45,533 research outputs found
Hidden spin current in doped Mott antiferromagnets
We investigate the nature of doped Mott insulators using exact
diagonalization and density matrix renormalization group methods. Persistent
spin currents are revealed in the ground state, which are concomitant with a
nonzero total momentum or angular momentum associated with the doped hole. The
latter determines a nontrivial ground state degeneracy. By further making
superpositions of the degenerate ground states with zero or unidirectional spin
currents, we show that different patterns of spatial charge and spin
modulations will emerge. Such anomaly persists for the odd numbers of holes,
but the spin current, ground state degeneracy, and charge/spin modulations
completely disappear for even numbers of holes, with the two-hole ground state
exhibiting a d-wave symmetry. An understanding of the spin current due to a
many-body Berry-like phase and its impact on the momentum distribution of the
doped holes will be discussed.Comment: 9 pages, 9 figures, update second version including more data and
discussion adde
Pairing versus phase coherence of doped holes in distinct quantum spin backgrounds
We examine the pairing structure of holes injected into two \emph{distinct}
spin backgrounds: a short-range antiferromagnetic phase versus a symmetry
protected topological phase. Based on density matrix renormalization group
(DMRG) simulation, we find that although there is a strong binding between two
holes in both phases, \emph{phase fluctuations} can significantly influence the
pair-pair correlation depending on the spin-spin correlation in the background.
Here the phase fluctuation is identified as an intrinsic string operator
nonlocally controlled by the spins. We show that while the pairing amplitude is
generally large, the coherent Cooper pairing can be substantially weakened by
the phase fluctuation in the symmetry-protected topological phase, in contrast
to the short-range antiferromagnetic phase. It provides an example of a non-BCS
mechanism for pairing, in which the paring phase coherence is determined by the
underlying spin state self-consistently, bearing an interesting resemblance to
the pseudogap physics in the cuprate.Comment: 9 pages, 6 figure
Intrinsic translational symmetry breaking in a doped Mott insulator
A central issue of Mott physics, with symmetries being fully retained in the
spin background, concerns the charge excitation. In a two-leg spin ladder with
spin gap, an injected hole can exhibit either a Bloch wave or a density wave by
tuning the ladder anisotropy through a `quantum critical point' (QCP). The
nature of such a QCP has been a subject of recent studies by density matrix
renormalization group (DMRG). In this paper, we reexamine the ground state of
the one doped hole, and show that a two-component structure is present in the
density wave regime in contrast to the single component in the Bloch wave
regime. In the former, the density wave itself is still contributed by a
standing-wave-like component characterized by a quasiparticle spectral weight
in a finite-size system. But there is an additional charge incoherent
component emerging, which intrinsically breaks the translational symmetry
associated with the density wave. The partial momentum is carried away by
neutral spin excitations. Such an incoherent part does not manifest in the
single-particle spectral function, directly probed by the angle-resolved
photoemission spectroscopy (ARPES) measurement, however it is demonstrated in
the momentum distribution function. The Landau's one-to-one correspondence
hypothesis for a Fermi liquid breaks down here. The microscopic origin of this
density wave state as an intrinsic manifestation of the doped Mott physics will
be also discussed.Comment: 11 pages, 6 figures, an extended version of arXiv:1601.0065
Numerical Study of Quantum Hall Bilayers at Total Filling : A New Phase at Intermediate Layer Distances
We study the phase diagram of quantum Hall bilayer systems with total filing
of the lowest Landau level as a function of layer distances
. Based on numerical exact diagonalization calculations, we obtain three
distinct phases, including an exciton superfluid phase with spontaneous
interlayer coherence at small , a composite Fermi liquid at large , and
an intermediate phase for ( is the magnetic length). The
transition from the exciton superfluid to the intermediate phase is identified
by (i) a dramatic change in the Berry curvature of the ground state under
twisted boundary conditions on the two layers; (ii) an energy level crossing of
the first excited state. The transition from the intermediate phase to the
composite Fermi liquid is identified by the vanishing of the exciton superfluid
stiffness. Furthermore, from our finite-size study, the energy cost of
transferring one electron between the layers shows an even-odd effect and
possibly extrapolates to a finite value in the thermodynamic limit, indicating
the enhanced intralayer correlation. Our identification of an intermediate
phase and its distinctive features shed new light on the theoretical
understanding of the quantum Hall bilayer system at total filling .Comment: 5 pages, 3 figures (main text); 5 pages, 4 figures (supplementary
material); to be published in PR
Robust non-Abelian spin liquid and possible intermediate phase in antiferromagnetic Kitaev model with magnetic field
We investigate the non-Abelian topological chiral spin liquid phase in the
two-dimensional (2D) Kitaev honeycomb model subject to a magnetic field. By
combining density matrix renormalization group (DMRG) and exact diagonalization
(ED) we study the energy spectra, entanglement, topological degeneracy, and
expectation values of Wilson loop operators, allowing for robust
characterization. While the ferromagnetic (FM) Kitaev spin liquid is already
destroyed by a weak magnetic field with Zeeman energy , the antiferromagnetic (AFM) spin liquid remains robust up to a magnetic
field that is an order of magnitude larger, .
Interestingly, for larger fields , an
intermediate gapless phase is observed, before a second transition to the
high-field partially-polarized paramagnet. We attribute this rich phase
diagram, and the remarkable stability of the chiral topological phase in the
AFM Kitaev model, to the interplay of strong spin-orbit coupling and
frustration enhanced by the magnetic field. Our findings suggest relevance to
recent experiments on RuCl under magnetic fields.Comment: 8 pages, 8 figure
Charge dynamics in the phase string model for high-Tc superconductors
An understanding of the anomalous charge dynamics in the high-Tc cuprates is
obtained based on a model study of doped Mott insulators. The high-temperature
optical conductivity is found to generally have a two-component structure: a
Drude like part followed by a mid-infrared band. The scattering rate associated
with the Drude part exhibits a linear-temperature dependence over a wide range
of high temperature, while the Drude term gets progressively suppressed below a
characteristic energy of magnetic origin as the system enters the pseudogap
phase. The high-energy optical conductivity shows a resonancelike feature in an
underdoped case and continuously evolves into a 1/\omega tail at higher doping,
indicating that they share the same physical origin. In particular, such a
high-energy component is closely correlated with the \omega-peak structure of
the density-density correlation function at different momenta, in systematic
consistency with exact diagonalization results based on the t-J model. The
underlying physics is attributed to the high-energy spin-charge separation in
the model, in which the "mode coupling" responsible for the anomalous charge
properties is not between the electrons and some collective mode but rather
between new charge carriers, holons, and a novel topological gauge field
controlled by spin dynamics, as the consequence of the strong short-range
electron-electron Coulomb repulsion in the doped Mott insulator.Comment: 19 pages, 13 figures; final version to appear in Phys. Rev.
- β¦