Pressure-induced evolution of superconductivity and structural stability in a bulk 4Hb -TaSeS heterostructure

Transition-metal dichalcogenides (TMDs) are characterized by their unique layered structures and diverse electronic properties. Recent studies have highlighted the distinctive superconducting and charge density wave (CDW) behaviors of $4{H}_{b}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ and $4{H}_{b}\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$. To explore the intriguing characteristics of these structurally modulated compounds, we synthesized $4{H}_{b}\text{\ensuremath{-}}\mathrm{TaSeS}$, which alternates between $1H$ and $1T$ layers, and investigated its structural and superconducting properties. At ambient pressure, $4{H}_{b}\text{\ensuremath{-}}\mathrm{TaSeS}$ displays superconductivity with a transition temperature (${T}_{\text{c}}$) of approximately 3.8 K. Under increasing pressure, ${T}_{\text{c}}$ decreases to a minimum of around 2.3 K at 37 GPa, followed by a gradual recovery that forms an unusual valley in the ${T}_{\text{c}}$-pressure curve. High-pressure synchrotron x-ray diffraction measurements show that $4{H}_{b}\text{\ensuremath{-}}\mathrm{TaSeS}$ maintains its hexagonal symmetry up to 82 GPa without undergoing any structural transitions. Resistivity measurements also indicate a transition from non-Fermi liquid to Fermi liquid behavior induced by pressure. Further theoretical calculations shed light on the pressure-dependent superconducting mechanism, demonstrating that superconductivity is primarily influenced by Ta atoms, with contributions predominantly from $H$-layer Ta at lower pressures, gradually shifting to $T$-layer Ta as pressure increases. These findings offer valuable insights into pressure-induced superconductivity in TMDs and other complex layered systems.