  Since their experimental discovery in 1989, the electron-doped cuprate
superconductors have presented both a major challenge and a major opportunity.
The major challenge has been to determine whether these materials are
fundamentally different from or essentially similar to their hole-doped
counterparts; a major opportunity because answering this question would
strongly constrain the possible explanations for what is the essential physics
that leads to high temperature superconductivity in the cuprates, which is
still not agreed upon. Here we argue that experimental results over the past 30
years on electron-doped cuprate materials have provided conclusive answers to
these fundamental questions, by establishing that both in hole- and
electron-doped cuprates, superconductivity originates in pairing of hole
carriers in the same band. We discuss a model to describe this physics that is
different from the generally accepted ones, and calculate physical observables
that agree with experiment, in particular tunneling characteristics. We argue
that our model is simpler, more natural and more compelling than other models.
Unlike other models, ours was originally proposed before rather than after many
key experiments were performed.
