Symmetry plays a vital role in determining properties of a system, and therefore, breaking the symmetry often gives rise to physical phenomena beyond the parent system. Here, we show that breaking rotational symmetry of an atomic collapse potential can induce intervalley scattering between states with different orbital angular momenta and result in an additional phase singularity around a supercritically charged vacancy in graphene. By using scanning tunneling microscopy, we directly detect transition of phase accumulation in the intervalley scattering from $4\pi$ outside the potential, contributed purely by pseudospin rotation, to $2\pi$ or $0\pi$ inside the potential, contributed by both the pseudospin rotation and nonzero angular momentum transfer. Moreover, in this study, we reveal that the anisotropic atomic collapse potential breaks the $C_3$ rotational symmetry of graphene and results in unexpected anisotropic interorbital angular momentum scatterings. Our observations establish a route to tune the quantum phase at atomic scale and highlight the role of breaking the symmetry in discovering emergent quantum phenomena in Dirac materials.

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• Point defects
• Valley degrees of freedom
• Graphene
• Scanning tunneling microscopy
• Scanning tunneling spectroscopy