  Materials exhibiting reversible resistive switching in electrical fields are
highly demanded for functional elements in oxide electronics. In particular,
multilevel switching effects allow for advanced applications like neuromorphic
circuits. Here we report on a structurally driven switching mechanism involving
the so-called `dead layers' of perovskite manganite surfaces. Forming a tunnel
barrier whose thickness can be changed in monolayer steps by electrical fields,
the switching effect exhibits well-defined and robust resistive states.
