11,679 research outputs found
Topological characterization of hierarchical fractional quantum Hall effects in topological flat bands with SU() symmetry
We study the many-body ground states of SU() symmetric hardcore bosons on
the topological flat-band model by using controlled numerical calculations. By
introducing strong intracomponent and intercomponent interactions, we
demonstrate that a hierarchy of bosonic SU() fractional quantum Hall (FQH)
states emerges at fractional filling factors (odd ). In
order to characterize this series of FQH states, we figure the effective
matrix from the inverse of the Chern number matrix. The
topological characterization of the matrix also reveals quantized
drag Hall responses and fractional charge pumping that could be detected in
future experiments. In addition, we address the general one-to-one
correspondence to the spinless FQH states in topological flat bands with Chern
number at fillings .Comment: 7 pages, 6 figures. revised versio
Fractional charge pumping of interacting bosons in one-dimensional superlattice
Motivated by experimental realizations of integer quantized charge pumping in
one-dimensional superlattices~[Nat. Phys. 12, 350 (2016); Nat. Phys. 12, 296
(2016)], we generalize and propose the adiabatic pumping of a fractionalized
charge in interacting bosonic systems. This is achieved by dynamically sweeping
the modulated potential in a class of one-dimensional interacting systems. As
concrete examples, we show the charge pumping of interacting bosons at certain
fractionally occupied fillings. We find that, for a given ground state, the
charge pumping in a complete potential cycle is quantized to the fractional
value related to the corresponding Chern number, characterized by the motion of
the charge polarization per site. Moreover, the difference between charge
polarizations of two ground states is quantized to an intrinsic constant
revealing the fractional elementary charge of quasiparticle.Comment: 8 pages,7 figures, revised manuscript; Accepted by Phys. Rev.
Bosonic integer quantum Hall states in topological bands with Chern number two
We study the interacting bosons in topological Hofstadter bands with Chern
number two. Using exact diagonalization, we demonstrate that bosonic integer
quantum Hall (BIQH) state emerges at integer boson filling factor of
the lowest Chern band with evidences including a robust spectrum gap and
quantized topological Hall conductance two. Moreover, the robustness of BIQH
state against different interactions and next-nearest neighbor hopping is
investigated. The strong nearest neighbor interaction would favor a charge
density wave. When the onsite interaction decreases, BIQH state undergoes a
continuous transition into a superfluid state. Without next-nearest neighbor
hopping, the ground state is possibly in a metallic Fermi-liquid-like phase.Comment: 7 pages, 6 figures, References added and minor correctio
Quantum Hall effects of exciton condensate in topological flat bands
Tunable exciton condensates in two dimensional electron gas systems under
strong magnetic field exhibits anomalous Hall transport owing to mutual Coulomb
coupling, and have attracted a lot of research activity. Here, we explore
another framework using topological flat band models in the absence of Landau
levels, for realizing the many-body exciton phases of two-component fermions
under strong intercomponent interactions. By developing new diagnosis based on
the state-of-the-art density-matrix renormalization group and exact
diagonalization, we show the theoretical discovery of the emergence of Halperin
(111) quantum Hall effect at a total filling factor in the lowest Chern
band under strong Hubbard repulsion, which is classified by the unique ground
state with bulk charge insulation and spin superfluidity, The topological
nature is further characterized by one edge branch of chiral propagating
Luttinger modes with level counting in consistent with the
conformal field theory description. Moreover, with nearest-neighbor repulsions,
we propose the Halperin (333) fractional quantum Hall effect at a total filling
factor in the lowest Chern band.Comment: 7 pages, 7 figure
Disorder-driven transition and intermediate phase for fractional quantum Hall effect
The fractional quantum Hall (FQH) effect at the filling number is a
primary candidate for non-Abelian topological order, while the fate of such a
state in the presence of random disorder has not been resolved. Here, we
address this open question by implementing unbiased diagnosis based on
numerical exact diagonalization. We calculate the disorder averaged Hall
conductance and the associated statistical distribution of the topological
invariant Chern number, which unambiguously characterize the disorder-driven
collapse of the FQH state. As the disorder strength increases towards a
critical value, a continuous phase transition is detected based on the disorder
configuration averaged wave function fidelity and the entanglement entropy. In
the strong disorder regime, we identify a composite Fermi liquid (CFL) phase
with fluctuating Chern numbers, in striking contrast to the well-known
case where an Anderson insulator appears. Interestingly, the lowest
Landau level projected local density profile, the wavefunction overlap, and the
entanglement entropy as a function of disorder strength simultaneously signal
an intermediate phase, which may be relevant to the recent proposal of
Pfaffian-anti-Pfaffian puddle state
Possible non-Abelian Moore-Read state in double-layer bosonic fractional quantum Hall system
Identifying and understanding interacting systems that can host non-Abelian
topological phases with fractionalized quasiparticles have attracted intense
attentions in the past twenty years. Theoretically, it is possible to realize a
rich variety of such states by coupling two Abelian fractional quantum Hall
(FQH) states together through gapping out part of the low energy degrees of
freedom. So far, there are some indications, but no robust example has been
established in bilayer systems for realizing the non-Abelian state in the past.
Here, we present a phase diagram of a double-layer bosonic FQH system based on
the exact diagonalization and density-matrix renormalization group (DMRG)
calculations, which demonstrate a potential regime with the emergence of the
non-Abelian bosonic Moore-Read state. We start from the Abelian phase with
fourfold topological degeneracies on torus geometry when the two layers are
weakly coupled. With the increase of interlayer tunneling, we find an
intermediate regime with a threefold groundstate degeneracy and a finite
fractional drag Hall conductance. We find the different topological sectors in
consistent with Moore-Read state by inserting different fluxes in adiabatic
DMRG study. We also extract the modular matrix, which supports
the emergence of the non-Abelian Ising anyon quasiparticle in this system.Comment: 7 figures; 7 page
Chiral and Critical Spin Liquids in Spin- Kagome Antiferromagnet
The topological quantum spin liquids (SL) and the nature of quantum phase
transitions between them have attracted intensive attentions for the past
twenty years. The extended kagome spin-1/2 antiferromagnet emerges as the
primary candidate for hosting both time reversal symmetry (TRS) preserving and
TRS breaking SLs based on density matrix renormalization group simulations. To
uncover the nature of the novel quantum phase transition between the SL states,
we study a minimum XY model with the nearest neighbor (NN) (), the
second and third NN couplings (). We identify the TRS
broken chiral SL (CSL) with the turn on of a small perturbation , which is fully characterized by the fractionally quantized
topological Chern number and the conformal edge spectrum as the
fractional quantum Hall state. On the other hand, the NN XY model ()
is shown to be a critical SL state adjacent to the CSL, characterized by the
gapless spin singlet excitations and also vanishing small spin triplet
excitations. The quantum phase transition from the CSL to the gapless critical
SL is driven by the collapsing of the neutral (spin singlet) excitation gap. By
following the evolution of entanglement spectrum, we find that the transition
takes place through the coupling of the edge states with opposite chiralities,
which merge into the bulk and become gapless neutral excitations. The effect of
the NN spin- coupling is also studied, which leads to a quantum phase
diagram with an extended regime for the gapless SL.Comment: 8 pages, 7 figure
Magnetic field-dependent dynamics and field-driven metal-to-insulator transition of the half-filled Hubbard model: A DMFT+DMRG study
We study the magnetic field driven metal-to-insulator transition in
half-filled Hubbard model on the Bethe lattice, using the dynamical mean-field
theory by solving the quantum impurity problem with density-matrix
renormalization group algorithm. The method enables us to obtain a
high-resolution spectral densities in the presence of a magnetic field. It is
found that the Kondo resonance at the Fermi level splits at relatively high
magnetic field: the spin-up and spin-down components move away from the Fermi
level and finally form a spin polarized band insulator. By calculating the
magnetization and spin susceptibility, we clarify that an applied magnetic
field drives a transition from a paramagnetic metallic phase to a band
insulting phase. In the weak interaction regime, the nature of the transition
is continuous and captured by the Stoner's description, while in the strong
interaction regime the transition is very likely to be metamagnetic, evidenced
by the hysteresis curve. Furthermore, we determine the phase boundary by
tracking the kink in the magnetic susceptibility, and the step-like change of
the entanglement entropy and the entanglement gap closing. Interestingly, the
phase boundary determined from these two different ways are largely consistent
with each other.Comment: 19 pages; 14 figure
Magnetothermoelectric transport properties in phosphorene
We numerically study the electrical and thermoelectric transport properties
in phosphorene in the presence of both a magnetic field and disorder. The
quantized Hall conductivity is similar to that of a conventional
two-dimensional electron gas, but the positions of all the Hall plateaus shift
to the left due to the spectral asymmetry, in agreement with the experimental
observations. The thermoelectric conductivity and Nernst signal exhibit
remarkable anisotropy, and the thermopower is nearly isotropic. When a bias
voltage is applied between top and bottom layers of phosphorene, both
thermopower and Nernst signal are enhanced and their peak values become large.Comment: 8 pages, 9 figure
Interaction-driven fractional quantum Hall state of hard-core bosons on kagome lattice at one-third filling
There has been a growing interest in realizing topologically nontrivial
states of matter in band insulators, where a quantum Hall effect can appear as
an intrinsic property of the band structure. While the on-going progress is
under way with a number of directions, the possibility of realizing novel
interaction-generated topological phases, without the requirement of a
nontrivial invariant encoded in single-particle wavefunction or band structure,
can significantly extend the class of topological materials and is thus of
great importance. Here, we show an interaction-driven topological phase
emerging in an extended Bose-Hubbard model on kagome lattice, where the
non-interacting band structure is topological trivial with zero Berry curvature
in the Brillouin zone. By means of an unbiased state-of-the-art density-matrix
renormalization group technique, we identify that the groundstate in a broad
parameter region is equivalent to a bosonic fractional quantum Hall Laughlin
state, based on the characterization of universal properties including
groundstate degeneracy, edge excitations and anyonic quasiparticle statistics.
Our work paves a way of finding interaction induced topological phase at the
phase boundary of conventionally ordered solid phases.Comment: 8 pages, 8 figure
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