  We report on quantum transport measurements on etched graphene nanoribbons
encapsulated in hexagonal boron nitride (hBN). At zero magnetic field our
devices behave qualitatively very similar to what has been reported for
graphene nanoribbons on $\text{SiO}_2$ or hBN, but exhibit a considerable
smaller transport gap. At magnetic fields of around $3~$T the transport
behavior changes considerably and is dominated by a much larger energy gap
induced by electron-electron interactions completely suppressing transport.
This energy gap increases with a slope on the order of $3-4~ $meV/T reaching
values of up to $ 30~\mathrm{meV} $ at $ 9~ $T.
