Nov 26, 2020 
Taking correlated quantum Hall physics to the third dimension
(Nanowerk News) The quantum Hall effect is among the most prominent examples of a quantum phenomenon that occurs on a truly macroscopic scale. Its robust nature renders the quantum Hall effect vastly important for applications. It is nowadays for example used as the “gold standard” to gauge electric resistances.

Even more importantly, the quantum Hall effect can be considered a drosophila for topological physics, and numerous topological states of matter can be understood building on the fundamental insights gained in connection to the quantum Hall effects over the past decades.

Traditionally, the quantum Hall effect has exclusive been associated with twodimensional metals. Now, scientists at the Max Planck Institute for Chemical Physics of Solids in Dresden, the Technische Universität Dresden, the Brookhaven National Laboratory at New York, the HelmholtzZentrum DresdenRossendorf, the University of the Chinese Academy of Sciences, and the WuerzburgDresden Cluster of Excellence ct.qmat have discovered a new strongly correlated electronic state in a threedimensional metal that is a close relative of the twodimensional quantum Hall state (Nature Communications, "Unconventional Hall response in the quantum limit of HfTe5").


Hall resistivity as a function of magnetic field at 2 K in units of the Planck constant h, the elementary charge e and the Fermi wavevector along the magnetic field kF,z. (Image: MPI CPfS )

The team found signatures of an unconventional Hall response in the quantum limit of the bulk metal HfTe5, adjacent to the threedimensional quantum Hall effect of a single electron band at low magnetic fields.

The additional plateaulike feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikovde Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the threedimensional quantum Hall effect.

The findings are consistent with strong electronelectron interactions stabilizing an unconventional variant of the Hall effect in a threedimensional material in the quantum limit.

Given that topological states of matter have been of utmost importance in our understanding of twodimensional systems, these new findings promise exciting future insights.

Examining the novel properties of quantum Hall physics in threedimensional metals could not only allow scientists to better understand how far the mysterious realm of quantum Hall physics spreads, but also drive research on strongly correlated topological states in threedimensional materials in general.
