  We experimentally study the electrical transport properties of Ge/Si
core/shell nanowire device with two superconducting leads in the Coulomb
blockade regime. Anomalous zero field magnetoconductance peaks are observed for
the first time at the gate voltages where Coulomb blockade oscillation peaks
present. Many evidences indicate this feature is due to Andreev reflection
enhanced phase coherent single hole tunneling through the quantum dot, which
can be suppressed by an external magnetic field without destroying the
superconducting states in the electrodes.
