Graphene p–n and p–n–p Junction Devices

Here is another article I would like to read if I had the $32.00.

Nature | Letter

Designer Dirac fermions and topological phases in molecular graphene

• Kenjiro K. Gomes,^{1, 2, 6}
• Warren Mar,^{2, 3, 6}
• Wonhee Ko,^{2, 4, 6}
• Francisco Guinea⁵
• & Hari C. Manoharan^{1, 2}

• Affiliations
• Contributions
• Corresponding author

Journal name:

Nature

Volume:

483,

Pages:

306–310

Date published:

(15 March 2012)

DOI:

doi:10.1038/nature10941

Received

08 July 2011

Accepted

09 February 2012

Published online

14 March 2012           

The observation of massless Dirac fermions in monolayer graphene has generated a new area of science and technology seeking to harness charge carriers that behave relativistically within solid-state materials¹. Both massless and massive Dirac fermions have been studied and proposed in a growing class of Dirac materials that includes bilayer graphene, surface states of topological insulators and iron-based high-temperature superconductors. Because the accessibility of this physics is predicated on the synthesis of new materials, the quest for Dirac quasi-particles has expanded to artificial systems such as lattices comprising ultracold atoms^{2, 3, 4}. Here we report the emergence of Dirac fermions in a fully tunable condensed-matter system—molecular graphene—assembled by atomic manipulation of carbon monoxide molecules over a conventional two-dimensional electron system at a copper surface⁵. Using low-temperature scanning tunnelling microscopy and spectroscopy, we embed the symmetries underlying the two-dimensional Dirac equation into electron lattices, and then visualize and shape the resulting ground states. These experiments show the existence within the system of linearly dispersing, massless quasi-particles accompanied by a density of states characteristic of graphene. We then tune the quantum tunnelling between lattice sites locally to adjust the phase accrual of propagating electrons. Spatial texturing of lattice distortions produces atomically sharp p–n and p–n–p junction devices with two-dimensional control of Dirac fermion density and the power to endow Dirac particles with mass^{6, 7, 8}. Moreover, we apply scalar and vector potentials locally and globally to engender topologically distinct ground states and, ultimately, embedded gauge fields^{9, 10, 11, 12}, wherein Dirac electrons react to ‘pseudo’ electric and magnetic fields present in their reference frame but absent from the laboratory frame. We demonstrate that Landau levels created by these gauge fields can be taken to the relativistic magnetic quantum limit, which has so far been inaccessible in natural graphene. Molecular graphene provides a versatile means of synthesizing exotic topological electronic phases in condensed matter using tailored nanostructures.