

Horizontal lines indicate frequencies for inner, mean, and outer radii as illustrated in the inset. Series I Physics Physique Fizika. We observe that with increasing edge roughness the features of quantization and magnetic focusing weaken until they resemble a shoulder-like structure that was observed in the experiments.

A smaller radius will lead to a larger oscillation amplitude, which may explain the improved amplitude in our measurements. The observations are in good agreement with an interpretation in terms of diffusive metallic grapehne in a ring geometry. Arrows indicate the direction of the edge channels.

Magdalena Huefner et al New J.