Anisotropic gapping of topological Weyl rings in the charge-density-wave superconductor InxTaSe2

Commensurate Stacking Phase Transitions in an Intercalated Transition Metal Dichalcogenide

Intercalation and stacking-order modulation are two active ways in manipulating the interlayer interaction of transition metal dichalcogenides (TMDCs), which lead to a variety of emergent phases and allow for engineering material properties. Herein, the growth of Pb-intercalated TMDCs-Pb(Ta_1+x Se₂ )₂ , the first 124-phase, is reported. Pb(Ta_1+x Se₂ )₂ exhibits a unique two-step first-order structural phase transition at around 230 K. The transitions are solely associated with the stacking degree of freedom, evolving from a high-temperature (high-T) phase with ABC stacking and R3m symmetry to an intermediate phase with AB stacking and P3m1, and finally to a low-temperature (low-T) phase again with R3msymmetry, but with ACB stacking. Each step involves a rigid slide of building blocks by a vector [1/3, 2/3, 0]. Intriguingly, gigantic lattice contractions occur at the transitions on warming. At low-T, bulk superconductivity with T_c  ≈ 1.8 K is observed. The underlying physics of the structural phase transitions are discussed from first-principle calculations. The symmetry analysis reveals topological nodal lines in the band structure. The results demonstrate the possibility of realizing higher-order metal-intercalated phases of TMDCs and advance the knowledge of polymorphic transitions, and may inspire stacking-order engineering in TMDCs and beyond.

Superconductivity in quasi-2D InTaX2(X = S, Se) type-II Weyl semimetals

Herein, first-principles calculations were employed to study the electronic, topological, and superconducting properties of InTaX₂(X = S, Se). InTaX₂exhibits nodal lines in the absence of spin-orbit coupling (SOC); on SOC inclusion, the nodal lines form Weyl rings with the Weyl points classified as a type-II Weyl semimetal (WSM) with tilted cones. Using Green functions method calculations, surface states distinguishable from the bulk states, and Fermi arcs surface states were visualized on the (001) easily cleavable indium terminated surface of both materials. The electron-phonon calculations using the Allen-Dynes relations predict InTaSe₂and InTaS₂to be superconducting around 2.38 K and 3.25 K. The prediction of these exotic properties in InTaX₂(X = S, Se) makes them suitable for experimental validation of topological superconductivity in type-II WSMs.