Discovery of Superconductivity in 2M WS₂ with Possible Topological Surface States

Abstract

Recently, VIB-group layered transition metal dichalcogenides (TMDs), MX 2 (M = Mo, W; X = S, Se, Te), attracted extensive attention due to rich physiochemical properties, ranging from catalysis, [1][2][3] topological states, [4][5][6][7][8][9][10][11][12][13][14][15][16] valley polarization, [17][18][19][20][21][22] even to superconductivity. [23][24][25][26][27][28] These multiple electronic properties essentially originate from varied crystal structures of TMD materials. The typical crystal structure in TMD materials is the 2H-type structure with [X-M-X] atoms in ABA stacking in each monolayer (Figure S1a, Supporting Information). Usually, 2H MX 2 materials are semiconducting, such as, 2H MoS 2 , where the valley polarization was widely studied. [17][18][19] Also, Ising superconductivity was observed when the TMD materials are reduced down to a few or even oneRecently the metastable 1T′-type VIB-group transition metal dichalcogenides (TMDs) have attracted extensive attention due to their rich and intriguing physical properties, including superconductivity, valleytronics physics, and topological physics. Here, a new layered WS 2 dubbed "2M" WS 2 , is constructed from 1T′ WS 2 monolayers, is synthesized. Its phase is defined as 2M based on the number of layers in each unit cell and the subordinate crystallographic system. Intrinsic superconductivity is observed in 2M WS 2 with a transition temperature T c of 8.8 K, which is the highest among TMDs not subject to any fine-tuning process. Furthermore, the electronic structure of 2M WS 2 is found by Shubnikov-de Haas oscillations and first-principles calculations to have a strong anisotropy. In addition, topological surface states with a single Dirac cone, protected by topological invariant Z 2 , are predicted through first-principles calculations. These findings reveal that the new 2M WS 2 might be an interesting topological superconductor candidate from the VIB-group transition metal dichalcogenides.

Gate‐Tunable Electrical Transport in Thin 2M‐WS2 Flakes

“…It shows that the hole-type carriers are dominant in the 2M-WS 2 crystals, which is consistent with the results reported in the literature. [5] The slope of the line fits to R xy (B) increases with increased V g . The carrier concentration n can be calculated according to the formula n = 1/R h e, where R h is the Hall coefficient and e is the charge on electron.…”

“…Mater. 2019, 5,1900462 2M-WS 2 , which induces electron doping, the hole concentration decreases. As we know, the carrier concentration is a key factor for the superconductivity.…”

“…It has the highest intrinsic T c of 8.9 K among all the TMDs. [5] Its crystal structure has a symmetry of a monoclinic space group C2/m. The crystal structure of 2M-WS 2 has a different stacking order along the c-axis, compared with the known T d -WTe 2 or 1T′-MoTe 2 , where "2" indicates the number of monolayers in each unit cell and "M" represents the monoclinic lattice.…”

“…In particular, our complete phase diagram for the first time provides fresh insights into the relations between the superconducting state and various other electronic states.2M-WS 2 is a metastable phase among TMDs that was first reported in our previous paper. [5] It owns a layered structure with monoclinic space group C2/m, in which each atomic Electrolyte gating has been employed as an effective way to modulate the electronic properties of transition metal dichalcogenides (TMDs) by carrier doping over a wide range. Here, the carrier density of a new metastable phase of TMD material 2M-WS 2 is controlled by electrolyte gating to achieve reversible transitions between the superconducting state, metallic state, and insulating state.…”

Synthesis of Textured Tungsten Disulfide Nanosheets and their Catalysis for Benzylamine Coupling Reaction

“…The apparent asymmetry of the diffraction peak corresponding to the (100) in the XRD pattern might be caused by the superposition of the diffraction peaks of the oxides on the surface of the sample, which could be learned from the subsequent XPS characterization. Figure b was the schematic diagram of 2H‐WS 2 crystal structure, in which sandwich structure was composed of three atomic layers from the diagram by hexagonal closest stacking . The layered WS 2 was formed by the combination of single‐layer structure with van der Waals forces.…”