Controlled melting of a Wigner ion crystal with atomic resolution

The solid-liquid phase transition (melting) is a long-standing problem for which a complete understanding is challenging because of the strong many-body interactions. A trapped-ion Wigner crystal is a suitable platform for a controlled study of this phase transition with its unprecedented resolution of individual atomic ions. Here we study the melting dynamics of a linear chain of $^{174}\mathrm{Yb}^{+}$ ions, which is initially cooled to the Doppler temperature and is then periodically heated and detected by a focused laser beam. We achieve controlled melting of the ion chain and observe unusual partial melting of long chains (coexistence of solid and liquid phases). We also observe a counterintuitive nonuniform energy distribution over the chain under localized heating. These results are further confirmed by molecular dynamics simulations to rule out other heating mechanisms.