  By using a hydrostatic pressure, we have successfully tuned the ground state
and superconductivity in LaO0.5F0.5BiSe2 single crystals. It is found that,
with the increase of pressure, the original superconducting phase with Tc about
3.5 K can be tuned to a state with lower Tc, and then a new superconducting
phase with Tc about 6.5 K emerges. Accompanied by this crossover, the ground
state is switched from a semiconducting state to a metallic one. Accordingly,
the normal state resistivity also shows a nonmonotonic change with the external
pressure. Furthermore, by applying a magnetic field, the new superconducting
state under pressure with Tc about 6.5 K is suppressed, and the normal state
reveals a weak semiconducting feature again. These results illustrate a
non-trivial relationship between the normal state property and
superconductivity in this newly discovered superconducting system.

Superconductivity