The metal-semiconductor transition in compressed 2M-WSe₂

The application of high pressure on layered transition metal dichalcogenides (TMDs) has always been an effective way to induce exotic physical properties and novel phenomena. Here, we performed a high-pressure investigation on a newly structured TMD: 2M-WSe₂ up to ~80 GPa through electrical transport and synchrotron x-ray diffraction (XRD) measurements. Superconductivity emerges at ~3.1 GPa, reaching the maximum around 8.9 GPa, and then disappears upon further compression. With the disappearance of superconductivity, an unexpected metal-semiconductor transition (MST) occurs around 14.6 GPa. The XRD results demonstrate that the MST can be attributed to the pressure-induced interlayer structural modulation to the monoclinic P2₁/m phase. Hall effect measurement reveals that the MST is accompanied by a decrease in hole-type carrier density. In addition, the final stable P2₁/m phase exhibits excellent metallic properties, but superconductivity does not re-emerge. It is very rare finding this metal-semiconductor transition in TMDs. Our result reveals the critical role of interlayer modulation under pressure in shaping the physical properties of TMDs and further expands the research field for layered materials.