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Abstract
After the discovery of Dirac fermions in graphene, it has become a natural question to ask whether it is possible to realize Dirac fermions in other two-dimensional (2D) materials as well. In this work, we report the discovery of multiple Dirac-like electronic bands in ultrathin Ge films grown on Au(1 1 1) by angle-resolved photoelectron spectroscopy. By tuning the thickness of the films, we are able to observe the evolution of their electronic structure when passing through the monolayer limit. Our discovery may signify the synthesis of germanene, a 2D honeycomb structure made of Ge, which is a promising platform for exploring exotic topological phenomena and enabling potential applications.
Highlights
Since the discovery of the extraordinary physical and electronic properties of graphene, there has been an intense effort to synthesize two-dimensional (2D) honeycomb structures based on heavier elements than carbon in order to realize new topological phenomena that are driven by spin–orbit coupling (SOC), such as the quantum spin Hall (QSH) [1,2,3] or quantum anomalous Hall (QAH) [4, 5] effects
By performing comprehensive angle-resolved photoelectron spectroscopy (ARPES) measurements, we study the electronic structure of ultra-thin Ge films grown on Au(1 1 1)
We simulated the effect of rotational disorder on a circular Dirac cone, which can be found in the supplementary material, and nicely reproduces the parallel bands shown in figure 4(d).A momentum-distribution curve (MDC) analysis of the Dirac-like bands close to the point of the Au(1 1 1) surface Brillouin zone (BZ) in the 2.6 Å thick Ge film, shown in figure 4(e), reveals that the extrapolated apex of the cone is located at 90 meV binding energy
Summary
Since the discovery of the extraordinary physical and electronic properties of graphene, there has been an intense effort to synthesize two-dimensional (2D) honeycomb structures based on heavier elements than carbon in order to realize new topological phenomena that are driven by spin–orbit coupling (SOC), such as the quantum spin Hall (QSH) [1,2,3] or quantum anomalous Hall (QAH) [4, 5] effects. One promising family of materials to host these exotic effects—silicene [6], germanene [6, 7], and stanene [7, 8]—is built out of the group IV elements Si, Ge and Sn, which are predicted to form buckled honeycomb structures. Similar to graphene, these structures are expected to host Dirac fermions with a linear dispersion relation in the vicinity of the K/K′ points of their hexagonal Brillouin zones. Initial reports claimed the existence of Dirac dispersions for silicene on Ag(1 1 1) [11], more recent studies found that these are likely to be caused by substrate interactions [16,17,18,19,20]
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