Super-Earths have solid cores

The high melting temperatures and the large viscosities that we've calculated for super-Earths suggest either a slow core formation or no core formation at all. This raises doubts about whether super-Earths could generate magnetic fields," said Stamenkovic.

Even if those super-Earths are differentiated, the research indicates that convection would be sluggish or that stagnant layers could form deep in the mantle, putting an effective lid on heat flow from the core. Strongly depending on the initial conditions, conduction may become the dominant form of heat transport. This would reduce the cooling rate of the core, again potentially quashing dynamo action.

The team has found the propensity of plate tectonics to rather decline with planetary mass. But they also find that water in the lithosphere can easily buffer these effects. Hence plate tectonics on super-Earths is not inevitable, but rather depends on a set of unknown planetary characteristics, which can’t be observed on exoplanets in the near future.