Record-High Superconductivity in Transition Metal Dichalcogenides Emerged in Compressed 2H-TaS2

Pressure has always been an effective method for uncovering novel phenomena and properties in condensed matter physics. Here, an electrical transport study is carried on 2H-TaS₂ up to ≈208 GPa, and an unexpected superconducting state (SC-II) emerging around 86.1 GPa with an initial critical temperature (T_c ) of 9.6 K is found. As pressure increases, the T_c enhances rapidly and reaches a maximum of 16.4 K at 157.4 GPa, which sets a new record for transition metal dichalcogenides (TMDs). The original superconducting state (SC-I) is found to be re-enhanced above 100 GPa after the recession around 10 GPa, and coexists with SC-II to the highest pressure applied in this work. In situ high-pressure X-ray diffraction and Hall effect measurements reveal that the occurrence of SC-II is accompanied by a structural modification and a concurrent enhancement of hole carrier density. The new high-T_c superconducting state in 2H-TaS₂ can be attributed to the change of the electronic states near the Fermi surface, owing to pressure-induced interlayer modulation. It is the first time finding this remarkable superconducting state in TMDs, which not only brings a new broad of perspective on layered materials but also expands the field of pressure-modified superconductivity.

Imprinting Ferromagnetism and Superconductivity in Single Atomic Layers of Molecular Superlattices

Ferromagnetism and superconductivity are two antagonistic phenomena since ferromagnetic exchange fields tend to destroy singlet Cooper pairs. Reconciliation of these two competing phases has been achieved in vertically stacked heterostructures where these two orders are confined in different layers. However, controllable integration of these two phases in one atomic layer is a longstanding challenge. Here, an interlayer-space-confined chemical design (ICCD) is reported for the synthesis of dilute single-atom-doped TaS₂ molecular superlattice, whereby ferromagnetism is observed in the superconducting TaS₂ layers. The intercalation of 2H-TaS₂ crystal with bulky organic ammonium molecule expands its van der Waals gap for single-atom doping via co-intercalated cobalt ions, resulting in the formation of quasi-monolayer Co-doped TaS₂ superlattices. Isolated Co atoms are decorated in the basal plane of the TaS₂ via substituting the Ta atom or anchoring at a hollow site, wherein the orbital-selected p-d hybridization between Co and neighboring Ta and S atoms induces local magnetic moments with strong ferromagnetic coupling. This ICCD approach can be applied to various metal ions, enabling the synthesis of a series of crystal-size TaS₂ molecular superlattices.