The massless Dirac fermions and the ease to introduce spatial and magnetic confinement in graphene provide us unprecedented opportunity to explore confined relativistic matter in this condensed-matter system. Here we report the interplay between the confinement induced by external electric fields and magnetic fields of the massless Dirac fermions in graphene. When the magnetic length $l_B$ is larger than the characteristic length of the confined electric potential $l_V$, the spatial confinement dominates and a relatively small critical magnetic field splits the spatial-confinement induced atomiclike shell states by switching on a π Berry phase of the quasiparticles. When the $l_B$ becomes smaller than the $l_V$, the transition from spatial confinement to magnetic confinement occurs and the atomiclike shell states condense into Landau levels (LLs) of the Fock-Darwin states in graphene. Our experiment demonstrates that the spatial confinement dramatically changes the energy spacing between the LLs and generates large electron-hole asymmetry of the energy spacing between the LLs. These results shed light on puzzling observations in previous experiments, which hitherto remained unaddressed.

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• Confinement
• Dirac fermions
• Graphene
• Scanning tunneling microscopy
• Scanning tunneling spectroscopy