  We study the lead rhenium oxide PbRe2O6 as a candidate spin-orbit-coupled
metal (SOCM), which has attracted much attention as a testing ground for
studying unconventional Fermi liquid instability associated with a large
spin-orbit interaction. The compound comprises a stack of modulated honeycomb
lattices made of Re5+ (5d2) ions in a centrosymmetric R-3m structure at room
temperature. Resistivity, magnetic susceptibility, and heat capacity
measurements using single crystals reveal two successive first-order phase
transitions at Ts1 = 265 K and Ts2 = 123 K. At Ts1, the magnetic susceptibility
is enormously reduced and a structural transition to a monoclinic structure
takes place, while relatively small changes are observed at Ts2. Surprisingly,
PbRe2O6 bears a close resemblance to another SOCM candidate Cd2Re2O7 despite
crucial differences in the crystal structure and probably in the electronic
structure, suggesting that PbRe2O6 is an SOCM.
