Superconducting Gap and Its Little-Parks-like Oscillations with High-Order Harmonics in Lithium Intercalated 1T-TiSe₂.

Abstract

The superconducting phase of doped 1T-TiSe₂ is a fruitful playground for exploring exotic quantum phenomena such as the anomalous metal state and the spontaneously formed superconducting network. Here, we address these emergent states by studying the superconducting gap of lithium intercalated TiSe₂─a fundamental quantity that has remained unexplored so far. We fabricated a device that combines solid-state lateral lithium intercalation, resistance measurements, and tunneling spectroscopy. We successfully probed the superconducting gap of TiSe₂ and revealed that the gap closing temperature well exceeds the transition temperature (<i>T</i>_c) expected from the Bardeen-Cooper-Schrieffer theory, indicating pronounced superconducting fluctuations even in a bulk-like system. Moreover, the symmetric gap persists even in the anomalous metal state, demonstrating the particle-hole symmetry of this exotic phase directly from the density of states. Finally, the superconducting gap shows magneto-oscillations with high-order harmonics, attesting to a rather regular structure of the intrinsic superconducting network.