Tuning the charge density wave quantum critical point and the appearance of superconductivity in TiSe2

Abstract

The transition metal dichalcogenide $\mathrm{Ti}{\mathrm{Se}}_{2}$ is an ideal correlated system for studying the interplay between superconductivity (SC) and a charge density wave (CDW) because both symmetry-breaking phases can be easily controlled by either Cu intercalation or physical pressure. SC appears in proximity to a CDW quantum critical point (QCP) induced by both Cu intercalation and applied pressure, raising the possibility of CDW-driven SC. Here, we report tuning the CDW QCP by simultaneously controlling Cu intercalation and external pressure and the appearance of a SC dome centered on the tunable QCP. When subjected to pressure, CDW ordering of Cu-intercalated ${\mathrm{Cu}}_{0.025}\mathrm{Ti}{\mathrm{Se}}_{2}$ is completely suppressed at 2.3 GPa, where the residual resistivity and the resistivity-temperature exponent decrease sharply, indicating the presence of the CDW QCP. The upper critical field of ${\mathrm{Cu}}_{0.025}\mathrm{Ti}{\mathrm{Se}}_{2}$ is 3.51 kOe, 16 times larger than that of pristine $\mathrm{Ti}{\mathrm{Se}}_{2}$, and its temperature dependence is linear, indicating that SC of $\mathrm{Ti}{\mathrm{Se}}_{2}$ is switched from the two-dimensional- to anisotropic three-dimensional-like by Cu intercalation. These discoveries show that the simultaneous application of Cu intercalation and pressure move the CDW QCP and that the highest SC transition temperature is pinned to the QCP, suggesting that the SC in $\mathrm{Ti}{\mathrm{Se}}_{2}$ is strongly correlated with CDW quantum criticality.