Evidences of Topological Surface States in the Nodal-Line Semimetal SnTaS₂ Nanoflakes

Abstract

Exploring the topological surface state of a topological semimetal by the transport technique has always been a big challenge because of the overwhelming contribution of the bulk state. In this work, we perform systematic angular-dependent magnetotransport measurements and electronic band calculations on SnTaS2 crystals, a layered topological nodal-line semimetal. Distinct Shubnikov–de Haas quantum oscillations were observed only in SnTaS2 nanoflakes when the thickness was below about 110 nm, and the oscillation amplitudes increased significantly with decreasing thickness. By analysis of the oscillation spectra, together with the theoretical calculation, a two-dimensional and topological nontrivial nature of the surface band is unambiguously identified, providing direct transport evidence of drumhead surface state for SnTaS2. Our comprehensive understanding of the Fermi surface topology of the centrosymmetric superconductor SnTaS2 is crucial for further research on the interplay of superconductivity and nontrivial topology.

Variations of topological surface states of nodal line semimetal AlB₂ after adsorption in aqueous environment

“…拓扑材料，包括拓扑绝缘体 (topological insulator, TI) [1] 、拓扑超导体 (topological superconductor, TSC) [2] 和拓扑半金属 (topological semimetal， TSM) [3] ，近年来引起了极大的研究热潮。拓扑材料的研究从有能隙的 TI 和 TSC 开始，然后扩展到在费米能级 (Fermi level, EF) 周围具有拓扑非平庸能带交 叉点的无能隙的 TSM。TSM 可以大致分为具有相反手性的双重简并外尔点的外尔 半金属 (Weyl semimetal, WSM) [4] 、具有四重简并狄拉克点的狄拉克半金属 (Dirac semimetal, DSM) [5] 和在第一布里渊区 (Brillouin zone, BZ) 内具有连 续节点的节线半金属 (nodal line semimetal, NLSM) [6] 。这些材料均拥有一个 奇异的特性，即体-边界对应。这代表着如果材料体相拥有非平庸的能带拓扑， 那么在边缘会出现 TSS，如 TI 表面狄拉克锥表面态 [7] ，TSC 的马约拉纳零能模 (Majorana zero mode, MZM) [8] ，WSM/DSM 表面的费米弧/费米环 [9,10] ，以及 NLSM 节线间的鼓膜状 TSS [11] 。 虽然拓扑半金属具有许多引人入胜的理论预测和独特的物理性质， 但在实际 应用方面确实存在一些挑战。近年来，人们对研究拓扑材料在能量转换、存储， 以及器件中的潜在应用越来越感兴趣， 而这也与电化学过程中的表面吸附密切相 关 [12][13][14][15] 。对拓扑材料表面反应的研究始于三维 TI 材料 Bi2Se3，通过在其表面覆盖 一层金原子，探讨对一氧化碳分子的吸附。该工作提出 Bi2Se3 材料中的 TSS 狄拉 克锥能带作为有效的"电子浴"可以调制 Au 对 CO 的吸附能，使得 Au 具有更强 的 CO 氧化催化能力 [16] 。随后，Bi2Se3 覆盖单层 ZnSe(1-ML ZnSe/Bi2Se3)被发现 在 ZnSe 表面具有良好的 HER 性能，即表面氢吸附吉布斯自由能∆𝐺 𝐻 * 接近 0 eV， 并且在吸附 H 原子后狄拉克锥结构的位置发生了变化， 说明拓扑表面态参与了催 化过程 [17] 。近几年，更多的 TI 材料被人们发现具有较好的 HER 性能，如 Bi2Te3 [18,19] 、Li2Pt [20] 等。 然而，在 TI 参与的催化过程中，由于其体相的低电导率会增加电荷转移电 阻、降低电荷-空穴分离效率，从而不利于催化动力学。TSM 因其较高的化学稳 定性和电导率而受到越来越多的关注。最早 WSM 家族(NbP、TaP、NbAs、TaAs)…”

The Coexistence of Superconductivity and Topological Order in Van der Waals InNbS2

“…[13][14][15][16][17] Since strong spin-orbit coupling (SOC) often favors nontrivial band topology and topological superconductivity, a promising direction is to explore material systems with enhanced SOC. [18][19][20] This research field is still in its nascent stage, especially the scarcity of appropriate material platforms still poses a significant challenge.…”

Planar Hall Effect in the Charge-Density-Wave Bi2Rh3Se2

“…[1] Numerous quantum materials have been discovered and extensively studied, including graphene, [2] superconductors such as AV3Sb5 (A = K, Rb, Cs), [3] UTe2, [4] topological semi-metals such as PtBi2, [5,6] ZrSiS, [7] and so on. Lately, two-dimensional ternary chalcogenides, such as PaTaSe2, [8,9] SnTaS2, [10,11] and InTaSe2, [12] have attracted a great deal of attention by their unique architecture, novel physical characteristics, and promising potential application in nanodevices. [13] Recently, the ternary chalcogenide Bi2Rh3Se2 was closely investigated for its fancy charge-density-wave and superconductivity.…”