The metallic character of the GeBi 2 Te 4 single crystals is probed using a combination of structural and physical properties measurements, together with density functional theory (DFT) calculations. The structural study shows distorted Ge coordination polyhedra, mainly of the Ge octahedra. This has a major impact on the band structure, resulting in bulk metallic behavior of GeBi 2 Te 4 , as indicated by DFT calculations. Such calculations place GeBi 2 Te 4 in a class of a few known nontrivial topological metals, and explains why an observed Dirac point lies below the Fermi energy at about −0.12 eV. A topological picture of GeBi 2 Te 4 is confirmed by the observation of surface state modulations by scanning tunneling microscopy.

We have studied nonlocal electrical transport over macroscopic distances in the regime of the fractional quantum Hall effect (FQHE). Experiments clearly demonstrate dissipationless edge state conduction associated with the FQHE. Surprisingly, our data imply that there is no edge state conduction near ν=1/2 and on the low ν side of the ν=1 QHE state, while there is edge state conduction near ν=3/2 and on the high ν side of the ν=1 QHE state. We also observe that the electron-hole symmetry is broken for the edge states in a confined geometry. We develop a picture of edge state structure consistent with these observations.