In addition, the linear dispersion relation of low-energy excitations at the Weyl nodes and the distinct (opposite) chiralities of WFM have pronounced consequences on magnetotransport phenomena in WSM. (8,12) WSM properties can occur in the material fulfilling the abovementioned symmetry conditions if two bands without spin degeneracies cross in the close vicinity in the Brillouin zone the crossing points are named Weyl nodes. (8) In DSM, both time-reversal and inversion symmetry must be obeyed, whereas in WSM, one of those has to be broken. WSM can be derived from slightly earlier known Dirac semimetals (DSM) by lowering necessary symmetry conditions fulfilled by the respective material. (1,2) The possibility of condensed matter realization of formerly elusive Weyl fermions emerging as a zero mass solution of the Dirac equation derived by Weyl already in 1929, (3) recently generated a lot of interest in both theoretical (4−7) and experimental (1,2,8−11) solid-state physics. TaAs is the first experimentally recognized Weyl semimetal (WSM). Both X-ray diffraction and transmission electron microscopy measurements indicate that the columns share the same orientation and crystalline structure. Atomic force microscopy imaging reveals the columnar structure of the layers, with lateral (parallel to the layer’s surface) columns about 20 nm wide and 200 nm long. Thorough X-ray diffraction measurements and analysis of the in situ reflection high-energy electron diffraction images indicate that TaAs layers are fully relaxed already at the initial deposition stage. Only stacking fault defects in TaAs are detected by transmission electron microscopy. In spite of a substantial lattice mismatch (about 19%) between the GaAs(001) substrate and TaAs epilayer, no misfit dislocations are observed at the GaAs(001)/TaAs(001) interface. The (001) planes of the tetragonal TaAs lattice are parallel to the GaAs(001) substrate, but the corresponding in-plane crystallographic directions of the substrate and the layer are rotated by 45°. Thin crystalline layers of TaAs Weyl semimetal are grown by molecular beam epitaxy on GaAs(001) substrates.
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