Two-Level Electronic Switching in Individual Manganese-Phthalocyanine Molecules with Jahn-Teller Distortion

Understanding single molecular switches is a crucial step in designing and optimizing molecular electronic devices with highly nonlinear functionalities, e.g., gate voltage-dependent current switching. An atomically thin insulating template, in combination with scanning probe techniques, is an ideal platform to study such switches on the single-molecule level. In this study, we investigate manganese-phthalocyanine (MnPc) molecules on monolayer-thin epitaxial hexagonal boron nitride (h-BN) on Rh(111) by scanning tunneling microscopy (STM), spectroscopy (STS), and theoretical calculations. Several interesting phenomena are found: (1) high-resolution STM imaging of the molecular orbitals reveals symmetry breaking from D_4h to D_2h, observed in one type of MnPc. By comparison with simulations, this phenomenon can be attributed to the Jahn-Teller effect due to the negative charging of the molecule. (2) Ambipolar transitions at the molecule occur at fixed sample biases of about ±0.4 V, which manifest as negative differential conductance signatures in dI/dV spectroscopy. (3) The stochastic two-level switching, resulting in telegraphic noise in the tunneling current, manifests as a one-electron activated process. We present a two-level switching model to accurately describe a bias-dependent current-driven transition between the levels and reveal a first-order transition. The understanding and tailoring of molecular switches on the ultrathin insulating layer will be very helpful for future organic electronics design and application.