Search for high-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>T</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math>conventional superconductivity at megabar pressures in the lithium-sulfur system

Abstract

Superconductivity at high-pressures has attracted considerable interest after the report of a record critical temperature (${T}_{c}$) of 203 K in sulfur hydride (H${}_{3}$S) at 200 GPa. In this work, the authors predict several novel lithium-sulfur compounds at high pressure using evolutionary crystal structure prediction techniques and investigate their superconducting properties with density functional linear response calculations. The calculations reveal an intrinsic correlation between superconductivity and real-space electron localization. We find that high-${T}_{c}$ superconductivity in the Li-S system occurs at pressures much higher than in H${}_{3}$S, i.e., only when the electrode-like interstitial charge localization typical of alkali-metal compounds is suppressed. This is illustrated in the image, which shows a comparison of the electron-phonon spectral function ${\ensuremath{\alpha}}^{2}\phantom{\rule{0}{0ex}}F(\ensuremath{\omega})$ of Li${}_{3}$S in the low- pressure (panel $a$, ${T}_{c}=0$ K) and high-pressure phases (panel $c$, ${T}_{c}=80$ K), calculated at 500 GPa. The right panels of the image show that the increase in ${T}_{c}$ is accompanied by a shift of the electronic charge from $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ regions to Li-S bonds.