Origin of the decompression driven superconductivity enhancement in SnSe₂

Tin diselenide (SnSe₂) is a typical layered material of the main-group metaldichalcogenides, and exhibits superconductivity under pressure. In this work, the enhanced superconductivity of SnSe₂ is reported in decompression and the key mechanism behind the decompression driven superconductivity enhancement is revealed. We explore SnSe₂, transforming into superconductivity at ∼22 GPa, above which the superconductivity is robust up to 42.8 GPa. Interestingly, when the pressure gradually decreases to 14.0 GPa, the T_c increases monotonously from 6.0 K to 7.9 K. The observed unusual evolution of superconductivity was explained by a combination of pressure-manipulated carrier concentration and phonon softening during decompression by both experimental and theoretical studies. First-principles calculations reveal that interlayer Se-Se bonding is responsible for the series of changes. Our results demonstrate that interlayer coupling is critical for the superconductive behavior of the layered main-group metal dichalcogenides and provides a new platform to study the compressed superconductivity of layered compounds at low pressures.