Fig. 4: Pump-field-dependent transient level shift and ultrafast dynamics.
From: Ultrafast atomic-scale scanning tunnelling spectroscopy of a single vacancy in a monolayer crystal
a,b, Ultrafast tunnelling spectra of the Se vacancy (measurement position shown in the inset) measured at delay times of τ = 10.2 ps (a) and τ = 8.8 ps (b) with different THz pump-field strengths (the legend shown in b applies to the data in all panels). The data for 10.2 ps reveal a distinct monotonic field-dependent shift in the tunnelling onset into the first defect level, whereas for τ = 8.8 ps, the energy shift occurs for low pump fields only (0.050E0 and 0.175E0). c, Oscillations in probe current \({I}_{{\rm{LW}}}^{{\rm{pr}}}-{{\langle I}_{{\rm{LW}}}^{{\rm{pr}}}\rangle }_{{\rm{\tau }}}\) for the three pump fields as a function of delay time (probe field, 0.32E0, 960 mV). The inset shows the structural peak-to-peak displacement as a function of the pump field, extracted from the oscillations in probe current using the exponential dependence of \({I}_{{\rm{LW}}}^{{\rm{pr}}}\) on the tip–sample distance (Extended Data Fig. 6). Data in a–c represent mean values ± standard deviations of the bootstrapped datasets (Methods). Three (five) (data in a) and five (five) (data in b) measurements per data point for pump fields of 0.175E0 (0.050E0); for 0.320E0, see Fig. 3c. Each measurement involves 219.6 million laser pulses. In c, \({I}_{{\rm{LW}}}^{{\rm{pr}}}\) comprises 18 (54) measurements for 0.175E0 and 0.320E0 (0.050E0) per delay each: 36.6 million laser pulses are used per measurement.
