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Research confirms parity effect in graphene

11 Aug 2015  | Kensuke Kobayashi, Sadashige Matsuo, Teruo Ono

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A collaborative research of a group led by Professor Teruo Ono (Kyoto University) and Kazuhito Tsukagoshi (Lead Researcher, National Institute for Materials Science), Professor Kensuke Kobayashi (Osaka University) and Assistant Professor Sadashige Matsuo (The University of Tokyo) have theoretically projected and proven the parity effect of the quantum Hall edge transport in graphene antidot devices with pn junctions (PNJs) through experimentation.

Graphene, or single-layered graphite, has properties of both metals and semiconductors.

The group confirmed that the parity effect in graphene antidot devices has a good analogy to optical systems. This means various quantum interference devices can be produced by using the quantum Hall edge transport with pn junctions.

Parity effect

Figure 1: (a) and (b): Schematic picture of the chirality of the quantum Hall edge states around a single antidot when the number of PNJs (N) is (a) even and (b) odd. The study establishes that the conductance is essentially different between the two cases, namely the parity effect. (c) Optical image of the device. Inset shows that this device has a single open window (an antidot) shown by the white curves. Researchers tuned the top gate voltages of the top gate electrodes, marked a and b, in order to experimentally realise the cases with N = 0, 1, 2 and 3.

The group discovered the parity effect of the quantum Hall edge transport in graphene, which is a new ubiquitous phenomenon in quantum Hall edge transport in massless Dirac electron systems. The group theoretically studied a graphene device with an antidot and multiple pn junctions (PNJs) and had obtained new compact formulae to show a significant parity effect regarding the number of PNJs. They realised that such graphene devices confirm the new formulae.

The findings of the research are, as the group claims, the first to establish the parity effect on bipolar quantum Hall edge transport in massless Dirac electron systems. This is an important discovery in designing new electron interferometer devices using graphene.

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