Record high Tc element superconductivity achieved in titanium

Abstract

It is challenging to search for high T_c superconductivity (SC) in transition metal elements wherein d electrons are usually not favored by conventional BCS theory. Here we report experimental discovery of surprising SC up to 310 GPa with T_c above 20 K in wide pressure range from 108 GPa to 240 GPa in titanium. The maximum T_c^onset above 26.2 K and zero resistance T_c^zero of 21 K are record high values hitherto achieved among element superconductors. The H_c2(0) is estimated to be ∼32 Tesla with coherence length 32 Å. The results show strong s-d transfer and d band dominance, indicating correlation driven contributions to high T_c SC in dense titanium. This finding is in sharp contrast to the theoretical predications based on pristine electron-phonon coupling scenario. The study opens a fresh promising avenue for rational design and discovery of high T_c superconductors among simple materials via pressure tuned unconventional mechanism.