  The 5/2 fractional quantum Hall effect in the second Landau level of
extremely clean two-dimensional electron gases has attracted much attention due
to its topological order predicted to host quasiparticles that obey non-Abelian
quantum statistics and could serve as a basis for fault-tolerant quantum
computations. While previous works have establish the Fermi liquid (FL) nature
of its putative composite fermion (CF) normal phase, little is known regarding
its thermodynamics properties and as a result its effective mass is entirely
unknown. Here, we report on time-resolved specific heat measurements at filling
factor 5/2, and we examine the ratio of specific heat to temperature as a
function of temperature. Combining these specific heat data with existing
longitudinal thermopower data measuring the entropy in the clean limit we find
that, unless a phase transition/crossover gives rise to large specific heat
anomaly, both datasets point towards a large effective mass in the FL phase of
CFs at 5/2. We estimate the effective-to-bare mass ratio m*/me to be ranging
from ~2 to 4, which is two to three times larger than previously measured
values in the first Landau level.
