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 & SIM;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.