  Heat capacity measurements on the recently discovered geometrically
frustrated beta-pyrochlore superconductor RbOs2O6 (Tc=6.4 K) yield a Sommerfeld
coefficient of 44 mJ/(molf.u. K^2). This is about 4 times larger than the one
found in band structure calculations. In order to specify the enhancement due
to electron-electron interactions, we have measured the electron-phonon
enhancement. By a suitable analysis, an electron-phonon coupling constant
lambda_ep = 1 +/- 0.1 is derived from the specific heat jump at Tc. This leaves
a significant additional lambda_add = 2.1 +/- 0.3 for enhancement due to other
mechanisms, possibly related to the triangular lattice. To arrive at these
results, an appropriate analysis method for bulk thermodynamic data based on
the condensation energy was applied.
