1,699 research outputs found
Topological phase in one-dimensional interacting fermion system
We study a one-dimensional interacting topological model by means of exact
diagonalization method. The topological properties are firstly examined with
the existence of the edge states at half-filling. We find that the topological
phases are not only robust to small repulsive interactions but also are
stabilized by small attractive interactions, and also finite repulsive
interaction can drive a topological non-trivial phase into a trivial one while
the attractive interaction can drive a trivial phase into a non-trivial one.
Next we calculate the Berry phase and parity of the bulk system and find that
they are equivalent in characterizing the topological phases. With them we
obtain the critical interaction strengths and construct part of the phase
diagram in the parameters space. Finally we discuss the effective Hamiltonian
at large-U limit and provide additional understanding of the numerical results.
Our these results could be realized experimentally using cold atoms trapped in
the 1D optical lattice.Comment: 7 pages, 5 figures; revised version, references added, Accepted for
publication in Physical Review
Observational Constraints on Secret Neutrino Interactions from Big Bang Nucleosynthesis
We investigate possible interactions between neutrinos and massive scalar
bosons via (or massive vector bosons via
) and explore the allowed
parameter space of the coupling constant (or ) and the
scalar (or vector) boson mass (or ) by requiring that these
secret neutrino interactions (SNIs) should not spoil the success of Big Bang
nucleosynthesis (BBN). Incorporating the SNIs into the evolution of the early
Universe in the BBN era, we numerically solve the Boltzmann equations and
compare the predictions for the abundances of light elements with observations.
It turns out that the constraint on and in the
scalar-boson case is rather weak, due to a small number of degrees of freedom.
However, in the vector-boson case, the most stringent bound on the coupling
at confidence level is obtained for
, while the bound becomes much weaker for smaller masses . Moreover, we discuss in some detail how the SNIs affect the cosmological
evolution and the abundances of the lightest elements.Comment: 18 pages, 5 figure
Fractional topological phase in one-dimensional flatbands with nontrivial topology
We show the existence of the fractional topological phase (FTP) in a
one-dimensional interacting fermion model using exact diagonalization, in which
the non-interacting part has flatbands with nontrivial topology. In the
presence of the nearest-neighbouring interaction , the FTP at filling
factor appears. It is characterized by the three-fold degeneracy and
the quantized total Berry phase of the ground-states. The FTP is destroyed by a
next-nearest-neighbouring interaction and the phase diagrams in the
plane is determined. We also present a physical picture of the
phase and discuss its existence in the nearly flatband. Within the picture, we
argue that the FTP at other filling factors can be generated by introducing
proper interactions. The present study contributes to a systematic
understanding of the FTPs and can be realized in cold-atom experiments.Comment: 5 pages, 5 figures. To appear in Phys. Rev.
Complete phase diagram and topological properties of interacting bosons in one-dimensional superlattices
The interacting bosons in one-dimensional inversion-symmetric superlattices
are investigated from the topological aspect. The complete phase diagram is
obtained by an atomic-limit analysis and quantum Monte Carlo simulations and
comprises three kinds of phases: superfluid, persisted charge-density-wave and
Mott insulators, and emergent insulators in the presence of nearest-neighbor
hoppings. We find that all emergent insulators are topological, which are
characterized by the Berry phase and a pair of degenerate in-gap boundary
states. The mechanism of the topological bosonic insulators is qualitatively
discussed and the ones with higher fillings can be understood as a
-filling topological phase on a background of trivial
charge-density-wave or Mott insulators.Comment: 6 pages, 8 figures. Accelpted for publication in Phys. Rev.
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