Speaker
Prof.
Päivi Törmä
(Aalto University)
Description
We propose a mixed-geometry system of fermionic
species selectively confined in lattices of different
geometry [1]. We investigate how such asymmetry can
lead to exotic multiband fermion pairing in an example
system of honeycomb and triangular lattices. A rich
phase diagram of interband pairing with gapped and
gapless excitations is found at zero temperature. We
find that the two-band contribution of the honeycomb
lattices to the paired state helps to stabilize the
gapless phase with one or two Fermi surfaces. We also
show that the Fermi surface topology further divides
the gapless phase into subclasses between which the
system undergoes density-driven Lifshitz transitions.
We consider examples of interesting quantum dynamics
of interacting fermions in a one-dimensional system
(tube) with a lattice potential along the tube direction.
We have applied the time-dependent DMRG method,
and the Bethe ansatz in the strong interaction regime,
to exactly simulate and qualitatively describe the
dynamics. In particular, we characterize the expansion
of a band-insulator state in and show how it can be
understood in terms of two-site physics [2]. By similar
studies, we have shown that the Fulde-Ferrell-Larkin-
Ovchinnikov (FFLO) state is directly manifested in the
expansion dynamics [3]. We have studied the stability
of the FFLO state in the 1D-3D crossover [4]. We also
discuss dynamics of an impurity in a one-dimensional
Fermi gas which reveals a rich interplay of polaronic-
type and bound-pair effects [5].
[1] D.-H. Kim, J.S.J. Lehikoinen, and P. Törmä,
Topological transitions of gapless paired states in
mixed-geometry lattices, accepted to Phys. Rev. Lett.
(2013), arXiv:1209.1571.
[2] J. Kajala, F. Massel, and P. Törmä, Expansion
dynamics in the one-dimensional Fermi-Hubbard model,
Phys. Rev. Lett. 106, 206401 (2011).
[3] J. Kajala, F. Massel, and P. Törmä, Expansion
dynamics of the Fulde-Ferrell-Larkin-Ovchinnikov state,
Phys. Rev. A 84, 041601(R) (2011).
[4] D.-H. Kim and P. Törmä, Fulde-Ferrell-Larkin-
Ovchinnikov state in the dimensional crossover
between one- and three-dimensional lattices, Phys.
Rev. B 85, 180508(R) (2012).
[5] F. Massel, A. Kantian, A.D. Daley, T. Giamarchi, and
P. Törmä, Dynamics of an impurity in a one-dimensional
lattice, submitted to New J. Phys. (2012),
arXiv:1210.4270.
Primary author
Prof.
Päivi Törmä
(Aalto University)
