Observation of pressure-induced superconductivity in WB₂

High-pressure electrical resistivity measurements reveal that the mechanical deformation of ultra-hard WB₂ during compression induces superconductivity above 50 GPa with a maximum superconducting critical temperature, T_c of 17 K at 90 GPa [1]. Upon further compression up to 190 GPa, the T_c gradually decreases to 14 K at a rate of -0.024 K/GPa. We investigate the presence of MgB₂-like structural transition (hP3, space group 191, prototype AlB2) in WB₂ under pressures, which might be responsible for the relatively high T_c superconductivity as recently found in MoB₂ [2]. Synchrotron x-ray diffraction measurements up to 145 GPa at room temperature show that the ambient pressure hP12 structure (space group 194, prototype WB₂) continues to persist to this pressure without any structural transition. Thus, these experimental results indicate the novel origin of the abrupt appearance of superconductivity in WB₂ under pressures above 50 GPa. In the following talk, we show that electron-phonon mediated superconductivity in WB₂ originates from the formation of metastable stacking faults and twin boundaries that exhibit a local structure resembling the MgB₂ structure.