  Anomalously large fluctuation diamagnetism around the superconducting
critical temperature has been recently observed on iron selenide (FeSe) [S.
Kasahara et al., unpublished]. This indicates that superconducting fluctuations
(SCFs) play a more significant role in FeSe, which supposedly has two-band
structure, than in the familiar single-band superconductors. Motivated by the
data in FeSe, SCF-induced diamagnetism is examined in a two-band system, on the
basis of a phenomenological approach with a Ginzburg-Landau functional. The
obtained results indicate that the SCF-induced diamagnetism may be more
enhanced than that in a single-band system due to the existence of two distinct
fluctuation modes. Such enhancement of diamagnetism unique to a two-band system
seems consistent with the large diamagnetism observed on FeSe, though still far
from a quantitative agreement.
