Abstract:
The
Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO)
state
is
a
novel superconducting
state
in
a
strong
magnetic
field
characterized
by
the
formation
of
Cooper
pairs
with
nonzero
total
momentum (k,
-k+q), instead
of
the
ordinary
BCS
pairs
(k,
-k).
A
fascinating
aspect
of
the
FFLO
state
is
that
it
exhibits
inhomogeneous
superconducting
phases
with a
spatially
oscillating
order
parameter
and
spin
polarization.
The
FFLO
state
has
been
of
interest
in
various
research
fields,
not
only
in superconductors
in
solid
state
physics,
but
also
in
neutral
Fermion
superfluid
of
ultracold
atomic
gases
and
in
color
superconductivity
in high
energy
physics.
In
spite
of
extensive
studies
of
various
superconductors,
there
has
been
no
undisputed
experimental
verification of
the
FFLO
state,
mainly
because
of
the
very
stringent
conditions
required
of
the
superconducting
materials.
Among
several
classes
of materials,
certain
heavy
fermion
and
organic
superconductors
are
believed
to
provide
conditions
that
are
favorable
to
the
formation
of the
FFLO
state.
Here
I
discuss
recent
experimental
and
theoretical
developments
of
the
FFLO
state
mainly
in
heavy
fermion
superconductors.
In
particular
I
address
the
recently
discovered
quasi-two-dimensional
superconductor
CeCoIn5,
which
is
a
candidate
for
the
formation
of
the FFLO
state.