Superconductivity emerging upon Se doping of the quantum spin liquid 1T−TaS2

Abstract

Paradigmatic quantum spin liquid has been in the past closely linked to the high-temperature superconductivity. Here we focus on a layered 1T-${\mathrm{TaS}}_{2}$, which has recently emerged as a surprising candidate for a quantum spin liquid on a triangular lattice. Upon doping 1T-${\mathrm{TaS}}_{2}$ with Se, the $^{77}\mathrm{Se}$ nuclear magnetic resonance and $^{181}\mathrm{Ta}$ nuclear quadrupole resonance data show a remarkable robustness of the quantum spin liquid at low Se doping levels despite the growth of inhomogeneities in the electronic state. A dramatic change in the low-energy electronic excitations are observed in samples with a moderate Se content where the Mott insulating state gives way to a correlated metal and a low-temperature superconductivity. The effects of antiferromagnetic correlations can still be traced in the normal state above the superconducting critical temperature ${T}_{\mathrm{c}}=3.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and may, together with the underlying disorder, account for the large superconducting gap-to-${T}_{\mathrm{c}}$ ratio $2\mathrm{\ensuremath{\Delta}}/{k}_{\mathrm{B}}{T}_{\mathrm{c}}\ensuremath{\approx}7$ deduced from the scanning tunneling microscopy.