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 data are analyzed by a simple dirty metal model justified by a comparison of the different length scales characterizing the system. Figure 4 a Schematic representation of the different ring geometries of samples 1 and 2. It therefore remains unclear to us how the concept of the Thouless energy as an energy scale for wave function correlations can be transferred to the graphene system.

A smaller radius will lead to a larger oscillation amplitude, which may explain the improved amplitude in our measurements. The lower panel shows the semiclassically calculated transmission through the ring for more details see text.

For clarity the trace is duplicated with an offset see red arrow. Red dashed lines shows G 2 W used for background subtraction. 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.

The B -field axis is divided into three regimes: However, due to limited sample stability, the visibility of the oscillations at a given back gate voltage depends on the back gate voltage history. The observations are in good agreement with an interpretation in terms of diffusive metallic transport in a ring geometry.

B 76 Crossref. 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.

The observed data can be interpreted within existing models for dirty metals. Figure 1 a Scanning force microscopy image of device 1 with a schematic of the measurement configuration. Click here to close this overlay, or press the “Escape” key on your keyboard. We investigate phase-coherent transport and show Aharonov-Bohm AB oscillations in quasiballistic graphene rings with hard confinement.


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Condensed Matter > Mesoscale and Nanoscale Physics

We have observed Aharonov—Bohm oscillations in four-terminal measurements on a side-gated graphend ring structure. However, trying to relate the visibilities observed in the two experiments grapnene 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.

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 observed data can be interpreted within existing models for ‘dirty metals’. Also, our measurement temperature is about a factor of 4 higher than the lowest temperatures reported there. The exponential term aharonvo the right-hand side contains the radius of the ring r 0. The Institute of Physics IOP xharonov a leading scientific society promoting physics and bringing physicists together for the benefit of all.

The Deutsche Physikalische Gesellschaft DPG with a tradition extending back to is the largest physical society in the world with more than 61, members. Electron beam lithography followed by reactive ion etching is used to define the structure. These oscillations are well explained by taking disorder into account allowing for a coexistence of hard- and soft-wall confinement.

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Arrows indicate the direction of the edge channels. 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.

This interference can be tuned via the AB gfaphene of the area green and red encircled.

A magnetic field is applied perpendicular to the sample plane. In diffusive ring-shaped systems, conductance fluctuations can coexist with Aharonov—Bohm oscillations. 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. Finally, we report on the observation of the AB aharono 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.


It has a worldwide membership of around 50 comprising physicists from all sectors, as well as those with an interest in physics. Its publishing company, IOP Publishing, is a world leader in professional scientific communications. 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 inset highlights cycloid drift motion of an edge channel along the charge puddle.

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

In this work, we have studied the Aharonov—Bohm effect in graphene in a two-terminal ring, but using a four-contact boh. Vertical dashed lines again represent cyclotron radii as depicted in panel d. Curves are plotted with offsets for clarity. Clear periodic oscillations can be seen on top of this background. Therefore measurements presented here were taken over only small ranges of back gate voltage after having aharonpv the sample to stabilize in this range.

For b the background resistance has been subtracted as described in the text. In a semiclassical Drude picture, these resistances can be calculated from the geometric aspect ratios i.

In general, the observed Aharonov—Bohm oscillations become more pronounced for smaller current levels, as expected. We have shown that by changing the voltage applied to one of the side gates, we can induce a phase jump in the oscillations by changing the phase accumulated along this path.

This indicates that thermal averaging of interference contributions to the conductance is expected to be relevant. In athe raw data are shown, while for bthe background has been removed. Aharonob range of individual AB oscillation modes marked by arrows.

The Fermi wavelength corresponding to the carrier density mentioned above is. Series I Physics Physique Fizika. Bachtold A et al Nature Crossref. B 79 Crossref. The inset shows a close-up of the FFT spectrum.