  We report the basic thermodynamic properties of the new geometrically
frustrated beta-pyrochlore bulk superconductor RbOs2O6 with a critical
temperature Tc = 6.4 K. Specific heat measurements are performed in magnetic
fields up to 12 T. The electronic density of states at the Fermi level in the
normal state results in gamma = (33.7 \pm 0.2) mJ/mol_f.u./K^2. In the
superconducting state, the specific heat follows conventional BCS-type behavior
down to 1 K, i.e. over three orders of magnitude in specific heat data. The
upper critical field slope at Tc is 1.2 T/K, corresponding to a Maki-parameter
alpha = 0.64 \pm 0.1. From the upper critical field mu0 Hc2 \approx 6 T at 0 K,
we estimate a Ginzburg-Landau coherence length xi \approx 7.4 nm. RbOs2O6 is
the second reported metallic AB2O6 type pyrochlore compound after KOs2O6, and
one of only three pyrochlore superconductors in addition to Cd2Re2O7 and
KOs2O6.
