Pressure-Induced Electronic Topological Transition and Superconducting Transition in Two-Dimensional Topological Insulator GeBi2Te4.

Owing to their topologically protected electronic states, layered van der Waals solids in binary and ternary chalcogenide families provide a fertile testbed for exploring unusual electronic and structural states, such as topological insulators and pressure-induced superconducting states. Herein, we report comprehensive high-pressure structural, Raman spectroscopic, and electrical transport investigations of the topological insulator GeBi2Te4 using diamond-anvil-cell techniques. Our experimental results show that pressure-induced superconductivity emerges in the initial trigonal R3̅m phase of GeBi2Te4, a compound known to possess topological-insulator features at ambient pressure. The pressure-induced superconductivity is enhanced with increasing pressure in this phase. In situ high-pressure Raman measurements reveal phonon anomalies around 2-3 GPa. These Raman anomalies occur in the same pressure range as the abnormal c/a response observed by XRD and are further supported by first-principles calculations, which reproduce a minimum in the calculated c/a ratio at 3-4 GPa. Together, these results provide multiprobe evidence for an ETT in the initial trigonal phase of GeBi2Te4. The concurrence of the ETT and superconducting onset within the same low-pressure phase suggests that electronic reconstruction may play an important role in pressure-induced superconductivity in this compound. This work provides a more detailed high-pressure picture of GeBi2Te4 and offers experimental insight into superconductivity emerging from a topological-insulator parent phase.