Superconducting gap and its Little-Parks like oscillations in lithium intercalated 1T-TiSe₂

Ions intercalation has emerged as an important technique for tuning two-dimensional materials in recent years. We have developed a lateral intercalation technique via solid ion backgating to enhance the homogeneity [1], and employed this technique to tune the critical magnetic field of layered NbSe₂ [2] and superconducting networks in TiSe₂. TiSe₂ is an interesting platform that hosts many collective quantum phenomena, including the charge density wave (CDW), a gyrotropic electronic order, and superconductivity under high pressure or after electrostatic chemical doping. We have tuned TiSe₂ to superconducting states by intercalating lithium, and observed magnetoresistance oscillations and anomalous metal states under magnetic fields. We obtained the superconducting gap of Li_𝑥TiSe₂ via tunneling measurements. The gap closing temperature of Li_𝑥TiSe₂ is higher than that estimated based on the Bardeen-Cooper-Schrieffer (BCS) theory, indicating strong fluctuations in the superconducting state. In the anomalous metal state, the superconducting gap of Li_𝑥TiSe₂ exhibits periodic oscillations under magnetic fields. These oscillations are related to two-dimensional structures and can be tuned by lithium doping. This suggests that Li_𝑥TiSe₂ forms a superconducting texture, and Little-Parks effect leads to gap oscillations. Moreover, the oscillations manifest higher harmonics, indicating a highly regular structure. Our work opens a distinct pathway to address emergent phenomena under in-situ ion gating.

[1] Jia-Yi Ji et al. Homogeneous lateral lithium intercalation into transition metal dichalcogenides via ion backgating. Nano Letters 22, 7336 (2022).

[2] Jia-Yi Ji et al. Continuous tuning of spin-orbit coupled superconductivity in NbSe₂. Physical Review B 110, 104509 (2024).