Main navigation | Main content

« *fall 2014* - spring 2015 - summer 2015 »

This week | Next week | This semester | All future | Print view

This week | Next week | This semester | All future | Print view

Wednesday, November 12th 2014

3:35 pm:

The observation of massless Dirac fermions in monolayer graphene has propelled a new area of science and technology seeking to harness charge carriers that behave relativistically within solid-state materials. Using low-temperature scanning tunneling microscopy and spectroscopy, we show the emergence of Dirac fermions in a fully tunable condensed-matter system—molecular graphene—assembled via atomic manipulation of a conventional two-dimensional electron system in a surface state. We embed, image, and tune the symmetries underlying the two-dimensional Dirac equation into these electrons by sculpting the surface potential with manipulated molecules. By distorting the effective electron hopping parameters into a Kekulé pattern, we find that these natively massless Dirac particles can be endowed with a tunable mass engendered by the associated scalar gauge field, in analogy to the Higgs field. With altered symmetry and texturing of the assembled lattices, the Dirac fermions can be dressed with gauge electric or magnetic fields such that the carriers believe they are in real fields and condense into the corresponding ground state, as confirmed by tunneling spectroscopy. Using these techniques we ultimately fabricate a quantum Hall state without breaking time-reversal symmetry, in which electrons quantize in a gauge magnetic field ramped to 60 Tesla with zero applied laboratory field. We show that these and other chiral states now possible to realize have direct analogues in topological insulators, and can be used to guide or confine charge in nontrivial ways [1,2].

[1] K. K. Gomes, W. Mar, W. Ko, F. Guinea, H. C. Manoharan, “Designer Dirac Fermions and Topological Phases in Molecular Graphene,” Nature 483, 306–310 (2012).

[2] M. Polini, F. Guinea, M. Lewenstein, H. C. Manoharan, V. Pellegrini, “Artificial Honeycomb Lattices for Electrons, Atoms, and Photons,” Nature Nanotechnology 8, 625–633 (2013).

The weekly calendar is also available via subscription to the physics-announce mailing list, and by RSS feed.