Controlled switching of a single CuPc molecule on Cu(111) at low temperature

Low temperature measurements of the tunneling current as a function of the applied bias voltage have been performed on a dense constant-height grid above individual copper phthalocyanine molecules adsorbed on a Cu(111) surface. By appropriate tuning of the applied bias, the molecule can be reversibly switched between two configurations in which pairs of opposite maxima appear rotated by ${90}^{\ensuremath{\circ}}$ in the tunneling current map. The underlying conformations are revealed by density functional calculations including van der Waals interactions: a ${C}_2v$ symmetric ground state and two energetically equivalent states, in which the molecule is twisted and rotated around its center by $\ifmmode\pm\else\textpm\fi{}{7}^{\ensuremath{\circ}}$. For tip biases above 200 mV position-dependent current switching is observed, as in previous measurements of telegraph noise [Schaffert et al., Nat. Mater. 12, 223 (2013)]. In a small voltage interval around zero the measured current becomes bistable. Switching to a particular state can be initiated by sweeping the voltage past well-defined positive and negative thresholds at certain positions above the molecule or by scanning at constant current and a reduced reverse bias.