  The interaction between electrons in graphene under high magnetic fields
drives the formation of a rich set of quantum Hall ferromagnetic phases (QHFM),
with broken spin or valley symmetry. Visualizing atomic scale electronic
wavefunctions with scanning tunneling spectroscopy (STS), we resolve
microscopic signatures of valley ordering in QHFM and fractional quantum Hall
phases of graphene. At charge neutrality, we observe a field-tuned continuous
quantum phase transition from a valley polarized state to an intervalley
coherent state, with a Kekule distortion of its electronic density. Mapping the
valley texture extracted from STS measurements of the Kekule phase, we
visualize valley skyrmion excitations localized near charged defects. Our
techniques can be applied to examine valley ordered phases and their
topological excitations in a wide range of materials.
