Diamond-like incompressibility coexisting with superconductivity in a cluster Mott system

We studied the structural and electronic evolution of the lacunar spinel GaNb₄Se₈ under high pressure using a combination of synchrotron X-ray diffraction, Raman spectroscopy, and electrical transport measurements in diamond-anvil cells. At ambient pressure, GaNb₄Se₈ is a narrow-gap Mott insulator composed of well-defined Nb₄ tetrahedral clusters separated by GaSe₄ units. Upon compression, the diffraction data reveal a continuous lattice contraction followed by a structural phase transition near 20 GPa, from a cubic to a monoclinic phase.

Electrical transport measurements indicate a strong pressure-induced metallization. The resistivity decreases by several orders of magnitude, and a clear superconducting transition emerges above ~30 GPa with a critical temperature around 5 K. The results demonstrate that external pressure can effectively tune the balance between electronic correlation and bandwidth in this cluster-based compound.

Our observations provide direct evidence that superconductivity can develop in a lattice previously considered mechanically rigid and electronically localized. This work contributes to a broader understanding of how pressure can drive Mott insulators into superconducting states and may help guide future exploration of correlated and cluster-based quantum materials.