We proposed that BaHgSn is a Dirac semimetal (DSM) which can host hourglasslike surface states (HSSs) as protected by nonsymmorphic glide symmetry. Compared to KHgSb, an isostructural topological crystalline insulator with the same HSSs, BaHgSn has an additional band inversion at the $\mathrm{\Gamma }$ point. This band inversion is induced by the stronger interlayer coupling among Hg-Sn honeycomb layers than that among Hg-Sb layers in KHgSb, which leads to bulk Dirac nodes in BaHgSn along the layer stacking direction $\mathrm{\Gamma }-A$. In addition, the mirror Chern number $C_i$ protected by the mirror plane ${\overline{M}}_z$ ($k_z=0$) changes from 2 in KHgSb to 3 in BaHgSn. Therefore, when a compressive uniaxial strain is applied along the $y$ axis to break the rotation symmetry protecting the DSM state, BaHgSn becomes a strong topological insulator with $Z_2$ indices of $(1;000)$ and the topological surface Dirac cone coexists with HSSs on the (010) surface. The Wilson-loop spectra have been calculated to verify these topological features. The calculated surface states, the Fermi surfaces and their quasiparticle interference patterns are ready to be compared with experimental measurements.

中文翻译：

---

BaHgSn：带有表面沙漏费米子的狄拉克半金属

我们提出，BaHgSn是一种狄拉克半金属（DSM），可以承载沙漏状的表面态（HSSs），并受到非对称滑移对称性的保护。与具有相同HSS的同构拓扑晶体绝缘体KHgSb相比，BaHgSn在KHS处具有额外的能带反转。$\mathrm{\Gamma }$点。该带反转是由Hg-Sn蜂窝层之间的层间耦合比KHgSb中的Hg-Sb层之间的层间耦合更强引起的，从而导致BaHgSn中沿层堆叠方向的体Dirac节点$\mathrm{\Gamma }-\mathrm{一种}$。另外，镜子陈恩数$C_{\mathrm{一世}}$ 受镜面保护 ${\overline{\mathrm{中号}}}_{ž}$ （${ķ}_{ž}=0$）从KHgSb中的2变为BaHgSn中的3。因此，当沿轴向施加压缩单轴应变时$ÿ$ 轴破坏了保护DSM状态的旋转对称性，BaHgSn成为具有以下特征的强拓扑绝缘体 ${ž}_2$ 的指数 $（\mathrm{1个};000）$拓扑表面Dirac锥与（010）表面的HSS共存。已计算出威尔逊环谱以验证这些拓扑特征。可以将计算出的表面状态，费米表面及其准粒子干涉图样与实验测量结果进行比较。