Niobium titanium alloy is the most pressure-resistant superconductor

Recently, the State Key Laboratory of Superconductivity, Institute of Physics, Chinese Academy of Sciences/National Research Center for Condensed Matter Physics, Beijing, in collaboration with Princeton University, conducted a systematic study on the superconductivity of Nb-Ti alloy superconductors under ultra-high pressures. It is found that Nb-Ti alloy maintains zero resistance at pressures up to 261.7GPa, which indicates that Nb-Ti alloy is the most pressure-resistant superconductor among all known superconductors. This pressure is the highest reported for superconductivity. The transition temperature of Nb Ti alloy superconductor increases from 9.6K to 19.1K at normal pressure, and the critical magnetic field increases from 15.4T to 19T at 211GPa and 1.8K at high pressure and temperature in Hefei. This is the highest superconducting transition temperature and the highest critical magnetic field ever found in a transition metal elemental alloy superconductor. The results of synchrotron radiation high pressure XRD experiments with Shanghai light source show that the crystal structure does not change at 200 GPa, but the volume of the crystal is compressed by about 43%.

Niobium titanium alloy superconductors have been widely used in thousands of known superconductors due to their excellent comprehensive properties and are the key materials in superconducting magnets for medical NMR and large scientific devices. Niobium titanium alloy is a typical binary alloy composed of transition group elements. In the previous study on the high entropy alloy superconductor (TaNb)0.67(HfZrTi)0.33 composed of multiple transition metal elements, it was found that the alloy exhibited exceptionally stable superconductivity under ultra-high pressure (the pressure above one million atmospheres is ultra-high pressure, 1 million atmospheres =100 GPa). Since niobium and titanium are the main elements of the high entropy alloy, the understanding of the microcosmic mechanism of superconductivity of the high entropy alloy can be enhanced by studying the superconductivity of niobium titanium alloy under ultra-high pressure.

The above studies reveal that the superconductivity of alloy superconductors composed of transition metal elements is stable and can resist large deformation under high pressure, which forms a sharp contrast with the high sensitivity of the superconductivity of copper oxide and iron based superconductors to volume changes. It is also different from the behavior that the superconducting transition temperature of the post-transition metal element superconductor (D-electron full shell in valence state electron) decreases with volume compression. This study successfully combines the experiments of high pressure extreme conditions, strong magnetic field and synchrotron radiation in large scientific equipment, and provides a new example for China to use its own large scientific equipment to jointly carry out frontier scientific research.