  We study the observability of the Higgs mode in BEC-BCS crossover. The
observability of Higgs mode is investigated by calculating the spectral weight
functions of the amplitude fluctuation below the critical transition
temperature. At zero temperature, we find that there are two sharp peaks on the
spectral function of the amplitude fluctuation attributed to Goldstone and
Higgs modes respectively. As the system goes from BCS to BEC side, there is
strong enhancement of spectral weight transfer from the Higgs to Goldstone
mode. However, even at the unitary regime where the Lorentz invariance is lost,
the sharp feature of Higgs mode still exists. We specifically calculate the
finite temperature spectral function of amplitude fluctuation at the unitary
regime and show that the Higgs mode is observable at the temperature that
present experiments can reach.
