Dirac materials in square lattice compounds

表现出与石墨烯相同的电子结构但是三维的材料(即所谓的3D狄拉克半金属)最近受到了基础科学和应用科学的极大关注。这一次，它们表现出了特殊的物理性质，如非常高的磁阻或载流子迁移率，但它们也可以导致发现高能物理中预测的新粒子，但如果材料具有正确的能带结构，就可以在固态下观察到这些新粒子。目前，这类3D狄拉克半金属材料的数量有限，其中许多材料要么在基本性质上存在缺陷，即它们的电子结构，要么由于它们的毒性、成本或在环境条件下的不稳定性，它们在未来的设备中使用的潜力也存在缺陷。这项提议的目的是找到更多不存在这些缺点的3D狄拉克材料。最近，我们介绍了一种新材料，ZrSiS，它不仅是目前3D Dirac材料的一种廉价、稳定和无毒的替代品，而且还具有基础物理感兴趣的电子结构。一方面，狄拉克能带在很大的能量范围内线性分散，这使得晶体中有更多的缺陷，同时费米能级仍然位于线性分散的能带区域内。另一方面，ZrSiS具有一个受非对称对称性保护的狄拉克锥体，这是一种跨国对称元素，在预测新的狄拉克材料和新的费米子方面引起了理论界的极大兴趣。我们首次证明了在实验上观察到电子结构中的这一预测特征是可能的。现在，我们想要扩大具有相关电子结构的材料的数量。为了寻找更多具有这种有趣的物理性质的材料，ZrSiS是一个很好的起点。这一次，它在共同的晶体结构(PbFCl结构类型)中结晶，但电子结构的重要特征可以追溯到原子的方形网状排列，这一特征也可以出现在更多的结构类型中，从而允许非常大量的化合物进行探索。我们将通过从头计算识别感兴趣的材料，合成它们，并用角度分辨光电子能谱(ARPES)和输运研究来研究它们。

Materials that exhibit the same electronic structure as graphene but are three dimensional (so called 3D Dirac Semimetals) have received a lot of attention recently from both fundamental and applied sciences. For once they exhibit exceptional physical properties such as very high magnetoresistance or carrier mobility, but they can also lead to the discovery of new particles that were predicted in high energy physics, but can be observed in the solid state if the materials has the correct band structure. Currently the amount of such 3D Dirac semimetals is limited and many of them show either drawbacks in their fundamental properties, i.e. their electronic structure or also in their potential to be used in future devices due to their toxicity, cost or instability in ambient conditions. The aim of this proposal is to find more 3D Dirac materials that do not bear these disadvantages. Recently we introduced a new material, ZrSiS, that is not only a cheap stable and non toxic alternative to current 3D Dirac materials, but also has an electronic structure that is of interest for fundamental physics. On the one hand the Dirac bands are linearly dispersed over a very large range of energy which allows for more defects in the crystals while still having the Fermi level located within the region of linearly dispersed bands. On the other hand ZrSiS features a Dirac cone that is protected by non-symmorphic symmetry, a transnational symmetry element that has gained significant interest by theorists for the prediction of new Dirac materials and also new fermions. We showed for the first time that it is possible to observe this predicted feature in the electronic structure experimentally. Now, we would like to expand the number of materials with related electronic structures. ZrSiS is a good starting point to look for more materials with this interesting physical properties. For once, it crystallizes in a common crystal structure (PbFCl structure type), but also, the important feature for the electronic structure can be traced back to the square net arrangement of atoms, a feature that can also arise in many more structure types, allowing for a very large number of compounds to explore. We will identify materials of interest with ab initio calculations, synthesize them, and investigate them with angle resolved photoemission spectroscopy (ARPES) and transport studies.