81 research outputs found
Non-topological parafermions in a one-dimensional fermionic model with even multiplet pairing
We discuss a one-dimensional fermionic model with a generalized
even multiplet pairing extending Kitaev
chain. The system shares many features with models believed to host localized
edge parafermions, the most prominent being a similar bosonized Hamiltonian and
a symmetry enforcing an -fold degenerate ground state
robust to certain disorder. Interestingly, we show that the system supports a
pair of parafermions but they are non-local instead of being boundary
operators. As a result, the degeneracy of the ground state is only partly
topological and coexists with spontaneous symmetry breaking by a (two-particle)
pairing field. Each symmetry-breaking sector is shown to possess a pair of
Majorana edge modes encoding the topological twofold degeneracy. Surrounded by
two band insulators, the model exhibits for the dual of an
fractional Josephson effect highlighting the presence of parafermions.Comment: 12 pages, 3 figure
Floquet time crystal in the Lipkin-Meshkov-Glick model
In this work we discuss the existence of time-translation symmetry breaking
in a kicked infinite-range-interacting clean spin system described by the
Lipkin-Meshkov-Glick model. This Floquet time crystal is robust under
perturbations of the kicking protocol, its existence being intimately linked to
the underlying symmetry breaking of the time-independent model.
We show that the model being infinite-range and having an extensive amount of
symmetry breaking eigenstates is essential for having the time-crystal
behaviour. In particular we discuss the properties of the Floquet spectrum, and
show the existence of doublets of Floquet states which are respectively even
and odd superposition of symmetry broken states and have quasi-energies
differing of half the driving frequencies, a key essence of Floquet time
crystals. Remarkably, the stability of the time-crystal phase can be directly
analysed in the limit of infinite size, discussing the properties of the
corresponding classical phase space. Through a detailed analysis of the
robustness of the time crystal to various perturbations we are able to map the
corresponding phase diagram. We finally discuss the possibility of an
experimental implementation by means of trapped ions.Comment: 14 pages, 12 figure
Many-body localization dynamics from gauge invariance
We show how lattice gauge theories can display many-body localization
dynamics in the absence of disorder. Our starting point is the observation
that, for some generic translationally invariant states, Gauss law effectively
induces a dynamics which can be described as a disorder average over gauge
super-selection sectors. We carry out extensive exact simulations on the
real-time dynamics of a lattice Schwinger model, describing the coupling
between U(1) gauge fields and staggered fermions. Our results show how memory
effects and slow entanglement growth are present in a broad regime of
parameters - in particular, for sufficiently large interactions. These findings
are immediately relevant to cold atoms and trapped ions experiments realizing
dynamical gauge fields, and suggest a new and universal link between
confinement and entanglement dynamics in the many-body localized phase of
lattice models.Comment: 5Pages + appendices; V2: updated discussion in page 2, more numerical
results, added reference
Finite-density phase diagram of a (1+1)-d non-abelian lattice gauge theory with tensor networks
We investigate the finite-density phase diagram of a non-abelian SU(2)
lattice gauge theory in (1+1)-dimensions using tensor network methods. We
numerically characterise the phase diagram as a function of the matter filling
and of the matter-field coupling, identifying different phases, some of them
appearing only at finite densities. For weak matter-field coupling we find a
meson BCS liquid phase, which is confirmed by second-order analytical
perturbation theory. At unit filling and for strong coupling, the system
undergoes a phase transition to a charge density wave of single-site (spin-0)
mesons via spontaneous chiral symmetry breaking. At finite densities, the
chiral symmetry is restored almost everywhere, and the meson BCS liquid becomes
a simple liquid at strong couplings, with the exception of filling two-thirds,
where a charge density wave of mesons spreading over neighbouring sites
appears. Finally, we identify two tri-critical points between the chiral and
the two liquid phases which are compatible with a
Wess-Zumino-Novikov-Witten model. Here we do not perform the continuum limit
but we explicitly address the global charge conservation symmetry.Comment: 13 pages, 8 figure
Phase Diagram and Conformal String Excitations of Square Ice using Gauge Invariant Matrix Product States
We investigate the ground state phase diagram of square ice -- a U(1) lattice
gauge theory in two spatial dimensions -- using gauge invariant tensor network
techniques. By correlation function, Wilson loop, and entanglement diagnostics,
we characterize its phases and the transitions between them, finding good
agreement with previous studies. We study the entanglement properties of string
excitations on top of the ground state, and provide direct evidence of the fact
that the latter are described by a conformal field theory. Our results pave the
way to the application of tensor network methods to confining, two-dimensional
lattice gauge theories, to investigate their phase diagrams and low-lying
excitations.Comment: 36 pages, 16 figures; referee suggestions incorporated, added Figs.
3, 13 and appendices A,
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