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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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Ferrari A C et al Phys. In diffusive ring-shaped systems, conductance fluctuations can coexist with Aharonov—Bohm oscillations. Received 24 November Published 30 April This indicates that thermal averaging of interference contributions to the conductance is expected to be relevant.

It supports the sharing of ideas and thoughts within the vohm community, fosters physics teaching and would also like to open a window to physics for all those grapehne a healthy curiosity. 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. Sign up for new issue notifications. Moreover we show signatures of magnetic focusing effects at small magnetic fields confirming ballistic transport.

B 80 Crossref. The DPG sees itself as the forum and mouthpiece for physics and is a non-profit organisation that does not pursue financial interests. However, due to limited sample stability, the visibility of the oscillations at a given back gate voltage depends on the back gate voltage history.

A magnetic field is applied perpendicular to the aharojov plane. B 77 Crossref. The lower panel shows the semiclassically calculated transmission through the ring for more details see text. Minima and maxima of the conductance are approximately horizontal and vertical grahene this plot.

Curves are plotted with offsets for clarity. B 79 Crossref. We also note that the diffusive regime investigated in our device is quite extended in back gate voltage.

The inset highlights cycloid drift motion of an edge channel along the charge puddle. While the earlier research interests were focused on the most basic nanostructures, e. Solid lines highlight constant cyclotron radii for selected values. Electron beam lithography followed by reactive ion etching is used to define the structure.


This interference can be tuned via the AB phase of the area green and red encircled. The red trace in the inset corresponds to the mirrored and vertically offset negative B -field branch.

Figure 4 a Schematic representation of the different ring geometries of samples 1 and 2. Zoom In Zoom Out Reset image size.

[] The Aharonov-Bohm effect in graphene rings

Therefore measurements presented here were taken over only small ranges of back gate voltage after having allowed the sample to stabilize in this range. Finally, we report on the observation of the AB conductance oscillations in the quantum Hall regime at reasonable high magnetic fields, where we find regions with enhanced AB oscillation visibility with values up to 0.

Figure 1 a Scanning force microscopy image of device 1 with a schematic of the measurement configuration. By continuing to use this site you agree to our use of cookies.

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Series I Physics Physique Fizika. The density change is related via a parallel plate capacitor model to a change in back gate voltage, i. The amplitude of the Aharonov—Bohm oscillations is modulated aharonof a 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.

The observed data can be interpreted within existing models for dirty metals. Arrows indicate the direction of the edge channels.

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

B 75 Crossref. 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. Sign up to receive regular email alerts from Physical Review B. The data are analyzed by a simple dirty metal model justified by a comparison of the different length scales characterizing the system.


B 40 Crossref. On the other hand, the electric field may change the electron density and thereby the Fermi wavelength of the carriers.

A close up of the 4. It was speculated that this small value might be due to inhomogeneities in the two interferometer arms, leading to a tunneling constriction that suppressed the oscillations. 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. The main advantage of graphene compared to metals for Aharonov—Bohm studies is the reduced screening.

We observe that the trajectory of the electron starting in the left lead performs a skipping hohm which after four reflections bohj the boundary enters the right lead. We have observed Aharonov—Bohm oscillations in four-terminal measurements on a side-gated graphene ring structure. 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 observations are in good agreement with an interpretation in terms of diffusive metallic transport in a ring geometry. We identify the relevant transport regime in terms of appropriate length scales. In order to determine this lever arm ratio, we have performed measurements of conductance fluctuations in traphene plane of the back gate voltage V BG and the side gate voltage V SG not shown. We ahafonov speculate ahaonov 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.

Standard low-frequency lock-in techniques are used to graphdne the resistance by applying a constant current. Note that in order for interference to happen at all, part of the wave function has to leak to the reflecting edge channel as otherwise unitarity ensures perfect transmission.

The measured resistance R meas consists of the following parts: