  We report on a magneto-photoluminescence study of isotopically pure 70Ge/Si
self-assembled type-II quantum dots. Oscillatory behaviors attributed to the
Aharonov-Bohm effect are simultaneously observed for the emission energy and
intensity of excitons subject to an increasing magnetic field. When the
magnetic flux penetrates through the ring-like trajectory of an electron moving
around each quantum dot, the ground state of an exciton experiences a change in
its angular momentum. Our results provide the experimental evidence for the
phase coherence of a localized electron wave function in group-IV Ge/Si
self-assembled quantum structures.
