  Metallization of quantum spin liquid (QSL) materials has long been considered
as a potential route to achieve unconventional superconductivity. Here we
report our endeavor in this direction by pressurizing a three-dimensional QSL
candidate, LiYbSe$_2$, with a previously unreported pyrochlore structure.
High-pressure X-ray diffraction and Raman studies up to 50 GPa reveal no
appreciable changes of structural symmetry or distortion in this pressure
range. This compound is so insulating that its resistance decreases below
10$^5$ ${\Omega}$ only at pressures above 25 GPa in the corresponding
temperature range accompanying the gradual reduction of band gap upon
compression. Interestingly, an insulator-to-metal transition takes place in
LiYbSe$_2$ at about 68 GPa and the metallic behavior remains up to 123.5 GPa,
the highest pressure reached in the present study. A possible sign of magnetic
or other phase transition was observed in LiYbSe$_2$. The insulator-to-metal
transition in LiYbSe$_2$ under high pressure makes it an ideal system to study
the pressure effects on QSL candidates of spin-1/2 Yb$^{3+}$ system in
different lattice patterns.
