100 research outputs found
Entanglement Spectra of Heisenberg Ladders of higher Spin
We study the entanglement spectrum of Heisenberg spin ladders of arbitrary spin length S in the perturbative regime of strong rung coupling. For isotropic spin coupling the the entanglement spectrum is, within first order perturbation theory, always proportional to the energy spectrum of the single chain with a proportionality factor being also independent of S. A more complicated situation arises for anisotropic ladders of higher spin S>=1 since here even the unperturbed ground state has a nontrivial entanglement spectrum. Finally we discuss related issues in dimerized spin chains
Finite Correlation Length Scaling in Lorentz-Invariant Gapless iPEPS Wave Functions
It is an open question how well tensor network states in the form of an
infinite projected entangled pair states (iPEPS) tensor network can approximate
gapless quantum states of matter. Here we address this issue for two different
physical scenarios: i) a conformally invariant quantum critical point
in the incarnation of the transverse field Ising model on the square lattice
and ii) spontaneously broken continuous symmetries with gapless Goldstone modes
exemplified by the antiferromagnetic Heisenberg and XY models on the
square lattice. We find that the energetically best wave functions display {\em
finite} correlation lengths and we introduce a powerful finite correlation
length scaling framework for the analysis of such finite- iPEPS states. The
framework is important i) to understand the mild limitations of the finite-
iPEPS manifold in representing Lorentz-invariant, gapless many body quantum
states and ii) to put forward a practical scheme in which the finite
correlation length combined with field theory inspired formulae can be
used to extrapolate the data to infinite correlation length, i.e. to the
thermodynamic limit. The finite correlation length scaling framework opens the
way for further exploration of quantum matter with an (expected)
Lorentz-invariant, massless low-energy description, with many applications
ranging from condensed matter to high-energy physics.Comment: 16 pages, 11 figure
The Kagome Heisenberg Antiferromagnet Revisited
We examine the perennial quantum spin-liquid candidate Heisenberg
antiferromagnet on the kagome lattice. Our study is based on achieving Lanczos
diagonalization of the Hamiltonian on a site cluster in sectors with
dimensions as a large as . The results reveal novel intricate
structures in the low-lying energy spectrum. These structures by no means
unambiguously support an emerging consensus of a spin liquid
ground state, but instead appear compatible with several scenarios, including
four-fold topological degeneracy, inversion symmetry breaking and a combination
thereof. We discuss finite-size effects, such as the apparent absence of ETH,
and note that while considerably reduced, some are still present for the
largest cluster. Finally, we observe that an XXZ model in the Ising limit
reproduces remarkably well the most striking features of finite-size spectra.Comment: 8 pages, 5 figure
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