Condensed matter systems provide a rich setting to realize Dirac and Majorana
excitations and the possibility to manipulate them in materials for potential applications.
Recently, it has been proposed that Weyl
fermions, which are chiral, massless particles, can emerge in certain bulk
materials or in topological insulator multilayers and can produce unusual
transport properties, such as charge pumping driven by a chiral anomaly. A pair
fermions protected by crystalline symmetry, effectively forming a massless
Dirac fermion, has been predicted to appear as low energy excitations in a
number of candidate materials termed three-dimensional (3D) Dirac semimetals.
This paper reports the first scanning tunneling microscopy (STM) on one
promising host material, the II-V semiconductor Cd3As2.
The study provides the first atomic scale probe of Cd3As2,
showing that defects mostly influence the valence band, consistent with the
observation of ultra-high mobility carriers in the conduction band. By
combining Landau level spectroscopy and quasiparticle
interference (QPI) at ultra low temperatures and high magnetic fields, they
distinguish a large spin-splitting of the conduction band in a magnetic field
its extended Dirac-like dispersion above the expected regime. A model band
structure consistent with the experimental findings suggests that for a
specific orientation of the applied magnetic field, Weyl
fermions are the low-energy excitations in Cd3As2.
Jeon, Brian B. Zhou, Andras Gyenis, Benjamin E. Feldman,
Itamar Kimchi, Andrew C. Potter, Quinn D. Gibson, Robert J. Cava, Ashvin
Vishwanath and Ali Yazdani
Nature Materials (2014), in press.
Landau level spectra of the local tunneling density of states at high magnetic fields and low temperatures
of Cd3As2 . (Left) Analysis of such data can be
used to map the Dirac band structure of this material over a wide range energy
both below and above the chemical potential