Tunable Superconductivity in 2H-NbSe2 via in situ Li Intercalation

Abstract

Using the newly-developed solid ionic gating technique, we measure the electrical transport property of a thin-flake NbSe2 superconductor (Tc = 6.67 K) under continuous Li intercalation and electron doping. It is found that the charge-density-wave transition is suppressed, while at the same time a carrier density, decreasing from 7 × 1014 cm–2 to 2 × 1014 cm–2 also occurs. This tunable capability in relation to carrier density is 70%, which is 5 times larger than that found using the liquid ionic gating method [Phys. Rev. Lett. 117 (2016) 106801]. Meanwhile, we find that the scattering type of conduction electrons transits to the s–d process, which may be caused by the change of the occupied states of 4d-electrons in Nb under the condition of Li intercalation. Simultaneously, we observe a certain decrement of electron-phonon coupling (EPC), based on the electron-phonon scattering model, in the high temperature range. Based on data gathered from in situ measurements, we construct a full phase diagram of carrier density, EPC and Tc in the intercalated NbSe2 sample, and qualitatively explain the variation of Tc within the BCS framework. It is our opinion that the in situ solid ionic gating method provides a direct route to describing the relationship between carrier density and superconductivity, which is helpful in promoting a clearer understanding of electronic phase competition in transition metal dichalcogenides.