  Spatially varying strained graphene can acquire interesting electronic
properties because of the strain-induced valley-dependent gauge
(pseudomagnetic) fields1,2. Here we report the realization of strained graphene
regions located close to the step edges of Cu(111), obtained by using thermal
strain engineering3,4. We study these strained structures with
sub-nanometre-resolved scanning tunnelling microscopy and spectroscopy and
identify their spatially modulated Dirac points, demonstrating the effect of
overlap of Cu and graphene wave functions on the charge transfer between them5.
By applying a magnetic field of 8 Tesla, electron confinement, as revealed by
regularly spaced sharp resonances6,7, is observed in the strained graphene. In
some regions of the strained graphene, repetitive pairs of resonance peaks
appear in the tunnelling spectra. This provides direct and compelling evidence
for lifting of valley degeneracy due to the coexistence of both the magnetic
field and the pseudomagnetic field.
