Title: Thermal transitions, pseudogap behavior and BCS-BEC crossover in Fermi-Fermi mixtures,
Abstract: We study the mass imbalanced Fermi-Fermi mixture within the framework of a
two-dimensional lattice fermion model. Based on the thermodynamic and species
dependent quasiparticle behavior we map out the finite temperature phase
diagram of this system and show that unlike the balanced Fermi superfluid there
are now two different pseudogap regimes as PG-I and PG-II. While within the
PG-I regime both the fermionic species are pseudogapped, PG-II corresponds to
the regime where pseudogap feature survives only in the light species. We
believe that the single particle spectral features that we discuss in this
paper are observable through the species resolved radio frequency spectroscopy
and momentum resolved photo emission spectroscopy measurements on systems such
as, 6$_{Li}$-40$_{K}$ mixture. We further investigate the interplay between the
population and mass imbalances and report that at a fixed population imbalance
the BCS-BEC crossover in a Fermi-Fermi mixture would require a critical
interaction (U$_{c}$), for the realization of the uniform superfluid state. The
effect of imbalance in mass on the exotic Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) superfluid phase has been probed in detail in terms of the thermodynamic
and quasiparticle behavior of this phase. It has been observed that in spite of
the s-wave symmetry of the pairing field a nodal superfluid gap is realized in
the LO regime. Our results on the various thermal scales and regimes are
expected to serve as benchmarks for the experimental observations on
6$_{Li}$-40$_{K}$ mixture.