Abstract
Non-symmorphic materials have recently been predicted to exhibit many different exotic features in their electronic structures. These originate from forced band degeneracies caused by the non-symmorphic symmetry, which not only creates the possibility to realize Dirac semimetals, but also recently resulted in the prediction of novel quasiparticles beyond the usual Dirac, Weyl or Majorana fermions, which can only exist in the solid state. Experimental realization of non-symmorphic materials that have the Fermi level located at the degenerate point is difficult, however, due to the requirement of an odd band filling. In order to investigate the effect of forced band degeneracies on the transport behavior, a material that has such a degeneracy at or close to the Fermi level is desired. Here, we show with angular resolved photoemission experiments supported by density functional calculations, that ZrSiTe hosts several fourfold degenerate Dirac crossings at the X point, resulting from non-symmorphic symmetry. These crossings form a Dirac line node along XR, which is located almost directly at the Fermi level and shows almost no dispersion in energy. ZrSiTe is thus the first real material that allows for transport measurements investigating Dirac fermions that originate from non-symmorphic symmetry.
Highlights
Non-symmorphic space groups force band degeneracies at high symmetry points in the Brillouin Zone (BZ), which makes materials in these space groups ideal candidates for Dirac semimetals (DSMs) in two or three dimensions [1, 2]
We show with angular resolved photoemission (ARPES) experiments and density functional theory (DFT) calculations that ZrSiTe exhibits a Dirac crossing protected by non-symmorphic symmetry very close to the Fermi level that is stabilized by other pockets located at other parts in the BZ, allowing the non-symmorphic degeneracy to be at the Fermi level in a closed-shell system
The layered structure of ZrSiTe and the cleavage plane, which is located between the two Zr-Te layers, was imaged with High-resolution transmission electron microscopy (HRTEM) in the [100]-direction, as shown in Fig. 1c
Summary
Non-symmorphic space groups force band degeneracies at high symmetry points in the Brillouin Zone (BZ), which makes materials in these space groups ideal candidates for Dirac semimetals (DSMs) in two or three dimensions [1, 2]. To have a “clean” non-symmorphic DSM, an isolated half-filled band is required [5] This can be understood if one considers that the translational part of the non-symmorphic symmetry causes a folding of the BZ, which results in the forced band degeneracies. Examples are the alkali metals or coppermonochalcogenides (e.g. CuS) [13] For these reasons, there is currently no example of a real material that has a non-symmorphic Dirac crossing located at the Fermi level. In order to study the effect of band degeneracies forced by non-symmorphic symmetry on the transport behavior, it is crucial to find a material where such a band crossing is located at the Fermi level. We present an alternative route to achieve a material with a non-symmorphic band crossing at the Fermi level, opening the possibility to study the transport behavior of these exotic Dirac fermions
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