Fig. 1: Ionic liquid gating-induced protonation: electric transport and structural characterization.
a Sketch of a TiSe2 crystal immersed in the electrochemical cell for ionic liquid gating-induced protonation, including the electrical connections. The side panel shows a ball-and-stick model of the HxTiSe2 structure with x ≲ 1. b Gate voltage VG and resistivity ρ(300 K) measured in situ as a function of time, during a typical gating sequence in the electrochemical cell at ambient conditions. The gating time (i.e., the time at which the crystal is kept at VG = + 3 V) is highlighted. c ρ(300 K) measured ex situ and (d), Hall carrier density nH at 4.2 K, of a series of TiSe2 crystals gated for increasing amounts of time. Error bars almost entirely arise from non-ideal sample geometry. Shaded gray bands are guides to the eye. e X-ray diffraction spectra in selected TiSe2 crystals at different gating times. The inset shows the resulting unit cell volume as a function of the gating time. f ρ as a function of temperature (T) for the same crystals reported in (c), normalized by the value at 300 K. The inset shows a magnification of the T range where the superconducting transitions are observed. g Raman spectra in ambient conditions acquired on the freshly-cleaved surfaces of a pristine TiSe2 (black curve) and a H2TiSe2 (red curve) crystal.
