Fig. 1: A selenium vacancy (VacSe) in few-layer WSe2 as a single atom quantum dot.
From: Ultrafast Coulomb blockade in an atomic-scale quantum dot
a Illustration of the experiment: VacSe in two monolayer (2 ML) WSe2 on quasi free standing epitaxial graphene (QFEG) and conductive SiC studied with lightwave-driven STM. Free-space propagating THz pulses induce transient voltage bursts at the STM tip that enable electron tunneling into localized defect states of VacSe. b Energy diagram illustrating electron tunneling from the tip to the VacSe in a double-barrier model, where the Fermi level (EF) is pinned by the QFEG substrate. The electron transfer depends on the different coupling strengths Γ, which are based on energy (voltage) differences, the tip-sample spacing z and the WSe2 layer thickness d that determines the coupling of VacSe to the tip (T) and the substrate (S), respectively. The charge occupation at VacSe exponentially relaxes to its equilibrium state. c Schematic representation of sequential electron tunneling depicted as an equivalent circuit. The time-dependent tip voltage bias (Vt) is the sum of: (i) constant Vdc, and (ii) single THz voltage pulse with peak amplitude \({V}_{{{{\rm{THz}}}}}^{{{{\rm{pk}}}}}\), or (iii) pump and probe THz pulses with individual amplitude and time delay Δt.
