Emergence of superconductivity near 11 K by suppressing the 3-fold helical-chain structure in noncentrosymmetric HgS

Abstract

The trigonal ${\alpha}$-HgS has a 3-fold helical chain structure, and is in form of a noncentrosymmetric $P3_121$ phase, known as the cinnabar phase. However, under pressure, the helical chains gradually approach and connect with each other, finally reconstructing into a centrosymmetric NaCl structure at 21 GPa. Superconductivity emerges just after this helical-nonhelical structural transition. The maximum critical temperature ($T_c$) reaches 11 K at 25.4 GPa, $T_c$ decreases with further compression, and is still 3.5 K at 44.8 GPa. Furthermore, the $T_c$-critical magnetic field ($B_{c2}$) relation exhibits multi-band features, with a $B_{c2}$ of 5.65 T at 0 K by two-band fitting. Raman spectra analysis demonstrates that phonon softening plays a key role in structural transition and the emergence of superconductivity. It is noted that HgS is the first reported IIB group metal sulfide superconductor and the only NaCl-type metal sulfide superconductor with a $T_c$ above 10 K. This work will inspire the exploration of superconductivity in other chiral systems and will extend our understanding of the versatile behavior in such kinds of materials.