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 (T c = 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 T c in the intercalated NbSe2 sample, and qualitatively explain the variation of T c 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.