High-Pressure Investigations of the Structural and Electronic Properties of the Three-Dimensional Topological Insulator Candidate Ni₃Bi₂Se₂

Ni₃Bi₂Se₂is a bismuth-containing layered compound recently proposed to host nontrivial topological electronic states and has been reported to exhibit superconductivity below 0.7 K. Exploring the possible enhancement of this superconductivity through external parameters, such as pressure, will be important for assessing its potential as a topological superconductor. We present high-pressure studies of its structural and electronic properties up to ∼22 GPa, combining synchrotron X-ray diffraction (S-XRD), transport measurements, and first-principles calculations. No superconducting transition is observed above 2 K across the entire pressure range. X-ray diffraction (XRD) shows that the ambient-pressure monoclinic structure remains stable up to 22 GPa whereas transport measurements reveal a monotonic increase in the Debye temperature and a simultaneous decrease in carrier density under pressure. Density functional theory (DFT) calculations support these findings, showing a reduction in the density of states at the Fermi level and the persistence of the nontrivial topological Z2 index (1;111) up to 21 GPa. The absence of superconductivity enhancement in Ni₃Bi₂Se₂is attributed primarily to the reduced density of states, which weakens electron–phonon coupling. These results underscore the crucial role of electronic structure tuning, beyond structural stability, in the pursuit of topological superconductivity under pressure.