Fig. 3: Ultrafast modulation of the LDOS of a single defect.
From: Ultrafast atomic-scale scanning tunnelling spectroscopy of a single vacancy in a monolayer crystal
a, Tunnelling current driven by the THz probe pulse, \({I}_{{\rm{LW}}}^{{\rm{pr}}}\), as a function of delay time after a local THz pump pulse excitation (inset) exhibits oscillations on the defect orbital lobe (position highlighted as a white dot in b (right)). Pump and probe peak fields are 0.33E0 and 0.60E0 (that is, 990 mV and 1.80 V), respectively. b, Dependence of the amplitude A of oscillations in \({I}_{{\rm{LW}}}^{{\rm{pr}}}\) normalized by its mean value \({\left\langle {I}_{{\rm{LW}}}^{{\rm{pr}}}\right\rangle }_{{\rm{\tau }}}\) on the STM tip position relative to the vacancy (cross) (right panel) (constant-current STM image: V = 380 mV, I = 49 pA; colour bar, minimum to maximum apparent height). The peak pump (0.175E0, 525 mV) and probe field (0.300E0, 900 mV) were kept fixed. The data are shown as amplitude of the sinusoidal fit to oscillations in \({I}_{{\rm{LW}}}^{{\rm{pr}}}\) divided by \({\left\langle {I}_{{\rm{LW}}}^{{\rm{pr}}}\right\rangle }_{{\rm{\tau }}}\) ± 95% confidence margin of the amplitude fit. c, Ultrafast tunnelling spectra measured at the maximum (8.8 ps; red circle in a) and the minimum (10.2 ps; yellow circle in a) of the pump-induced oscillations (pump field: 0.32E0, 960 mV) recorded on the orbital lobe (white dot in b). On the top/bottom horizontal axis, the unattenuated far-field amplitude E0 is gauged to a peak voltage \({V}_{{\rm{LW}}}^{\,{\rm{peak}}}\) of 3 V. The inset shows the fixed pump–variable probe scheme for the measurement of time-resolved ultrafast tunnelling spectra. Data in a and c and \({I}_{{\rm{LW}}}^{{\rm{pr}}}\) used in b represent mean values ± standard deviations of bootstrapped datasets (Methods). Data in a include 12 measurements per point, each measurement containing 18.3 million laser pulses. Data in b comprise nine measurements of \({I}_{{\rm{LW}}}^{{\rm{pr}}}\) per delay and position each, and involve 109.8 million laser pulses. Data in c include 11 (13 and 10) measurements for 8.8 ps (10.2 ps and unpumped) per delay and peak voltage each, and involve 219.6 million laser pulses per measurement.
